Dist/carb tuning question
Printed From: CorrectCraftFan.com
Category: Repairs and Maintenance
Forum Name: Boat Maintenance
Forum Discription: Discuss maintenance of your Correct Craft
URL: http://www.CorrectCraftFan.com/forum/forum_posts.asp?TID=11218
Printed Date: June-22-2024 at 11:10pm
Topic: Dist/carb tuning question
Posted By: BuffaloBFN
Subject: Dist/carb tuning question
Date Posted: July-14-2008 at 7:22pm
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I'm slowly getting my engine dialed in and I'd like to bounce this off of the pros. My DUI dist instructions say to set my initial timing at 12 BTDC and go as far as 14 depending on emission requirements and whether or not a ping is heard. I think the emissions thing is only for CA and I haven't heard a ping at either setting. The difference is that at 12 degrees it stumbles around 3700 rpm's and at 14 it runs on up to 4000. I realize my prop may be a bit oversized and that I probably need to raise the secondary floats a little more...but why the difference based on timing?
I put the timing back to 12 because it popped through the carb once at 4000 with the timing at 14. The jets are 76 and the PV is 7.5 13-14" of vacuum at 700 rpm's Thanks guys.  ------------- http://correctcraftfan.com/diaries/details.asp?ID=2331&sort=&pagenum=12&yrstart=1986&yrend=1990" rel="nofollow - 1988 BFN-sold "It's a Livin' Thing...What a Terrible Thing to Lose" ELO |
Replies:
Posted By: BuffaloBFN
Date Posted: July-15-2008 at 10:02am
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I meant to include this too; the secondaries start to open around 2100-2200 under hard acceleration and about 2800 on average acceleration. ------------- http://correctcraftfan.com/diaries/details.asp?ID=2331&sort=&pagenum=12&yrstart=1986&yrend=1990" rel="nofollow - 1988 BFN-sold "It's a Livin' Thing...What a Terrible Thing to Lose" ELO |
Posted By: TRBenj
Date Posted: July-15-2008 at 3:41pm
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Greg, thats strange. Are you sure youre timing the boat properly? I know next to nothing about the BBC's, but from what I know about the SBF's here are my comments:
- Stock (initial) timing in the 6-14 deg range should give you reliable performance, though the higher the better (without pinging). I only got some popping and hesitation when my 302 was set to 0 deg. - Are you only getting 4k RPM at WOT? That seems awfully low. What prop are you running? What did you spin for RPM before the rebuild? - Ive never seen vaccuum secondaries open that early. All of my boats open around 3500-4000 RPM, regardless of load. ------------- |
Posted By: BuffaloBFN
Date Posted: July-15-2008 at 5:10pm
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Thanks for the response Tim. When you say 'higher', do you mean a larger # before TDC or the opposite? Does advancing the timing mean farther or closer to TDC? I thought I understood this, but I feel turned around?!!?
I'm baffled at the moment but do expect to get a book tomorrow. The throttle has the travel to go where it should, but it stumbles. How much does timing affect when the secondaries open if at all? ------------- http://correctcraftfan.com/diaries/details.asp?ID=2331&sort=&pagenum=12&yrstart=1986&yrend=1990" rel="nofollow - 1988 BFN-sold "It's a Livin' Thing...What a Terrible Thing to Lose" ELO |
Posted By: TRBenj
Date Posted: July-15-2008 at 6:06pm
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All timing is BTDC. Initial will be in the 6-14 deg BTDC, final will advance somewhere on the order of 24 deg to a final of 30+ deg BTDC.
Timing wont have an affect on when the secondaries come in- thats based on vaccuum. For whatever reason, I never see the secondaries come in until 3500+ RPM, regardless of load. ------------- |
Posted By: backfoot100
Date Posted: July-15-2008 at 6:29pm
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I gotta agree with Tim. The secondaries should open a lot higher than that. It's based soley on the vacuum from the engine. Almost sounds like the carb is way undersized if they're opening that soon. Another thing you can do is get different size springs to put in the vacuum diaphram to adjust when the secondaries come in at. I've just never heard of the secondaries coming in that soon. ------------- When people run down to the lake to see what's making that noise, you've succeeded. Eddie |
Posted By: BuffaloBFN
Date Posted: July-15-2008 at 8:49pm
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Thanks Eddie and Tim. To clarify, that's when I saw them start to open.
I don't think the carb is undersized...it's a 750 DP. I think I'm going to hook the old 600 edelbrock up just to see how it acts. I haven't been back through my bowtie thread, but I'm pretty sure I remember Chris(79) saying I was going to have probs with my holley 750 because the floats are center hung rather than side hung. As it is, the 750 runs beautifully until it gets around 3600 rpm's, but I do think it's burning too much gas. Maybe the early secondaries are flooding it?...but it acts like it's starving for fuel on top. I used to have a TV that required a smack on the side...guess that won't work on this?!!? LOL ------------- http://correctcraftfan.com/diaries/details.asp?ID=2331&sort=&pagenum=12&yrstart=1986&yrend=1990" rel="nofollow - 1988 BFN-sold "It's a Livin' Thing...What a Terrible Thing to Lose" ELO |
Posted By: BuffaloBFN
Date Posted: July-17-2008 at 9:48am
It's definately running rich. I pulled the plugs yesterday and both electrodes are clean and all of the plugs are burning evenly, but the surrounding area is sooty. I haven't tried the 600 yet...kinda hard to kick a new carb to the curb. 
I have another small issue as well...I'll have to spend a few minutes cleaning up the jawbones that are scattered all over the boat?!!? LOL I pulled a few of my new neighbors last night. They're mostly new to wakeboarding and are used to a 6 cylinder I/O. A few had never been behind an inboard and none had ever been behind a BFN...maybe it was the noise they weren't used to?!!?  ------------- http://correctcraftfan.com/diaries/details.asp?ID=2331&sort=&pagenum=12&yrstart=1986&yrend=1990" rel="nofollow - 1988 BFN-sold "It's a Livin' Thing...What a Terrible Thing to Lose" ELO |
Posted By: eric lavine
Date Posted: July-17-2008 at 10:11am
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Greg, how many hours and what type of rings did you use? it takes a while for mollys to break in and as they break in will create more vacuum at the lower end, i dont think the 750 is to big, if the rings have'nt quite seated completely you will experience some of the problems your having such as running rich and possibly throwing off when the secondaries are opening,
are you getting any blow by out of the valve covers? if so that is a sure sign that the rings are not quite broke in completely, your better off running rich right now than lean untill you get the problem figured out, the vacuum readings you are seeing is what is throwing me off, i think you should be seeing at touch more vacuum at idle unless your running a high cam, but i believe you said you were going to run the stock broomstick |
Posted By: BuffaloBFN
Date Posted: July-17-2008 at 11:02am
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I have about 7 hours on it now. They are moly rings from hastings, and I'll check for blow by. I do have the stock broomstick...that was a $2500 decision. The only mods were the performer intake, carb, dist., and it's .030 over. DUI calibrated the dist to have 24 degrees @ 3000, so I'll check that today.
