Help! High Throttle hesitation
Printed From: CorrectCraftFan.com
Category: Repairs and Maintenance
Forum Name: Engine Repair
Forum Discription: Engine problems and solutions
URL: http://www.CorrectCraftFan.com/forum/forum_posts.asp?TID=41150
Printed Date: October-07-2024 at 12:27am
Topic: Help! High Throttle hesitation
Posted By: Dreaming
Subject: Help! High Throttle hesitation
Date Posted: May-30-2017 at 2:04pm
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So I put hour number 2 and 3 on the new motor this weekend... Motor starts like a Swiss watch, half a revolution on the starter and it just purrs. We spent lots of time varying the RPM in the low range (1500-2500 RPM) as I am still seating rings and just overall watching things to make sure it's right. Everything felt good, until we made a reasonably hard run and I gave ~ almost full throttle. We ran hard up to about 42 on the air guide for about 30 seconds, and then the engine started to feel like it loaded up, and bogged down. I pulled it back to idle speed, and ran up to about 2000 RPM with normal response, 2500 or so, the engine sputtered like it was flooding out. hammer the throttle and it bogged, and then felt like it started to come out. We have a Wake the World event that I am trying to be ready for in June, so I need to solve this issue quickly. Where do I start? |
Replies:
Posted By: KENO
Date Posted: May-30-2017 at 3:51pm
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Need a little refresher here, this is what a pro tec to distributor and Holley carb conversion.? What's the condition of the carburetor? |
Posted By: Dreaming
Date Posted: May-30-2017 at 4:08pm
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Hi Ken, thanks for the response. My original engine was a Protec, with TBI, all of it was junk after being left out in the weather with the engine cover up for a couple of rainy seasons. I replaced everything last year with a 351w standard rotation, roller cam, with Edelbrock RPM intake. Carb is 4160 Holley, and the distributor is a DUI. Carb was from another member here, but it was supposed to have been rebuilt not long before I bought it. I suspect the carb may be the problem, but I am guessing at this point. |
Posted By: KENO
Date Posted: May-30-2017 at 4:11pm
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I'd suspect the same and make a guess that when the secondaries are open that's when your problems start. I think I'd take it apart for a clean/rebuild as a starting point |
Posted By: Dreaming
Date Posted: May-30-2017 at 4:20pm
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Thanks Ken, I have a rebuild kit at home just in case... I guess I will pull it and try to rebuild it this week. is there anything I should be looking for? |
Posted By: KENO
Date Posted: May-30-2017 at 4:45pm
Hey, at least you're prepared  I'd just have a good manual/set of instructions but look closely at secondary related items especially, just as a hunch. Cleanliness is your friend. Plenty of people here with Holley experience to help out with any questions Don't know if you have a clutch headed screwdriver for the secondary metering plate, they're not real easy to find but you can "hack" your way through the job with a flat blade of the right size. You made it this far, you're almost there |
Posted By: Dreaming
Date Posted: May-30-2017 at 5:54pm
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yep, I have a clutch blade, I did the Holley carb on my 82, and it ran afterwards, Just have never experienced a high end stumble like this one. Thanks for the help and encouragement I am definitely ready for a trouble free day on the water, getting to the water seems to take an act of God... it's definitely frustrating to have problems once we're there. I keep having to remind myself that it can all be fixed, and I'll eventually get there. |
Posted By: TRBenj
Date Posted: May-30-2017 at 6:10pm
| New cam or reused? Not sure this sounds like proper engine break in procedure. |
Posted By: Jonny Quest
Date Posted: May-30-2017 at 9:49pm
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Sure does sound like carb issues. First thought is that the secondaries are not opening correctly. Second thought is that the power valve could be bad. Per Holley: "Holley carburetors have a power enrichment system that provides fuel to the main power circuit during heavy loads or under full throttle situations. The vacuum operated power enrichment system is controlled by a Power Valve that times the operation to your engine's specific needs." JQ ------------- Current 2003 Ski Nautique 206 Limited Previous 2001 Ski Nautique Open Bow 1994 Ski Nautique Open Bow Aqua skiing, ergo sum |
