Engine won't pull more than 4,000rpm
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=21914
Printed Date: November-19-2024 at 1:46pm
Topic: Engine won't pull more than 4,000rpm
Posted By: MAN - GA
Subject: Engine won't pull more than 4,000rpm
Date Posted: June-01-2011 at 12:02pm
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Here is what I have done to my 75 Mustang w/ 302 (stock) over the winter - just throwing it all on the table in hopes maybe someone has a suggestion on what I am missing
1. Replaced strut and prop (Acme 1210) had shaft runout checked and less than .001 and lapped in new prop and aligned per CCF posts. Replaced packing log hose, and remachined coupler flange on shaft due to PO breaking the flanges apart with screwdriver. 2. Rebuilt carb myself with Holley kit # given to me by Holley tech from air horn numbers - clearance on Acc. pump is per Holley instructions 3. Replaced timing chain w/ double roller and installed new 143* thermostat 4. Sent original distributor to Mallory to rebuild and since they didn't have specific parts they sent me a new points distributor (24* mech. advance) 5. Pulled fuel cell and cleaned inside, new vent lines, new fuel fill hose/cap assembly, cleaned and new O-ring on anti-siphon valve, new CG approved fuel hose & filter changes 6. New mechanical fuel pump 7. Replaced coil and ballasts have all correct voltage 8. New battery, battery cables, cleaned starter/alternator wiring connections and used di-electric grease on terminals 9. New impeller, replaced hose on all cooling/freshwater pickup, and pulled resealed thru-hull nipple for freshwater pickup Here is the two issues I am noticing. 1. When I come off idle in hard acceleration I get a little hesistation and then it takes off hard and strong - Acc. pump shoots a nice continuous shot and there is not any issues on top end at WOT like it is starving for fuel keeping me from getting more than 4,000rpm 2. I set initial timing at 10*btdc and ran to WOT and couldn't pull more than about 3,600rpm on two different tachs. I then drove at WOT and turned the dist till it started to lose power and then locked it down - when I rechecked initial it was at 18*btdc with no starting issues and checking with a digital timing light I am getting 42* total at 3,000rpm My top end speed came down from the mid-high GPS speed of 47-49mph to about 40-42mph with the new prop and I used to pull around 4,400rpm Is the new prop causing such a drastic change or am I missing something in the tune-up process |
Replies:
Posted By: GottaSki
Date Posted: June-01-2011 at 12:12pm
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42 degrees total is historically too steep for a 302
Its mostly a matter of combustion chamber, compression, and rod/stroke ratio. 38-40 degrees should be maxed. Set your air screws for strongest smoothest idle while in gear. the load on the engine is critical to set them right. That flat spot off idle should dissapate afterward. If it doesn't, and the dull spot is a little higher in the rpms like 2 -2.5k when you dump the throttle we'll have to talk about the PV. 302's like to spin to make hp, short stroke = no spin, no power. So now tell us about this prop, and the old one., since it is suspect. ------------- "There is nothing, absolutely nothing, half so much worthwhile as messing around with boats...simply messing." River Rat to Mole |
Posted By: 8122pbrainard
Date Posted: June-01-2011 at 12:33pm
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Mark,
I don't feel it's the prop. That engine should have no problem turning a 12.5 X 12 prop at a higher RPM. ------------- /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: TRBenj
Date Posted: June-01-2011 at 12:41pm
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Yup, not prop related... Im spinning my 1210 4500 RPM (45mph). The 12x14 and 12x15 Federals were good for about the same speed at 4200.
Something is definitely goofy with the fuel and ignition. Dumb question- did you set the dwell properly? ------------- |
Posted By: MAN - GA
Date Posted: June-01-2011 at 12:52pm
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I had the same feeling on the total timing as well. I did not check idle vacuum in gear when setting idle air mixture I did it in neutral - would this contribute to why I have noticed it running a little rich - my plugs have a little dry soot on them on the insulator - there is no oily residue and the electrode ends are not wearing unevenly or prematurely
The old prop was a 12x13 or 12x14 Federal - I think I remember TRBenj saying in older posts that most of these boats had the 12x14 Federals originally, the only problem I have is reading if the pitch number is a 13 or 14 - I am about to send the old prop back to Delta for refurbishing and maybe they can confirm for sure. The new prop is the Acme 1210 which is 12.5x12 with a .060 cuped blade |
Posted By: MAN - GA
Date Posted: June-01-2011 at 12:54pm
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dwell is right at 27 double checked with two different dwell meters - Mallory spec sheet they sent me back says 25-29
point gap is .019 if I run the specified point gap of .018 the dwell sits 25 and I wanted to be in the middle of the range |
Posted By: Bri892001
Date Posted: June-01-2011 at 12:57pm
| Are you pretty sure your secondaries are opening on the carb? |
Posted By: MAN - GA
Date Posted: June-01-2011 at 1:20pm
| the linkage operates fine and the diaphragm is new - I can run it and then stop and check for the throttle plates on the secondaries being wet and they are - I have not had an opportunity to have a friend drive and me watch the secondary operation during acceleration or WOT to verify visually during power though - this is on my checklist, but I would think if the secondaries weren't opening I wouldn't be able to make the RPM I am |
Posted By: TRBenj
Date Posted: June-01-2011 at 1:25pm
The secondaries should be coming in between 3500-4000 RPM, so its quite possible that theyre not actuating- or at least not actuating all the way. Ive seen this happen with brand new diaphragms, so I can only assume something in the vacuum/venturi set up was plugged. I would bump this to the top of your list to verify before we go on a wild goose chase... it seems you have covered most of the usual basics already. ------------- |
MAN - GA wrote:Posted By: MAN - GA
Date Posted: June-01-2011 at 2:04pm
| I agree and thanks guys for the input I needed a refresh in my process of elimination to double check myself |
Posted By: eric lavine
Date Posted: June-01-2011 at 6:09pm
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you got all the right conditions for a tornado, but it aint happening.