Does the taller intake affect vacuum? ------------- http://correctcraftfan.com/diaries/details.asp?ID=2331&sort=&pagenum=12&yrstart=1986&yrend=1990" rel="nofollow - 1988 BFN-sold "It's a Livin' Thing...What a Terrible Thing to Lose" ELO |
Posted By: TRBenj
Date Posted: July-17-2008 at 11:29am
Double pumper = mechanical secondaries? Or do you have vaccuum secondaries? ------------- |
BuffaloBFN wrote:Posted By: BuffaloBFN
Date Posted: July-17-2008 at 11:51am
Vacuum ------------- http://correctcraftfan.com/diaries/details.asp?ID=2331&sort=&pagenum=12&yrstart=1986&yrend=1990" rel="nofollow - 1988 BFN-sold "It's a Livin' Thing...What a Terrible Thing to Lose" ELO |
Posted By: lewy2001
Date Posted: July-17-2008 at 12:21pm
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What is your advance curve like. It sounds like it is not getting enough advance as you go higher in the rev range this will create a rich condition as you wont be getting spark when it is required resulting in unburnt fuel.
First check that the TDC mark on the balancer is actually tdc. If you have a graduated balancer you can check the advance curve at different rev ranges. If not just add a couple of more notches on your balancer at say 25, 30 and 35. Not sure of the total advance a BBC can handle but the SBC was around 38-40 degrees before detonation. I used to set my warm 350 chev at 36 degrees at 4200rpm. Possibly a simple way of proving this is adding more static advance in 2 degree increments and then running the boat at the higher rpms. I used to run 18 degress static advance on my SBC. A 750cfm vac secondaries carby should be fine a 454 cu in motor 600cfm would be a bit small at higher rpms but would give good throttle response out of the hole and good economy. Hope this helps might be worth a try before swapping carby's. ------------- If you're going through hell, keep going http://www.correctcraftfan.com/diaries/details.asp?ID=2999" rel="nofollow - 89 Ski <a href="http://www.correctcraftfan.com/diaries/details.asp?ID=5685" ta |
Posted By: 79nautique
Date Posted: July-17-2008 at 12:39pm
well the curve was set by the wonderfull masters of distributors at DUI that believe 24 max advance is great for these beast of a motor we use PR BS way too many have bought into and left perfomance on the table because of. And the rich fuel washed down cyclinders are real good for blow by but horrible for seating rings ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=756&sort=&pagenum=1&yrstart=1979&yrend=1979 - 79 nautique |
Posted By: BuffaloBFN
Date Posted: July-17-2008 at 1:05pm
Thanks Lewy. I talked to a friend last night who agrees with you on the advance. He also thinks the PV may be too large. I still have the mallory dist that was in it, maybe I'll switch that back? ------------- http://correctcraftfan.com/diaries/details.asp?ID=2331&sort=&pagenum=12&yrstart=1986&yrend=1990" rel="nofollow - 1988 BFN-sold "It's a Livin' Thing...What a Terrible Thing to Lose" ELO |
Posted By: eric lavine
Date Posted: July-17-2008 at 1:45pm
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way to much fuel will wash the cylinders but if you pull the dipstick and smell unburnt fuel or raw fuel you got problems, i have scattered a motor because of too much carb, it washed the cylinders and didnt take long. its a fine line and the statement was in regards to no back fires because of too much fuel...it just sounds like its running a touch rich and will straighten out with time and then dial her in. the engine is in the recovery room after the operation and it takes some time to seat the molly's
the vacuum guage is the true source of what is going on and it seemed low due to the rings not seating yet, with a stock cam i would think you should be pulling 16 to 18 inches as a good running engine should |
Posted By: BuffaloBFN
Date Posted: July-17-2008 at 1:59pm
And the surgeon was a butcher?!!? LOL I found my bonehead mistake. I've been running it 'cold' because I forgot to run the dedicated 12 gauge wire to the dist. There may still be more to it, but I'll fix that first. ------------- http://correctcraftfan.com/diaries/details.asp?ID=2331&sort=&pagenum=12&yrstart=1986&yrend=1990" rel="nofollow - 1988 BFN-sold "It's a Livin' Thing...What a Terrible Thing to Lose" ELO |
Posted By: eric lavine
Date Posted: July-17-2008 at 2:10pm
| Jitters again my friend? |
Posted By: 79nautique
Date Posted: July-17-2008 at 2:31pm
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running larger wire to the dist won't change anything. might give little more spark energy but nothing to the advance ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=756&sort=&pagenum=1&yrstart=1979&yrend=1979 - 79 nautique |
Posted By: BuffaloBFN
Date Posted: July-17-2008 at 2:32pm
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I'm sure I could come up with a list of excuses, and I read the instruction sheet several times; but the fact is I forgot to do it.
------------- http://correctcraftfan.com/diaries/details.asp?ID=2331&sort=&pagenum=12&yrstart=1986&yrend=1990" rel="nofollow - 1988 BFN-sold "It's a Livin' Thing...What a Terrible Thing to Lose" ELO |
Posted By: 79nautique
Date Posted: July-17-2008 at 2:36pm
if it didn't have 12v all ready at the dist then it wouldn't run at all your starting to chase your tail and it's not looking pretty. ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=756&sort=&pagenum=1&yrstart=1979&yrend=1979 - 79 nautique |
Posted By: BuffaloBFN
Date Posted: July-18-2008 at 1:20pm
I did have 12 volts before, but DUI wants 14.5 and I now have 14.47 with the dedicated wire. I pulled 1 skier after the switch last night and it did burn a little cleaner and smoother, but it's still rich. I also verified that TDC is TDC and checked the advance. The initial timing is much more stable than it was and the advance seems to be right on. I still haven't swithed the carb or dist. I'm trying to do 1 thing at a time so I don't get dizzy from chasing my tail! Next I was thinking of dropping the jet and PV sizes. The jets are 76's now, and the PV is a 7.5 Thoughts? ------------- http://correctcraftfan.com/diaries/details.asp?ID=2331&sort=&pagenum=12&yrstart=1986&yrend=1990" rel="nofollow - 1988 BFN-sold "It's a Livin' Thing...What a Terrible Thing to Lose" ELO |
Posted By: 79nautique
Date Posted: July-18-2008 at 1:31pm
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how are you stepping up the voltage your not going to get 14.5 volts out of a 12 volt battery and your just going to burn up the electronics if you do anyway, another great bit of advice along with the 24 degrees of total advance. The more you guys talk about those DUI units and what they are telling you to do just shows me they are full of it.
pv 6.5-5.5 but you need to get that rich carb fixed before you burn off all of the honing marks in the cylinders leaving power on the table big time. ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=756&sort=&pagenum=1&yrstart=1979&yrend=1979 - 79 nautique |
Posted By: BuffaloBFN
Date Posted: July-18-2008 at 1:36pm
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As I understand it, it's full alternator voltage. It's a 12 gauge wire from the ignition post to the dist.