Posted By: Dreaming
Date Posted: May-31-2017 at 2:32pm
New, Roller cam. I was told by the engine builder that the first 20 minutes of run time were the important part, I followed their instructions for that break in period. I know there are several schools of thought on engine break in, but I would be interested in hearing where you feel I am going wrong, and what to do differently. I only want to do this engine replacement task once.  I am running Joe Gibbs break in oil, and have ~2-3 hours on the engine. Update on the carb situation: I pulled it apart last night, and began the cleaning process. I soaked all the parts in carb dip, and everything looked pretty clean. I blew the orifices of the main body out with air, and a chunk of black goo came out of one of the secondary orifices, so good possibility that was the problem. I did notice that many of the fasteners were barely finger tight, and that the main jets(?) on the primary side were loose. Unfortunately one for the alignment pins on the primary metering block fell on the workbench when I took the plate off, so I am going to see if I can find a new metering block as a replacement. I also read up on power valves, there is a 2.5 in the carb kit, but from the way I understand it, I want to move to a 4 or 6.5 with my upgraded intake manifold? I do not intend to go further with upgrades, but with the free'er intake I need a higher number valve, correct? I appreciate fuel economy, so I am thinking the 4 is probably a good compromise with correct mixture at the higher throttle positions, but not changing the fuel mixture too early. |
TRBenj wrote:Posted By: KENO
Date Posted: May-31-2017 at 3:14pm
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I'd always been a 5.0 or a 6.5 PV guy myself, but there are plenty of 351's running around with 2.5 PV's too. Things change Most Holley's for marine 351's had 65 or 66 mains and the secondary metering plate was stamped with a number like maybe for example a 3 or a 6 or a 36 that when you look up the info will tell you the main hole and idle hole sizes. What's the list number on the air horn? I could tell you quite a bit about what it should have for jets etc from that. I've put a carb primary metering block on with only one of those pesky little pins and if you line things up carefully it works. They're usually really tight in the metering block edit, they're cast in when the metering block is cast Loose main jets would screw things up and that glob of junk couldn't help things any. |
Posted By: TRBenj
Date Posted: May-31-2017 at 3:25pm
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Roller cam, good. Post cam break in (not needed for roller- flat tappet only), you want to set the rings. You want to load/unload the engine pretty good right off the bat. Don't stay at any rpm for very long- avoid idle (once warm) and no prolonged wot. Constantly varying the throttle is good, but don't be trying to keep the rpm way low. Fuel/cooling/timing needs basic sorting before you begin, of course. |
Posted By: KENO
Date Posted: May-31-2017 at 3:39pm
Can't let this slide by
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Posted By: 1980nautique
Date Posted: May-31-2017 at 3:40pm
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Kris, I would use the proven method of Holley power Valve selection!!! The starting point is to check manifold vacuum at idle on a warmed up engine. Divide this number in half. ex. 13 hg.'s at idle divided by 2= 6.5. A 4.0 hg. power valve will slam shut at 4.1 hg.'s and begin to lean out the fuel mix as the engine recovers vacuum and RPMs at WOT. Recommend putting in the 6.0 or 6.5 hg. Power valve that comes in the 4160 Holley marine Kit. I don't believe you will find a marine based Carb Kit for a 4160 Holley that comes with a 2.5 hg. power valve Compared to the street version the Power valve, Main Jet sizes and the J Tubes are the main difference in the Marine Carburetor,.Keep us informed!!!! |
Posted By: Dreaming
Date Posted: May-31-2017 at 3:45pm
Ken - I don't have the list number here at work, but I can post it later  good to know on the pins... Is their only function to align the gasket? the rest of the metering block looks good... it's not got further damage anyway. |
Posted By: KENO
Date Posted: May-31-2017 at 3:49pm
I don't believe you're right It's hard to find a later model 600 cfm marine Holley 4160 with something other than a 2.5 PV as the original PV. Earlier ones a 6.5 was common You should clean your !!!!! key too by the way |