steer from the accelerator pump, that gets you going, i agree not that it matters that something is up with the secondary circuit, get back there and watch them. ------------- "the things you own will start to own you" |
Posted By: MAN - GA
Date Posted: June-06-2011 at 12:08pm
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You guys were right and the secondary is not opening up - it comes open maybe 25% at WOT and with my daughter driving and me engaging the linkage by hand I can get the RPM up to around 4,500. I pulled the diaphragm and spring out and nothing is out-of-place and the gasket b/w carb body and diaphragm body is in place and seated properly. I am at a loss on why the butterflies won't fully engage - the port to venturi body is clear and I cleaned it again. The shaft the butterflies rotate on are not binding and move very easily
Any other suggestions or is this just a tired carb after almost 30yrs |
Posted By: Bri892001
Date Posted: June-06-2011 at 1:13pm
| Is that the original secondary spring and everything? If its new, it could be stiffer than your old one? They make different ones. |
Posted By: MAN - GA
Date Posted: June-06-2011 at 2:59pm
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original spring - only thing new was the diaphragm - I have already looked for a lighter spring - just don't understand since it ran fine last summer with the same spring
when I turn them by hand there is a huge flow of gas so I know the secondary metering block is working OK the butterflies just don't want to open far enough to get the additional gas needed |
Posted By: Luchog
Date Posted: June-06-2011 at 10:23pm
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Was the carb performing before your rebuild? ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=2095" rel="nofollow - 1980 Ski Nautique Commander 351W |
Posted By: MAN - GA
Date Posted: June-27-2011 at 1:26pm
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I have been doing some tuning and am still hitting road blocks. I got a quick change Holley cap for the secondary diaphagm so I could test different springs, but in trying different springs I don't get any additional RPMs out of the motor. The secondary is opening up, but not all the way - is it possible I may be getting some air leaking past the throttle plate shafts through the carb body which is decreasing the vacuum generated to pull on the secondary diaphragm?
I am also having issue with hard throttle from idle and have adjusted the acc pump for better results, but it is still coming with some hesistation Timing, dist. advance, fuel delivery, all are OK. If I turn over the secondary manually I can get the motor to pull the additional RPMs - I have had two tachs reading the same so I don't think I am getting erraneous readings Any suggestions? Carb is 30yrs old by the way |
Posted By: MAN - GA
Date Posted: July-20-2011 at 2:00pm
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I wanted to followup on this post and report that I found the problem. I called Boat DR (thanks Billy for the long discussion) and the issue was not carb related after all. I guess when trouble shooting sometimes you need to clear your mind and just go back to basics and check everything from A to Z. What I found was low voltage to coil and tracing back the wiring there was a loose connection at the ballast resistor - go figure it was this simple.
By the way TRBenj I am now getting the same results as you indicate with the ACME 1210 - I can get 4,600RPM with me in the boat (3/4 tank of gas) and a verified by GPS speed of 46.3MPH on smooth water with only a slight wind chop (wind about 3mph) |
Posted By: TRBenj
Date Posted: July-20-2011 at 2:50pm
Just to be clear- you confirmed that the secondaries were not opening properly, but you'd get your performance back if you opened them manually... and somehow that was due to a loose wire on the ballast resistor? After you had already confirmed you had good spark and timing? Im glad you went back to the beginning and started fresh, but Im trying to wrap my head around that one. 46mph @ 4600rpm is consistent with what I see on my Skier, but mine seems to be a relatively underperforming motor. Ive never seen anything better than 47mph with any of the props Ive tried (Federal 12x14, 12x15, OJ 12x13, Acme 1210). If you saw closer to 48-50mph at one point with another prop (which is not atypical for this hull/engine combo) then you may still be leaving some performance on the table. The 1210 should be every bit as fast as the other props- at least it was on the 49.x mph Mustang I tried them on. ------------- |
Posted By: MAN - GA
Date Posted: July-20-2011 at 3:32pm
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More clarification is needed...