As far as fixing the rich carb, I thought smaller jets and PV would work towards that end. ------------- http://correctcraftfan.com/diaries/details.asp?ID=2331&sort=&pagenum=12&yrstart=1986&yrend=1990" rel="nofollow - 1988 BFN-sold "It's a Livin' Thing...What a Terrible Thing to Lose" ELO |
Posted By: 79nautique
Date Posted: July-18-2008 at 1:40pm
this is your biggest issue not enough timing you should have at least 30 degrees at this rpm 24 is what you should have just after 2K oh well the DUI guys know how to get people to buy into BS if nothing else. Easy to sell parts to the unknowing uninformed folks out there especially with all of the free PR they get here. ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=756&sort=&pagenum=1&yrstart=1979&yrend=1979 - 79 nautique |
Posted By: 79nautique
Date Posted: July-18-2008 at 1:43pm
from what ign post alternator? ign switch? did you keep the ballast resistor in the loop or something on the orginal wire? Sounds a little squirlly to me. ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=756&sort=&pagenum=1&yrstart=1979&yrend=1979 - 79 nautique |
Posted By: BuffaloBFN
Date Posted: July-18-2008 at 2:58pm
It runs from the ignition swith straight to the dist. The ballast resistor is bypassed. ------------- http://correctcraftfan.com/diaries/details.asp?ID=2331&sort=&pagenum=12&yrstart=1986&yrend=1990" rel="nofollow - 1988 BFN-sold "It's a Livin' Thing...What a Terrible Thing to Lose" ELO |
Posted By: 79nautique
Date Posted: July-18-2008 at 3:13pm
would have been much easier to tap in the battery lead at the back of the motor, still don't understand the need, existing wire should have been fine, oh enjoy the hassles of not having it curved right. ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=756&sort=&pagenum=1&yrstart=1979&yrend=1979 - 79 nautique |
Posted By: TRBenj
Date Posted: July-18-2008 at 4:26pm
Chris, he means 24 degrees of advance is built into the dizzy. You have to add the base timing to that 24 degrees to get the total advance. No idea if thats a good set up for a BBC, but 24 degrees of advance works great on my SBF. Greg, your old carb was an edelbrock, correct? It would be interesting to know what the stock jet sizes would have been with a Holley. Its just a WAG, but Id say 76 on the primaries would be quite rich. Maybe try dropping it a few (maybe a 74 or 72), run it briefly to see if performance improves and do a plug chop. ------------- |
Posted By: BuffaloBFN
Date Posted: July-18-2008 at 4:34pm
Thanks Tim, I just picked up some 71's and a 2.5 and 4.5 PV along with the necessary gaskets. I'll get it surrounded soon! Chris, FWIW you didn't have a problem with the DUI when I bought it. ------------- http://correctcraftfan.com/diaries/details.asp?ID=2331&sort=&pagenum=12&yrstart=1986&yrend=1990" rel="nofollow - 1988 BFN-sold "It's a Livin' Thing...What a Terrible Thing to Lose" ELO |
Posted By: 79nautique
Date Posted: July-18-2008 at 4:45pm
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will Tim what he types and what you say are two different things and set for 24 @ 3000 is 24 total advance and you don't add in the base timing to the figure.
It's real easy to figure out the actual advance with a quality timing light and you can actual set the rpm with the right light as well so if you have not reach full advance by 3k then you have it all curved wrong but then again your just guessing because you or he didn't do the work and haven't verifiy the actual timing at all, you are going by what you where told so speak in terms that are relevent not that I get 24 more degrees of advance over base timing at 3k horse ***************, max, total, final advance for a stock cam at 36-38 degress BTDC will ping ping ping like no tomorrow. Again get your head out of the book and spec sheet and live in the real world with real perfomance all around not just out of the hole. ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=756&sort=&pagenum=1&yrstart=1979&yrend=1979 - 79 nautique |
Posted By: 79nautique
Date Posted: July-18-2008 at 4:56pm
Don't have a problem with it it's just that you guys are leaving so much on the table by not doing it your self. Look at this way it sure sounds like Tim's and yours are curved exactly the same way, 24 degrees of advance is built in on both regardless of base setting but the odd thing is you have two completely different cam profiles and two completely different motors and since they are not apples to apples then how in the hell can the advance profiles be the same? How because you bought in to a bunch of BS, said that it's fine would look orginal never said that it would be set up correctly and running the wire the way you did was a big waist and thinking your going to get 14.5v to the coil all of the time is a big joke as well. Just keep a spare module on board and replace the cap often. ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=756&sort=&pagenum=1&yrstart=1979&yrend=1979 - 79 nautique |
Posted By: TRBenj
Date Posted: July-18-2008 at 4:58pm
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Greg, just ignore Chris- he'll disagree with me no matter what I say, and since I like my DUI he has to say that its junk.
Set your base timing to 12 degrees, try the smaller jets, and report back. ------------- |
Posted By: BuffaloBFN
Date Posted: July-18-2008 at 5:05pm
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I was going to ask him who pissed in his corn flakes?!!? ------------- http://correctcraftfan.com/diaries/details.asp?ID=2331&sort=&pagenum=12&yrstart=1986&yrend=1990" rel="nofollow - 1988 BFN-sold "It's a Livin' Thing...What a Terrible Thing to Lose" ELO |
Posted By: 79nautique
Date Posted: July-18-2008 at 5:11pm
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sorry if you don't know the difference between total/final advance and built-in distributor advance two completely different things and when talking about dist advance you should be refering to actual advance on the motor and checking it while the motor is running not from some spec sheet joe blow provided.
Again it all goes back to the skill of the hand turning the wrenches you can either do it your self or get someone else 2000 miles away that will get you close, sorry you choose the later sorry you don't have the skill to do it your self, do you really think Doc would have went with the Unilite if he thought the DUI was better? Do you really? I don't. Do you really think you have more experince and first hand knowledge about the HEI distributor's design, functionalty and inner workings or ignitions systems in general than someone that actually worked on them for a living while they where still in production? some one that had to fix all of the little warrenty issue's that had to be fixed to improve the product? doubt it but then again I'm not a EE I don't focus on a small aspect of the big picture I have to look at the whole picture because it's the sum of the parts not some small electrical curcuit that doesn't move. ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=756&sort=&pagenum=1&yrstart=1979&yrend=1979 - 79 nautique |
Posted By: BuffaloBFN
Date Posted: July-18-2008 at 5:19pm
I did verify TDC and have marked my balancer for 28 and 35 degrees. A well qualified friend told me how!  ------------- http://correctcraftfan.com/diaries/details.asp?ID=2331&sort=&pagenum=12&yrstart=1986&yrend=1990" rel="nofollow - 1988 BFN-sold "It's a Livin' Thing...What a Terrible Thing to Lose" ELO |
Posted By: 79nautique
Date Posted: July-18-2008 at 5:32pm
the well qualify friend should have had a quality timing light as that is the most accurate method to determind total advance at a given RPM and that is what is important. And the big mark and big notch are the best marks to keep lined up but then you have to have the tools for the job to do it right at least. ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=756&sort=&pagenum=1&yrstart=1979&yrend=1979 - 79 nautique |
Posted By: BuffaloBFN
Date Posted: July-18-2008 at 6:07pm
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Timing light in use sir! ------------- http://correctcraftfan.com/diaries/details.asp?ID=2331&sort=&pagenum=12&yrstart=1986&yrend=1990" rel="nofollow - 1988 BFN-sold "It's a Livin' Thing...What a Terrible Thing to Lose" ELO |
Posted By: BuffaloBFN
Date Posted: July-18-2008 at 6:57pm
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There were 2 gaskets on the PV...both of the new ones I bought came with 1. Maybe this was a problem? ------------- http://correctcraftfan.com/diaries/details.asp?ID=2331&sort=&pagenum=12&yrstart=1986&yrend=1990" rel="nofollow - 1988 BFN-sold "It's a Livin' Thing...What a Terrible Thing to Lose" ELO |
Posted By: BuffaloBFN
Date Posted: July-18-2008 at 8:46pm
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I put in the 71's and a 4.5 PV. It's better but still not right. It stumbles now at 3900-4000 instead of 3700. Maybe I should have put the 2.5 in it?
Should the breather hose be pluged when checking the vacuum...or is there not supposed to be any vacuum there at all? ------------- http://correctcraftfan.com/diaries/details.asp?ID=2331&sort=&pagenum=12&yrstart=1986&yrend=1990" rel="nofollow - 1988 BFN-sold "It's a Livin' Thing...What a Terrible Thing to Lose" ELO |
Posted By: BuffaloBFN
Date Posted: July-19-2008 at 1:33am
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The verdict is in...a 750 is entirely too large for my application. I put the edelbrock/weber 600 back on it and I have full throttle response, smooth idle at 600(550 in gear), and a smile to prove it!