Posted By: KENO
Date Posted: May-31-2017 at 3:50pm
It keeps the idle passages lined up too but being careful you can get it right. |
Posted By: Dreaming
Date Posted: May-31-2017 at 4:03pm
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Tim - thanks for advice. I did set timing etc, and will check it again once I reinstall the carb, and will also dial in the carb with a vacuum guage once it is re-set. Cooling is working well, all systems were normal during my lake run on Monday. I have followed the school of thought that rings need seating at all ranges of RPM, when new, so I'll adjust my speed expectations and run a little faster to make sure we set the rings correctly, but will not baby it so to speak. 1980 - sounds like good advice... no Idea where my vacuum numbers are right now, so I guess that you are suggesting I install the 2.5 that came in my kit and replace once I have accurate vacuum numbers? |
Posted By: KENO
Date Posted: May-31-2017 at 4:42pm
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Post your list number later and I can probably tell you what it originally came with.assuming your list number is in my Holley manual. You'll probably notice that me and 80SN and probably a whole bunch of others like a 6.5. Your idle vacuum should be over 13. Sometime back the Holley engineering department decided to build 600 cfm 4160 marine carbs with a 2.5 PV and I've had genuine Holley marine kits come with a 2.5 that I've replaced with a 6.5. I figure their engineering dept is pretty smart and they had their reasons My guess is slightly better fuel economy And by the way vacuum never recovers till you back off the throttle 1980 nautique Your boat isn't a car cruising on the highway |
Posted By: 1980nautique
Date Posted: May-31-2017 at 4:48pm
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Kris, cut and paste this address: "http://documents.holley.com/techlibrary_carb_numerical_listing.pd" into your browser. and use your LIST # and verify required Power Valve. Does the Carb have "J" tubes on the bowl vents? |
Posted By: 8122pbrainard
Date Posted: May-31-2017 at 6:55pm
A good hardware store should have one of those boxes of assorted dowel pins. Probably back at the service desk. ------------- /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: KENO
Date Posted: May-31-2017 at 7:37pm
Hey thanks for the chart I've got 7 marine 600 cfm 4160's either on boats or on the shelf You might call me a hoarder or maybe somebody who likes spare parts First one is a 6576 list number not on the Holley chart, it's old (from 1976) it's always had a 6.5 PV since it was new Continuing on list number 50419-1 (have 2 of them) 2.5PV List 9392 2.5 PV List 7163 2.5 PV List 80319-1 2.5 PV and last but not least a list 75009 with a 6.5 PV And all those PV numbers are from the Holley chart |
Posted By: KENO
Date Posted: May-31-2017 at 10:01pm
The one I had to assemble with one pin was because the pin broke off and after looking at a metering block today, it's pretty safe to say that the "pin" is part of the casting and somebody did some "creative engineering" to drill a hole and put a new pin in Dreaming's metering block. Seems like it wasn't a very good fit since it fell out. |
Posted By: Gary S
Date Posted: May-31-2017 at 10:05pm
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When I talked to Holley's tech line a few years ago they told me they purged alot of the older carb info when they computerized ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=1711&sort=&pagenum=1&yrstart=1966&yrend=1970" rel="nofollow - 69 Mustang HM SS 95 Nautique Super Sport |
Posted By: Jonny Quest
Date Posted: May-31-2017 at 11:48pm
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As another point of reference -- my QuickFuel M-600 is based on the Holley 4160 design. It came from the factory with a 6.5 power-valve. JQ ------------- Current 2003 Ski Nautique 206 Limited Previous 2001 Ski Nautique Open Bow 1994 Ski Nautique Open Bow Aqua skiing, ergo sum |
Posted By: GottaSki
Date Posted: June-01-2017 at 10:50am
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The whole 2.5 pv never made sense to me when they made that switch, especially to old list rebuild kits that used to come with a 5.5 or 6.5. To have to wait til the vacuum is less than 2.5" before the carb switches from lean cruise to high load, only induces a distinct dull flat spot when you mash it. ------------- "There is nothing, absolutely nothing, half so much worthwhile as messing around with boats...simply messing." River Rat to Mole |