First problem was the carb, but in hindsight this I think was just getting it tuned right after the rebuild. I changed out the secondary springs at the recommendation of Holley Tech after the carb rebuild I know this helped as I went to light and had them opening too soon. I finally found a good combination with 1x step lighter spring and seemed to have solved the secondary issue, but during this time I started getting diminished top end power even when opening by hand. After getting more frustrated I went back and checked everything on carb/ignition side to find the ballast resistor wire loose which I can only assume was vibrating loose as I was solving the secondary issue. Nonetheless I feel like I am getting good performance now from a motor that has around 1,600hrs on it As for the speed issue I am comfortable with the 1210 prop combination - the hole shot is 100% improved and I don't have any problem dropping the speed down a few MPH, but I have only taken one WOT speed pass thus far Thanks for all the input |
Posted By: TRBenj
Date Posted: July-20-2011 at 3:38pm
Now that explanation makes a lot more sense.
My point was that the 1210 has definitely been the best holeshot prop Ive tried, but at the same time, it has not sacrificed any top end on the 2 boats Ive tried them on. I *suspect* that if you were were to run your old prop again, you may find youre still running in the 46mph range. If indeed you had a legit 48-49mph before, then you should see it again with the 1210, all else being equal. If you can only muster 46, then something else may be wrong. ------------- |
Posted By: MAN - GA
Date Posted: July-20-2011 at 11:27pm
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I have had the old prop packed in a box for about 3mn and have not taken the time to get it shipped back to Delta for a little cleanup - might need to break the box back open in the early fall and go to the lake by myself and run them both some morning when things settle down and I can get some calm water for a change. My only speed run with the 1210 was about 8:30 in the evening on a weekday night. Summertime on Lake Lanier is not the best place for speed runs with all the traffic.
Thanks and I will report my findings when I can get some comparisons |
Posted By: Jllogan
Date Posted: October-13-2011 at 2:24pm
Mark, what did you do to test this? what should the voltage be? Do you check while running or just with the key on? ------------- http://correctcraftfan.com/diaries/details.asp?ID=5792&sort=&pagenum=1" rel="nofollow - 1986 Ski Nautique 2001 |
Posted By: MAN - GA
Date Posted: October-13-2011 at 2:45pm
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multi-meter and key in "on" position with a sheet of paper in hand writing down voltage as I went from key back to engine
after not being able to figure it out and starting over again the second time I put my hands on each wiring connection to check it and this is when it wiggled and I figured it out |
Posted By: 74Wind
Date Posted: October-13-2011 at 10:56pm
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Nice boat! I live in Peachtree City and keep a 74 Southwind on Oconee.
I see you do most of your own work, I can handle the simpler stuff but beyond that no one on Oconee knows a thing about old boats. I've also got a 75 Century Mark II, and have had some excellent work done at Lakemont Marine on Lake Rabun; very experienced with classics, but a wee bit far. Since you're on Lanier was hoping you might be able to recommend someone who's good with old inboards; i.e. Correct Craft and/or Century? (Also think it's time to repack the stuffing box on the Century.V-Drive so right under the tranny. Yuk. Would gladly pay someone I could trust) |
Posted By: MAN - GA
Date Posted: October-15-2011 at 3:23pm
| sorry don't have any recommendations I have just used this website for guidance and info and spent my time doing things |
Posted By: jimsport93
Date Posted: October-15-2011 at 4:55pm
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74Wind,
One of the site members, dmiracle, has an inboard mechanic that he uses on his 92 (I think) Ski Nautique. Never have used him myself, but dmiracle says he is very good. Don't know about his skills on older boats. Might be worth getting in touch with dmiracle through the site and see if you can get the mechanic's name and number. ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=2798 - 93 Sport Nautique |
Posted By: 74Wind
Date Posted: October-15-2011 at 11:49pm
| thanks anyway |
Posted By: 74Wind
Date Posted: October-15-2011 at 11:52pm
| thanks! |
Posted By: Jllogan
Date Posted: October-17-2011 at 12:43pm
You dont remember what the voltage was between the resistor and coil do you? Did you do a resistance test on the coil to check it? I am trying to find specs on what mine should be to make sure my coil is ok. Is there any auto store or shop that can test coils? ------------- http://correctcraftfan.com/diaries/details.asp?ID=5792&sort=&pagenum=1" rel="nofollow - 1986 Ski Nautique 2001 |
Posted By: MAN - GA
Date Posted: October-17-2011 at 1:18pm
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With your multi-meter setting on Ohms put leads on the + & - side of the coil it will tell you the primary resistance. Secondary resistance of the coil is between - post on coil and where the dist. lead plugs in. From my reading most points coils have a resistance of approximately 1.5 to 1.8ohms thus requiring about a 1.5ohm ballast resistor. The secondary resistance of the coil varies by manufacturer b/w 6k and 10k ohms, but this is subjective to the # of windings and total voltage.
Honestly I finally came to the conclusion that there is too much marketing on the coils and took the recommendation to just get the voltage to the points b/w 6v & 8volts max and don't worry about what the coil produces. I just needed to keep from burning the points, since I have done this I have not had any issues with my ignition. It took me two ballast resistors to regulate the voltage |
Posted By: Jllogan
Date Posted: October-17-2011 at 1:44pm
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awesome!! Thats what I was looking for your the man! ------------- http://correctcraftfan.com/diaries/details.asp?ID=5792&sort=&pagenum=1" rel="nofollow - 1986 Ski Nautique 2001 |