3 cheers from Amy and I to the Boat Dr.!!! 
He has patiently walked me through the workings of a carb, and I now have a much better understanding of V/E. Doc, I told you wrong about the prop. I pulled the receipt, and it's a 14x14 with a 200 rpm cup that needs to be removed. That and the flame arrestor sticking up higher again are the only things to work out for the moment. Thanks for everyone's input; oil change first thing in the morning, and I'll make sure to finish seating the rings tomorrow! ------------- http://correctcraftfan.com/diaries/details.asp?ID=2331&sort=&pagenum=12&yrstart=1986&yrend=1990" rel="nofollow - 1988 BFN-sold "It's a Livin' Thing...What a Terrible Thing to Lose" ELO |
Posted By: SNobsessed
Date Posted: July-19-2008 at 1:59am
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Greg - I bet you sleep good tonight having this figured out! ------------- “Beer is proof that God loves us and wants us to be happy.” Ben Franklin |
Posted By: BuffaloBFN
Date Posted: July-19-2008 at 2:03am
Ya Mon!  ------------- http://correctcraftfan.com/diaries/details.asp?ID=2331&sort=&pagenum=12&yrstart=1986&yrend=1990" rel="nofollow - 1988 BFN-sold "It's a Livin' Thing...What a Terrible Thing to Lose" ELO |
Posted By: 8122pbrainard
Date Posted: July-19-2008 at 10:43am
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Greg,
Don't jump in on having that cup removed from the prop . It was discovered in the early 60's that the cupping drastically reduced cavitation and is the reason for it. I'd continue tweaking the engine and then if needed have the prop re pitched or try another prop. ------------- /diaries/details.asp?ID=1622" rel="nofollow - 54 Atom /diaries/details.asp?ID=2179" rel="nofollow - 77 Tique 64 X55 Dunphy Keep it original, Pete < |
Posted By: eric lavine
Date Posted: July-19-2008 at 11:31am
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id be curious to see what your vacuum readings will be now, the smaller throat should increase the readings to where they should be, are you stuck with the carb? can you return? i think the doc hit the nail on the head, stock cam, no increase on intake air and the 600 would seem a touch small but it isnt.
I would think if you went with a hotter cam to where the valves opened taller and stayed open longer the 750 wouldve suited the engine fine.....its a fine line, glad you got her straightened out |
Posted By: BuffaloBFN
Date Posted: July-19-2008 at 3:11pm
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I don't think I'll be stuck with it, but I can't get the guy on the phone. He may be out of town. If I do wind up stuck with it, I'll try to trade for a 650 and there may be another place or 2 around here that might want it. The carb I'm using now is mechanical advance and won't accept the factory flame arrestor...so I think I'll put it back the way the Meloons had it.
I think there's a lesson in that last statement somewhere...but with my thick head?!!? LOL ------------- http://correctcraftfan.com/diaries/details.asp?ID=2331&sort=&pagenum=12&yrstart=1986&yrend=1990" rel="nofollow - 1988 BFN-sold "It's a Livin' Thing...What a Terrible Thing to Lose" ELO |
Posted By: eric lavine
Date Posted: July-20-2008 at 10:38am
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restriction creates vacuum, the writing was on the wall and the restriction is the throat of the carb, good call
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Posted By: GottaSki
Date Posted: July-21-2008 at 1:52pm
I think Chris is still onto something here, when mapping timing on a 425HP model, I was amazed at the final timing the engine liked. I would do a disservice spouting numbers, but it was markedly more than the SBF numbers I was used to (35-36 for a 351). These two distributers having the exact same span is suspicious to me too. It may run fine now, but I suspect there is untapped potential in the engine with enough research, patience and skeptacism in the dist/carb hardware to find it and sort it out. I suggest find the initial the boat likes for a hard launch (usually the most it can take without a labored hot start) find the final the boat likes (have someone drive while twising the dist till no positive affect, then pull a lttle back for a comfort margin, measure this timing. Compare to baseline for similare engines. Subtract the two, and set the span on the advance to this number. this optimizes the min and max. Then play with the curve after you correct some carburation. ------------- "There is nothing, absolutely nothing, half so much worthwhile as messing around with boats...simply messing." River Rat to Mole |
Posted By: 79nautique
Date Posted: July-21-2008 at 2:02pm
why do all that like a real mechanic would when you all ready have the so called experts doing it for you at performance distributors where it was bought from. why because they are un-educated in the skill of adjusting a dist. correctly. ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=756&sort=&pagenum=1&yrstart=1979&yrend=1979 - 79 nautique |
Posted By: BuffaloBFN
Date Posted: July-21-2008 at 2:09pm
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For now it likes 14 degrees.
Just found out I can't return it, so I'll be looking to sell or trade it for a 650. Thanks for the additional input and I'll do what has been suggested when I round up the carb. ------------- http://correctcraftfan.com/diaries/details.asp?ID=2331&sort=&pagenum=12&yrstart=1986&yrend=1990" rel="nofollow - 1988 BFN-sold "It's a Livin' Thing...What a Terrible Thing to Lose" ELO |
Posted By: eric lavine
Date Posted: July-21-2008 at 2:11pm
| how much vacuum? get a reading at the same port and RPM, im curious, you were at 13 to 14 at 700 rpm before |
Posted By: BuffaloBFN
Date Posted: July-22-2008 at 9:17am
|
Eric, I'll try to get those #'s today, but I was using the port on the carb that is no longer there.
Think I found(with help) what I need... http://www.jegs.com/i/Holley/510/0-80552++++++++++++++/10002/-1/743728%7C10271 - carb ------------- http://correctcraftfan.com/diaries/details.asp?ID=2331&sort=&pagenum=12&yrstart=1986&yrend=1990" rel="nofollow - 1988 BFN-sold "It's a Livin' Thing...What a Terrible Thing to Lose" ELO |
Posted By: 79nautique
Date Posted: July-22-2008 at 11:39am
sorry try again the inlet is not the style you need. ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=756&sort=&pagenum=1&yrstart=1979&yrend=1979 - 79 nautique |
Posted By: BuffaloBFN
Date Posted: July-22-2008 at 11:41am
The fuel inlet? ------------- http://correctcraftfan.com/diaries/details.asp?ID=2331&sort=&pagenum=12&yrstart=1986&yrend=1990" rel="nofollow - 1988 BFN-sold "It's a Livin' Thing...What a Terrible Thing to Lose" ELO |
Posted By: 79nautique
Date Posted: July-22-2008 at 11:42am
no the AIR inlet ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=756&sort=&pagenum=1&yrstart=1979&yrend=1979 - 79 nautique |
Posted By: BuffaloBFN
Date Posted: July-22-2008 at 11:49am
You mean because it's a quadrajet replacement? I have a quadrajet manifold...the original is as well. ------------- http://correctcraftfan.com/diaries/details.asp?ID=2331&sort=&pagenum=12&yrstart=1986&yrend=1990" rel="nofollow - 1988 BFN-sold "It's a Livin' Thing...What a Terrible Thing to Lose" ELO |
Posted By: BuffaloBFN
Date Posted: July-22-2008 at 11:54am
|
Chris, if you know something, I wish you'd explain. The carb will ship today... ------------- http://correctcraftfan.com/diaries/details.asp?ID=2331&sort=&pagenum=12&yrstart=1986&yrend=1990" rel="nofollow - 1988 BFN-sold "It's a Livin' Thing...What a Terrible Thing to Lose" ELO |
Posted By: 79nautique
Date Posted: July-22-2008 at 11:56am
|
yes the inlet for the fuel why you are worried about getting a 650 to replace the 600 which will still flow 650 if you read the fine print on holley's site beats the hell out of me
But your inlet should be more like this style http://store.summitracing.com/partdetail.asp?part=HLY%2D0%2D80319%2D1&view=1&N=700+150+400178+4294908331+ - carb ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=756&sort=&pagenum=1&yrstart=1979&yrend=1979 - 79 nautique |
Posted By: BuffaloBFN
Date Posted: July-22-2008 at 12:12pm
|
Thanks Chris, I appreciate your patience. I called and asked the tech guy and the pic may not be an exact match. He said it would be like the one you posted. If it's not right, maybe I'll have to switch the bowl.