Posted By: Dreaming
Date Posted: June-01-2017 at 4:29pm
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Hmmm. lots to think about. We had a bit of a crazy night last night, so I wasn't able to get to the garage to pull the list number. I will pull it today and repost. On the metering block pin, it was once molded into the carburetor, but must have been either cracked/weakened, or I broke it getting the metering block off. I did talk with my local machine shop/speed shop on the way home from work last night, and he said he would reuse the metering block with only one of the alignment pins as Ken stated. On the PV discussion, I hope to read a bit more, but for the moment, it sounds like I should install the 2.5 and then take some vacuum readings. Seems like the vacuum at idle seems funny because that is not when the PV is used, but I can take the reading and report for sure... then you smart guys can help me to size it correctly. |
Posted By: Dreaming
Date Posted: June-01-2017 at 11:54pm
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Alright, There 3 sets of numbers on the horn of the carb, they are: FIJL-CA 50469-1 3492 I believe the list # is the 3492, but not too sure at this point. I may try and start assembling tonight, likely going to be tomorrow evening. |
Posted By: KENO
Date Posted: June-02-2017 at 12:28am
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50469-1 is the list number. The link a handful of posts ago only lists a 50469 but I have a paper list that does have the 50469-1 It's a 600 cfm with 65 main jets, and a 2.5 power valve. If you have the number from the secondary metering plate, I should be able to tell you some info on that. It's just a number cast into the plate like a 5 or 6 or 34 just for example. There are a lot of different numbers. I'd put it together with what you have (2.5) and get a 5.0 or a 6.5 to try later if you feel like it You did find issues so with those corrected maybe your problem will be resolved You could also get a couple of 66 main jets to try if you're buying parts
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Posted By: Dreaming
Date Posted: June-03-2017 at 9:09pm
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So I re-assembled the carb last night and just spent a couple of hours putting everything back together. I reset the timing at 11°BTDC at 600 RPM. then adjusted the carb idle needles for 16.5-17" vacuum (600 rpm). I'll have to wait until tomorrow to throw the boat in the water, but it is running on the hose. I hope all is well on the top end now, it does start good, and seems to idle nicely. I did check the idle mixture screws, and they will make the engine die if I get them too far in, so we're running on the idle circuit at idle. One more fun fact for Ken The secondary plate seems to have a 59 stamped on it. the five is pretty lightly stamped, but I think that was the correct number. |
Posted By: KRoundy
Date Posted: June-03-2017 at 10:08pm
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Best of luck! If I ever need to work on my carb I'll be pulling it and taking a trip down to your house. Let us know how it does. I'm guessing that black goo removal did the trick. ------------- Previous: 1993 Electric Blue/Charcoal Ski Nautique Current: 2016 Ski Nautique 200 Open Bow |
Posted By: KENO
Date Posted: June-03-2017 at 11:01pm
Not a lot I can tell you about that plate except that it's the stock plate for a fair number of marine 4160's and info on it is not very easy to find. I have one on a 4160 that feeds a 351 with gt-40 heads with no problem at all. Probably looked just like this 
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Posted By: Dreaming
Date Posted: June-04-2017 at 2:03am
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Kevin, It didn't take as long as i expected, I think I could do another one pretty quickly as well if you ever need it. Ken, your correct, mine looks just like that. Thanks for all of your guidance on this. hopefully the water test goes well tomorrow! |
Posted By: KRoundy
Date Posted: June-05-2017 at 10:04pm
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Well? Any fun video to post? Kevin ------------- Previous: 1993 Electric Blue/Charcoal Ski Nautique Current: 2016 Ski Nautique 200 Open Bow |
Posted By: Dreaming
Date Posted: June-07-2017 at 4:00pm
nothing yet... Main breaker failure at the boat ramp kept me from testing the carb. I have a replacement intended to arrive this afternoon in the mail... Hoping to have it installed and up for a re-test on Saturday. |
Posted By: MrMcD