As you say, it runs darn well with the 600...until I get a boat full of people. This is only my feeling, but comparing to the 750 it now wants a little more. The other thing is my cover won't close with the edelbrock and I don't want to raise it up any more. ------------- http://correctcraftfan.com/diaries/details.asp?ID=2331&sort=&pagenum=12&yrstart=1986&yrend=1990" rel="nofollow - 1988 BFN-sold "It's a Livin' Thing...What a Terrible Thing to Lose" ELO |
Posted By: 79nautique
Date Posted: July-22-2008 at 12:27pm
|
So we have a arrestor that is too talk, get a new one, modify the existing one, and we have a dist that isn't curved correctly and is way short on final advance and now you want to replace a carb again.
Sounds like you need to hire someone that know how to tune an engine and dial everything in because getting it close enough isn't working out for you too well. And jacking with the carb will never overcome the problems caused be the advance curve's profile, so unless you are willing to fix the curve profile your waisting your time d*cking with anything else. because your loosing power on the top end because there isn't enough timing for the engine. Hel just for the fun of it get it started add about 4-6 degrees more timing then go run it and I bet it runs much better on the top end, ease into the throttle as now you might have too much timing for the lower rpm's and it might ping. But this will demonstrate and prove to you that you need more timing for the higher rpm's and the only way to get that is by change the advance curve profile ok? ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=756&sort=&pagenum=1&yrstart=1979&yrend=1979 - 79 nautique |
Posted By: lewy2001
Date Posted: July-22-2008 at 12:28pm
|
Would have to check my old Holley book on carby sizing and V/E. Most stock engines only run about 85% VE. But considering a 351 cu in motor handles a 600cfm carby you would think that a 454 cu in which is approx a 30% increase in volume would require a 30% larger carby i.e. 780cfm carby.
I forgot it is GM so obviously wouldn't be as efficient as the blue oval hardware. 
What model was your 750 Holley. Was it a square bore or did it have extremely large primaries like q-jet. I think you should have been able to dial it in OK may have required some changing of jets & PV's. I think at one stage you said the vac secs were opening early. This may have been your problem. Possibly a stronger spring may have solved problem. Maybe to late now if you have ordered a 650cfm anyway. The smaller carb should give better economy anyway. ------------- If you're going through hell, keep going http://www.correctcraftfan.com/diaries/details.asp?ID=2999" rel="nofollow - 89 Ski <a href="http://www.correctcraftfan.com/diaries/details.asp?ID=5685" ta |
Posted By: BuffaloBFN
Date Posted: July-22-2008 at 12:45pm
|
I cancelled the order...Chris was right! I called back and got a different tech and pushed him a little for the details.
I'll get a handle on it somehow...in the meantime I'll keep you guys entertained by chasing my tail?!!? LOL Thanks again Chris!!! ------------- http://correctcraftfan.com/diaries/details.asp?ID=2331&sort=&pagenum=12&yrstart=1986&yrend=1990" rel="nofollow - 1988 BFN-sold "It's a Livin' Thing...What a Terrible Thing to Lose" ELO |
Posted By: GottaSki
Date Posted: July-22-2008 at 1:00pm
I agree the 750 is more appropiate but I dissagree regarding VE, the VE on the BBC will be vastly better than the SB ford. The BBC has canted valves and the valves and ports are more smartly formed and sized for top end. secondly, to send the " sh|tcan the small carb" idea home... An undesized carb will not automatically give better economy, he will be into the secondaries sooner in the throttle. this also gives less precise throttle control due to the vacuum actuation. thridly, the undersize carb can be harmful for the engine. say if the engine were to produce 2.5" of vacuum at WOT, this could shut off the PV and make it run 25% lean at max rpm and load, this could frag a piston. like has been suggested, one can't fine tune a carb till the timing is better addressed, and that would be difficult to do properly and safely with an undesized carb. ------------- "There is nothing, absolutely nothing, half so much worthwhile as messing around with boats...simply messing." River Rat to Mole |
Posted By: 79nautique
Date Posted: July-22-2008 at 1:19pm
|
But they curved it specificly for the cam profile so that it would have 24 degress at 3000 rpm and mine runs great,... oh sorry thought I heard Timmy crying sorry about that.
So maybe Tim can help you catch your tail since he talked you into the quality POS distributor you bought. ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=756&sort=&pagenum=1&yrstart=1979&yrend=1979 - 79 nautique |
Posted By: BuffaloBFN
Date Posted: July-22-2008 at 2:23pm
|
Thanks all for the input. I probably don't word things as well as can be, but I think it's 24 degrees of advance at 3000...so at 14 initial I have 38 total at 3000?
Tom, thanks for helping to look after me; I read what you have to say closely! You and Lewy make me think I have the right carb. Symptoms as follows... The 750 had the motor starting immediately where the 600 wants it to turn a few times before it hits. The 750 ran rich(sooty plugs) and stumbled at 36-3700 rpm's with a 7.5 PV and stumbled at 38-3900 with a 4.5 PV. The 600 runs up to 4100 but it feels like there should be more. It also stumbled out of the hole with 6 people on board, but behaves with 2 on board. I'm not the pro like yall, but my gut feeling there was that it was thirsty so we parked it after 1 run. The gas mileage has gone down drastically like Tom said. I haven't been running it much since the 600 has been on it...not much at all really due to break in concerns and what I've read here about running lean. All that said, I put the black(strongest) spring in the vacuum pot and put in a 2.5 PV. From here I'll do 1 thing at a time and see what happens. It may be a while before I report back(busy,busy), but thanks again for all the help!!! ------------- http://correctcraftfan.com/diaries/details.asp?ID=2331&sort=&pagenum=12&yrstart=1986&yrend=1990" rel="nofollow - 1988 BFN-sold "It's a Livin' Thing...What a Terrible Thing to Lose" ELO |
Posted By: eric lavine
Date Posted: July-22-2008 at 2:25pm
| Carbing is an art, I put 2 edelbrock 750 cfm and they dumped fuel down that thing, 383 cubes and the charts said no problem, i tried everything, i didnt want to go down to a 650 or 600 cause i felt it wouldnt supply the air i needed. for ***************s and giggles i purchased a Holley 780 and slapped her on, no jet changes just bolted it up, the engine came to life, i wouldve never thought it because i kept thinking the carb was to big...maybe it was i dont know....was it cubes or was it air flow? |
Posted By: 79nautique
Date Posted: July-22-2008 at 2:37pm
|
I would but the 750 back on get a real timing light and found out exactly what the timing is at idle, 1000 rpm, 2000 rpm and 3000 rpm and quit guessing what it is or what it is supose to be know exactly what it is by verify it,, engine tuning 101 kids that chase tails.
the stumble at higher rmp is because of the carb and it's settings/jetting/metering of the fuel/adjustments use smaller primary jets and the 2.5 PV in it so the secondaries don't kick in and flood it out or riching it up to early. To bad your not closer to Indy I'd have you dial in an a hour or two depend if you had the right jets or had to go get them. ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=756&sort=&pagenum=1&yrstart=1979&yrend=1979 - 79 nautique |
Posted By: BuffaloBFN
Date Posted: July-22-2008 at 7:42pm
|
Chris, I'll get a timing strip tomorrow. I have measured off of TDC with the tab as a reference and have some good #'s. I'll get the details for you.