Date Posted: June-07-2017 at 5:32pm
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Kris, I am not a carb guy but your comment on Timing caught my attention. You mentioned timing at idle. That is a good start but the important timing to measure is what you have at 2,500 rpm up to 4,000 rpm. Watch the timing mark move as you advance your rpm. It should advance smoothly as your rpm increases and max out around 35 degrees usually between 2,500 and 3,000 rpm. The max or total timing number is the one that will give you performance or melt your engine. If your distributor allows say 40 degrees at 3,000 rpm that is very dangerous for your pistons. The only solution would be to recurve your distributor or back off the idle timing setting till your max is proper. If your timing does not advance smoothly, if it jumps or does not move at all you need to go inside the distributor and repair it. If your distributor as it is set now at 11 degrees is only at say 30 degrees at 3,000 you are leaving power on the table. You can add idle timing to move your 3,000 rpm timing up or get the distributor re curved. Others that know the 351W better can give a better idea of the exact timing curve preferred but in general this is what you need to be aware of. There are two ways to verify this. Any speed shop sells timing tape that you put on your harmonic balancer or you can measure exactly how far it is from 0 - 10 on your boat and add a new line at 20,25,30,35, The easy way is to use a Set Back Timing light that allows you to dial in how much timing you want and use your normal timing marks. These are available for $80 or so and help. I hope it purrs next time out. ------------- |
Posted By: Dreaming
Date Posted: June-07-2017 at 6:14pm
| Hi Mark, I have a set back timing light, and will check the total advance. The bottom of the distributor is marked 24° @ 3000 RPM, so I used that as my guide (new DUI distributor) to achieve an assumed total timing advance of 35° (11° initial). Without the engine running well in the water, I haven't been able to check timing under load, but I would like to do that as soon as I can. Thanks for the suggestion! |
Posted By: MrMcD
Date Posted: June-07-2017 at 6:29pm
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Timing is rpm driven, it can be verified while running on the driveway in about 2 minutes. It sounds like you should be I I good shape but verify for peace of mind with your brand new engine. ------------- |
Posted By: Bri892001
Date Posted: June-08-2017 at 12:12am
| Could this be a fuel flow issue? Something like a plugged fiuel filter or anti-siphon valve? |
Posted By: Dreaming
Date Posted: June-10-2017 at 8:56pm
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So I am happy to report that it was a great trip to the lake this morning... I was able to take 45 minutes on the ramp since I had the whole place to my self. I checked ignition timing and found that it was accurate at 3000 RPM, ( 35°) and my 11° was good as an initial timing set point I think. I also was able to work through the throttle/trans lever adjustment that I have been unhappy with. Power was good with the replaced main breaker, so I launched the boat and spent about 2 hours of run time on the lake. The throttle hesitation is definitely gone, and I varied the RPM from 1500 to ~4000 without spending too much time at any one RPM. The carb rebuild was a good suggestion, and helped a lot Thanks to KENO and the others of you that chimed in. I liked the way the motor started better before the carb rebuild, now it takes a couple of throttle pumps at the ramp to get it to start cold, but I also noticed that the choke opens very quickly, so I may need to read up on delaying the opening a bit. Over all, I am pretty happy. I still have a little bit of a drive line vibration, but I suspect that is a prop issue. I guess I will work through solving that as well, but it will likely take a back seat to the next few hours of boating time and getting the engine broken in. |
Posted By: Jonny Quest
Date Posted: June-11-2017 at 12:46am
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Nicely done. Gotta love finding and fixing a problem. ------------- Current 2003 Ski Nautique 206 Limited Previous 2001 Ski Nautique Open Bow 1994 Ski Nautique Open Bow Aqua skiing, ergo sum |
Posted By: KRoundy
Date Posted: June-11-2017 at 1:39pm
Well done, Kris!  ------------- Previous: 1993 Electric Blue/Charcoal Ski Nautique Current: 2016 Ski Nautique 200 Open Bow |
Posted By: Dreaming
Date Posted: June-11-2017 at 6:32pm
Thanks Kevin and JQ glad it is finally coming together! |