Put the 750 back on and it starts right up...no laboring like the 600. It has 71 jets and the 2.5 PV in it and still stumbles at 3800. It did run up to 4000 the first time, but not again. It's also drinking fuel again...gotta be too big or messed up to begin with. Is the difference between the 650's on summit and jegs and what I need the reason SECC charges so much for the replacement 650? I'm just about over this after so many changes to the carb with very little change...time to put the 600 back on it and stay out of the top end. ------------- http://correctcraftfan.com/diaries/details.asp?ID=2331&sort=&pagenum=12&yrstart=1986&yrend=1990" rel="nofollow - 1988 BFN-sold "It's a Livin' Thing...What a Terrible Thing to Lose" ELO |
Posted By: eric lavine
Date Posted: July-23-2008 at 10:13am
|
you still need a miniumum of 18 inches of vacuum at idle, did you compare between the 750 and 600?
your playing the carb game, there is no way you can dial an engine in with 13 to 14 inches of vacuum, you need to get the engine to 18 and no less, whether you have a severe vacuum leak or carb size. its the same as you trying to dial in an engine with 50 lbs of compression, vacuum also pulls fuel into the 2 front cylinders and i would guess those 2 fronts are running a little lean or not as rich remember......what controls secondaries on your boat a a a compression? cable? solenoid? your wife sits by the carb and you tell her to open them up? first things first my friend |
Posted By: eric lavine
Date Posted: July-23-2008 at 10:25am
|
timing will not effect vacuum, unless you are a tooth off or your chain is stretched, restrictions create vacuum.
something as simple as a PCV valve will f-ck with vacuum, a good example was yesterday on a 5.7, the pcv sounded like a buzzard and the engine was shaking and the AC vents on the truck would not switch because they are controlled by vacuum, the computor sensed this. new PCV valve and cured the problem. once you plug a vacuum guage in and get the readings your getting you should of stopped right there to figure out why, get that cured and go on to the next step |
Posted By: eric lavine
Date Posted: July-23-2008 at 11:39am
|
Im hammering you, lol
what is the first thing the doctor does when you go there? and what are his 2 most important tools? a stethascope and a blood pressure guage. when he checks your blood pressure and its off the charts does he go on to the next step....no, if your heart is beating at 200 beats a minute, to the next step? no a compression guage and vacuum guage are nearly equal to these tools the doctor uses if your compression is bad are plugs going to cure the problem? no if your vacuum is low are plugs going to cure the problem? no Vacuum is as important as compression, with out either one the engine WILL WILL not run as it should, so take care of first things first |
Posted By: lewy2001
Date Posted: July-23-2008 at 11:58am
|
Greg dont give in so easily and opt for the smaller carby.
I think the 600cfm carby is just masking your timing curve problems better than the larger carby. In saying that it starts much easier on the larger carby suggests that the main jets may be a little large. 79 has hit it on the head until you know what advance you really have at 2k,3k & 4K you are only going on what the spec sheet says. It may be way outside of the claimed advance. Verify that the advance curve is good then fine tune carby to suit. Think of the positive side when you finally sort this out you will get even more enjoyment. Taking the easy (more expensive also) route of the smaller carb may also leave a lot of potential performance left behind. I find problem solving very satisfying almost fulfilling. It may explain why I work in IT there are always plenty of problems to solve. Often it isn't the knowledge or know how that fixes the problem but the logical step by step troubleshooting that finds the solution. That's my pep talk for the day. Now get on with it. Lets us know what you find ------------- If you're going through hell, keep going http://www.correctcraftfan.com/diaries/details.asp?ID=2999" rel="nofollow - 89 Ski <a href="http://www.correctcraftfan.com/diaries/details.asp?ID=5685" ta |
Posted By: GottaSki
Date Posted: July-23-2008 at 8:09pm
FAIL. If he's starting the boat on the mains, he's got bigger problems. Thats just not happening. Other than that your advise is spot-on ------------- "There is nothing, absolutely nothing, half so much worthwhile as messing around with boats...simply messing." River Rat to Mole |
Posted By: BuffaloBFN
Date Posted: July-26-2008 at 3:19pm
|
I now have the PCM replacement 650 and ran it with the DUI...same results but with much cleaner plugs. So I switched out the DUI for the mallory that was in it before...same results. I do need to adjust the floats in the 650 as I saw 1 primary dripping after shut off...maybe the secondary float is too low, but I've been through that with the other carb. ------------- http://correctcraftfan.com/diaries/details.asp?ID=2331&sort=&pagenum=12&yrstart=1986&yrend=1990" rel="nofollow - 1988 BFN-sold "It's a Livin' Thing...What a Terrible Thing to Lose" ELO |
Posted By: BuffaloBFN
Date Posted: July-26-2008 at 7:56pm
|
OK then, it's all lack of vacuum. Good call Eric. I sat in the back and opened the secondaries manually at WOT, and it ran as it should.
Where oh where did my vacuum go?!!? ------------- http://correctcraftfan.com/diaries/details.asp?ID=2331&sort=&pagenum=12&yrstart=1986&yrend=1990" rel="nofollow - 1988 BFN-sold "It's a Livin' Thing...What a Terrible Thing to Lose" ELO |
Posted By: boat dr
Date Posted: July-26-2008 at 10:02pm
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Cam timing has every thing to do with vacuum.When and where the valves open and close will have a large part in how much vacuum a motor produces.........Boat dr ------------- boat dr /diaries/details.asp?ID=4631 - 1949 Dart /diaries/details.asp?ID=1533 - 1964 American Skier |
Posted By: eric lavine
Date Posted: July-27-2008 at 12:32pm
|
exactly as Doc is saying, the intake stroke creates vacuum, the compression strokes creates....guess what? compression.
look at it this way, if you were a tooth off which i doubt you are, the piston will come down and start its journey up, if the valve is still open she will fall flat. also if you took your shop vac and put your hand over the end and completely closed it off the vaccuum increases, as you open your fingers the vacuum will decrease.....its the restriction that creates vacuum, there is nothing you can do electronically or fuel wise to create vacuum, basically it is controlled mechanically. as earlier stated i wouldnt try anything until that guage reads 18 to 20 inches of vacuum at idle whether it be cam timing, rings, carb or so on an engine will miss all day long with the kind of vacuum your seeing and thats why i said to you earlier, what controls secondaries......vacuum, low vacuum early open |
Posted By: BuffaloBFN
Date Posted: July-27-2008 at 12:49pm
|
I'm not sure what I think I saw when I said the secondaries were opening early on the 750. I was by myself and trying to drive, so who knows.
It is a low vacuum prob for sure. When I opened the secondaries by hand with someone else driving, it ran on up strong and sounded good. There just isn't enough to pull to open them at all the way it is now. I got a new pcv valve and will check a few simple things. If I don't find anything, I suppose I'll have to start taking it apart again. ------------- http://correctcraftfan.com/diaries/details.asp?ID=2331&sort=&pagenum=12&yrstart=1986&yrend=1990" rel="nofollow - 1988 BFN-sold "It's a Livin' Thing...What a Terrible Thing to Lose" ELO |
Posted By: eric lavine
Date Posted: July-27-2008 at 1:28pm
|
pop that 600 back on and check the vacuum, easiest things first, im not saying that is the problem but.....if you dont try it you will never know.
I go through this stuff everyday, I have a guy who comes around my shop all the time and he costs me nothing but money, he insisted the other day that a fuel pump was bad on a truck because he said the same thing happened to him, so i told him if i drop the tank removing all 30 gallons of gas, swap out the assembly and it doesnt work will you pay for the 400 dollar assembly? I logically troubleshot the thing and couldnt pick anything up on my scanner, the fuel psi guage was doing funny things, it took me 4 hours to figure out it was the psi regulator under the plenum point being, anybody can swap parts and eventually you will hit the nail on the head but in the meantime if i would of put a fuel pump in this thing i wouldve had to pay for it and the labor approach it like a see-saw, if that side goes down what will the other side do? |
Posted By: BuffaloBFN
Date Posted: July-27-2008 at 1:43pm
|
Maybe I'll tie a string to the secondaries and hold it over my shoulder for when I need WOT?!!? LOL ------------- http://correctcraftfan.com/diaries/details.asp?ID=2331&sort=&pagenum=12&yrstart=1986&yrend=1990" rel="nofollow - 1988 BFN-sold "It's a Livin' Thing...What a Terrible Thing to Lose" ELO |
Posted By: BuffaloBFN
Date Posted: July-27-2008 at 10:18pm
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Not much else to check...guess it'll go in the garage soon while I can still get it out... ------------- http://correctcraftfan.com/diaries/details.asp?ID=2331&sort=&pagenum=12&yrstart=1986&yrend=1990" rel="nofollow - 1988 BFN-sold "It's a Livin' Thing...What a Terrible Thing to Lose" ELO |
Posted By: BuffaloBFN
Date Posted: July-28-2008 at 11:18am
|
So, the sun came up on a new day, the boat is in the driveway, and the pumpkin is about to get picked again.
I pulled it this morning and had to drive a fair distance to a functional ramp. With the quiet of dawn and w/o all the racket of a day on the lake, AND with my wishful thinking kicked to the curb; I can only say that it doesn't sound right. I pulled the plug wires this morning 1 at a time, and I think it's only hitting on 5 cylinders. Is it possible for it to run at all with the wrong cam? I talked with my machinist quite a bit about the cam going in it, but I think he sold me the wrong one. I can't think of anything else that it could be...I think I've eliminated everything else. The other thing I thought about on my morning drive was that of all the little things that could have gone wrong or been done wrong....?!!?  ------------- http://correctcraftfan.com/diaries/details.asp?ID=2331&sort=&pagenum=12&yrstart=1986&yrend=1990" rel="nofollow - 1988 BFN-sold "It's a Livin' Thing...What a Terrible Thing to Lose" ELO |
Posted By: JoeinNY
Date Posted: July-28-2008 at 11:48am
|
Whoa where the heck have I been, I figured you were off living the Nautique life whilst I had been on shore, sorry to hear thats not the case. Before you get absolutely crazy are you 100% sure your plug wiring is correct. ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=1477 - 1983 Ski Nautique 2001 1967 Mustang 302 "Decoy" http://www.youtube.com/watch?v=cO5MkcBXBBs - Holeshot Video |
Posted By: BuffaloBFN
Date Posted: July-28-2008 at 12:02pm
|
Howdy Joe...yea, I'm busy earning my 'fins'?!!? <---Like earning your wings in aviation.
The wires are as stated on the engine tag. I've had the DUI and now the original mallory in it. I've also been through 3 carbs, but the root problem is low vacuum. It doesn't change with any of the above variables. ------------- http://correctcraftfan.com/diaries/details.asp?ID=2331&sort=&pagenum=12&yrstart=1986&yrend=1990" rel="nofollow - 1988 BFN-sold "It's a Livin' Thing...What a Terrible Thing to Lose" ELO |
Posted By: eric lavine
Date Posted: July-28-2008 at 12:14pm
|
if you think its cammed wrong you'll be able to pick that up on a compression test, the low vacuum is a sure sign that something is not quite right.
Why do you think you may have the wrong cam |
Posted By: JoeinNY
Date Posted: July-28-2008 at 1:14pm
|
Make sure you have the cylinders numbered right and know which direction the rotor is turning and then it should be.. 1-2-7-5-6-3-4-8 Stranger things have happened than for two wires to be switched. There are people running around with lower vacumn that what you have. It sounds like earlier you were putting heavier secondary springs in that carb, did you reverse that process and try it with a lighter spring? There are always mechanical secondary carbs as a last resort. ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=1477 - 1983 Ski Nautique 2001 1967 Mustang 302 "Decoy" http://www.youtube.com/watch?v=cO5MkcBXBBs - Holeshot Video |
Posted By: lewy2001
Date Posted: July-28-2008 at 1:17pm
|
If it was only running on 5 cylinders you would have very rough idle & you would not be getting anywhere near the 4000rpm you are getting at WOT.
You have verified the timing curve manually with timing light? I assume so but have not seen you confirm that in the post.
You mentioned earlier that the secs were opening too early now it seems you are saying they are not opening at all on just vacuum. Have you verified it is low vacuum with a gauge? One possibility is that your rings may not have bedded in correctly yet so compression & vacuum are both low. If so have you tried lighter springs in vac secs? An old trick that I have seen done that may help you troubleshoot this problem. Is a small nut & bolt in the slotted cam on the secondaries butterfly shaft so that at large throttle percentage it manually helps the sec's open. The primary shaft has a linkage that connects to the secondary shaft with the slotted cam. The small nut & bolt uses this linkage as a form of mechanical secondaries. Similar to your string over the shoulder idea. Hope this is of some help I have the feeling you are becoming frustrated. Maybe 79 will pay a surprise visit and sort it all out. Wish I was closer so I could lend you a hand often two heads working together helps. Bit like a dual core processor. ------------- If you're going through hell, keep going http://www.correctcraftfan.com/diaries/details.asp?ID=2999" rel="nofollow - 89 Ski <a href="http://www.correctcraftfan.com/diaries/details.asp?ID=5685" ta |
Posted By: BuffaloBFN
Date Posted: July-28-2008 at 5:24pm
|
Here are my compression #'s
1. 119 2. 118 3. 119 4. 112 5. 119 6. 118 7. 119 8. 112 ------------- http://correctcraftfan.com/diaries/details.asp?ID=2331&sort=&pagenum=12&yrstart=1986&yrend=1990" rel="nofollow - 1988 BFN-sold "It's a Livin' Thing...What a Terrible Thing to Lose" ELO |
Posted By: BuffaloBFN
Date Posted: July-28-2008 at 9:15pm
|
I re-verified dist rotation and firing order. The compression #'s mean the cam is right?
I did go down to the next to lightest spring in the vacuum pot the other day. I have the lightest yet to try, but I wish I understood the vacuum loss. 87(Jim right?) does your set up have a wedge plate with the pcv plumbed off of it? I think I'll take mine off a check the #'s...I'm sure it'll cause float probs, but that's par for this course. That leaves the intake gaskets and rings that may not be seated...right? ------------- http://correctcraftfan.com/diaries/details.asp?ID=2331&sort=&pagenum=12&yrstart=1986&yrend=1990" rel="nofollow - 1988 BFN-sold "It's a Livin' Thing...What a Terrible Thing to Lose" ELO |
Posted By: boat dr
Date Posted: July-28-2008 at 9:51pm
|
I see two problems that do not add up with a new motor.....
#1 low vacuum 13/15 in. is too low #2 low compression 120lbs. is too low Common to these two is the CAMSHAFT. I may be speaking out of turn here but. One other possibility is the offset on the piston pin/ wrist pin. But surely those were installed "bakards", which is normal for a reverse rotation motor. The PCM cam # RA 050015, and was told that this is a PCM special grind...Boat dr ------------- boat dr /diaries/details.asp?ID=4631 - 1949 Dart /diaries/details.asp?ID=1533 - 1964 American Skier |
Posted By: eric lavine
Date Posted: July-28-2008 at 10:17pm
|
i vote for the cam being somehow someway out of time or keyed wrong,
if you took a bare long block with nothing on it, no carb, no distributor , just an intake with the correct size restriction. and you spun it with a drill at the front (this is theory) at 600 rpms....you would pull 18 inches of vacuum the compression seems real low, but across the board. i would say your valves are opening to late or to early. there is something wrong with the cam or as the doc mentioned the pistons it keeps going back to vacuum but the compression ratio verify's it. I dont know what the comp ratio is for the BBC but i bet it is up close to 150 psi, and again a good (correctly running) engine willlllllllllll pull 18 inches of vacuum, if your intakes are opening to early while the exhausts are open it will kill the vacuum of the engine |
Posted By: BuffaloBFN
Date Posted: July-28-2008 at 10:45pm
|
Yep Eric, I think our good buddy the Boat Dr is on to something here. The reference marks on my pistons are all to the front...I went back and checked my pics. Looks like I'll have to get a cam from Woody as well.
I thought I had researched this before I started...live and learn. Hopefully it won't be a season ender. ------------- http://correctcraftfan.com/diaries/details.asp?ID=2331&sort=&pagenum=12&yrstart=1986&yrend=1990" rel="nofollow - 1988 BFN-sold "It's a Livin' Thing...What a Terrible Thing to Lose" ELO |
Posted By: eric lavine
Date Posted: July-29-2008 at 10:11am
| Dont worry Greg, I have done alot worse things to an engine than this, you hit a speed bump and its definitely not a season ender. start on a saturday morning and you should be on the water by dinner time |
Posted By: BuffaloBFN
Date Posted: July-29-2008 at 10:41am
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I don't mind taking it apart and putting it back together so much...I'm more concerned about the price of the cam and whether Amy will come after me with a wooden bat or an aluminum one?!!? LOL
Assuming things stay as they look now, I'll be turning the pistons around and changing the cam. new lifters? new rod bearings? new rings? If this engine is so specifically tuned, should I put the original intake back on? Maybe even ditch the roller rockers and put it all the way back to stock? ------------- http://correctcraftfan.com/diaries/details.asp?ID=2331&sort=&pagenum=12&yrstart=1986&yrend=1990" rel="nofollow - 1988 BFN-sold "It's a Livin' Thing...What a Terrible Thing to Lose" ELO |
Posted By: JoeinNY
Date Posted: July-29-2008 at 11:14am
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I dont know about this duck and cover strategy on a running boat, the cam being a gear tooth or two off sure but complete shot gun... I got to think about this where is the machine shop that was advising on all this now that the motor isnt quite what you would have hoped?
------------- http://www.correctcraftfan.com/diaries/details.asp?ID=1477 - 1983 Ski Nautique 2001 1967 Mustang 302 "Decoy" http://www.youtube.com/watch?v=cO5MkcBXBBs - Holeshot Video |
Posted By: 8122pbrainard
Date Posted: July-29-2008 at 11:32am
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Greg, What's going on with you and the machinest? Billy mentioned it plus Joe just mentioned it. I too am wondering why you aren't asking him about the Marine cam he put in. Being a marine but gear driven instead of chain, is is backwards??? ------------- /diaries/details.asp?ID=1622" rel="nofollow - 54 Atom /diaries/details.asp?ID=2179" rel="nofollow - 77 Tique 64 X55 Dunphy Keep it original, Pete < |
Posted By: BuffaloBFN
Date Posted: July-29-2008 at 11:44am
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I'm going to talk to him after I talk to Woody. The cam is gear driven; the crank is RR and the cam is standard but with the reverse firing order...or it's supposed to be.
The cam didn't come in a PCM box and I think it needs to. ------------- http://correctcraftfan.com/diaries/details.asp?ID=2331&sort=&pagenum=12&yrstart=1986&yrend=1990" rel="nofollow - 1988 BFN-sold "It's a Livin' Thing...What a Terrible Thing to Lose" ELO |
Posted By: eric lavine
Date Posted: July-29-2008 at 11:52am
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Jack chamberlin had one in stock, it was 280.00 i believe, lifters are cheap enough to replace with new, personally i would re-use the rod bearings and rings...thats me though, I dont think you have enough time on the engine. keep the rings in the same bore and the bearings on the sma spot on the crank
if your machinist recomended that cam i would definitely have a serious one on one with him...you paid him for his knowledge you shouldnt have to pay for his mistakes |
Posted By: JoeinNY
Date Posted: July-29-2008 at 12:23pm
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We totally talked about this in the early going the std vs reverse rotation thing I thought you were going to be straight, anyway heres my take on a couple of the problems. First on the pistons, you need to talk to the piston manufacturer before you go taking out the pistions. If they were PCM pistons then they would have offset pins, if they are not the offset pin scenario is less likely in which case the direction only matters if you have valve cutouts that are direction specific. Do not pull out and turn around the pistons till you find out for sure they have offset pins.
On Low vacuum/low compression you could still be in a too tight rocker arm scenario. If your pushrods are too long or the rockers too tight your exhaust valves could not quite close and cause all your issues. This would be apparent with a leak down type test where you use air pressure to pressurize the cylinder then listen for leaks out the exhaust or into the intake. Definitely give the machinist the opportunity to make it right before you tear all his stuff out and buy new and above all keep calm and open your wallet only as a last resort. ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=1477 - 1983 Ski Nautique 2001 1967 Mustang 302 "Decoy" http://www.youtube.com/watch?v=cO5MkcBXBBs - Holeshot Video |
Posted By: GottaSki
Date Posted: July-29-2008 at 12:28pm
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I've just been taking this all in..
qvestion..did you open the throttle when testing compression? Or leave the butterflies closed? Hopefully the former not the latter. Low vacuum at idle is a suspicious symptom, but you must verify that that is the max vacuum you can get by turning the distributer for best timing at idle. Turn til vacuum fails to rise. If after a reset on the idle speed and air screws If its still below 16"-17" I'm with you, something could be very amiss with the cam. I think there is some confusion regarding he secondaries operation. the vaccum you see at idle does not operate the secondaries. At WOT there is no vacuum. But the secondaries are not a normally-open mechanism (they don't operate on the bench)....where does the vacuum come from? I believe its venturi vacuum... meaning you need significant airflow throught the carb to generate the venuri vacuum to operate the secondaries. this also suggest the engine is just not pumping the air is should be, and this may point to he cam again. I agree talk to your rebuilder. Consider taking the front cover off and verify the gears' alignment marks line up and/or see if the builder did some funky things with offset keys or dowels. There is also a remote chance that all the carb and timing issues fould a plug or two that can't recover and clean itself. I've seen it before and took the front cover off an engine for nothing looking for a stretched chain and it was just a freakin bad plug. ------------- "There is nothing, absolutely nothing, half so much worthwhile as messing around with boats...simply messing." River Rat to Mole |