Engine will not reach max RPM
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=43334
Printed Date: October-06-2024 at 12:21pm
Topic: Engine will not reach max RPM
Posted By: starbox189
Subject: Engine will not reach max RPM
Date Posted: August-05-2018 at 9:38pm
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Hello All: I have a 1981 Southwind with a PCM Ford 351. I recently had water in the engine oil and had new head gaskets installed, heads planed, new exhaust manifolds, new plugs plus other misc new parts. The oil was changed 5 times to clear out the water. The oil looks perfect now. The engine used to max out at around 4400 RPMS. Now it only gets to 3600 RPMs. Timing is 10-11 degrees BTDC at idle, timing, advance is okay, dwell is okay. It sounds great and runs smoothly but won't go past 3600. It has around 450 hrs. The marine mechanic who did the work is a very experienced and I have known him for years. He can't figure it out. Any thoughts?? |
Replies:
Posted By: 8122pbrainard
Date Posted: August-05-2018 at 10:22pm
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Sounds like the water got in from the top end??? What readings did your mechanic get from a compression test after the repair? ------------- /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: starbox189
Date Posted: August-06-2018 at 2:55pm
| What should the compression be? Thanks. |
Posted By: 8122pbrainard
Date Posted: August-06-2018 at 4:10pm
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The actual reading is not as important as the variance between cylinders. All cylinders should be within 5% for best performance or a max of 10%. Depending on performance level, stock engines run 130 to 200 psi new. Didn't your mechanic run a compression test? ------------- /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: 63 Skier
Date Posted: August-06-2018 at 6:47pm
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So, same boat, prop, etc. and lost 800 rpm. My first comment would have been to check advance and total timing, sounds like you did that, when you say advance is OK you had a timing light that could read total timing? If not timing then fuel, might want to get a pressure gauge on the fuel delivery to make sure the pump is putting out enough pressure post rebuild. Also look to see if secondaries are opening fully. ------------- '63 American Skier - '98 Sport Nautique |
Posted By: MACS81SN
Date Posted: August-06-2018 at 7:14pm
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Verify secondaries on carb opening properly. 34-3600 is about where they start opening ------------- Mark 1999 -SN - 502 Python 1981 - SN Owned 33 years - Sold 1968 - Mustang - Sold |
Posted By: Bri892001
Date Posted: August-06-2018 at 8:27pm
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Agree with Mark. Was also thinking to check that the throttle cable is allowing the carb to open up to full throttle. A lot of stuff on your top end was taken apart and put together. Throttle cable is an easy thing to pinch or potentially to connect wrong. |
Posted By: starbox189
Date Posted: August-07-2018 at 9:04am
| Mechanic said he checked compression and it was consistent at 110 psi. Wondering if he just assured me he did to appease me. Anyway, I think I'll check the carburator secondaries, fuel filter and fuel pump next. |
Posted By: 63 Skier
Date Posted: August-07-2018 at 10:01am
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I can see getting 110 since the engine wasn't rebuilt, but would not expect 110 across the board, more of a range than that. Just guessing but seems unlikely it would be that consistent. How many hours are on the engine? Anyway, I don't think compression is your problem so go ahead with the other suggestions. ------------- '63 American Skier - '98 Sport Nautique |
Posted By: samudj01
Date Posted: August-07-2018 at 12:25pm
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Sounds similar to our issue last summer.. I was convinced it was carb related...ended up being the distributor advance. Make sure the plates move freely and that the springs are still good. And of course, also check that the secondaries are opening. You may want to take a look at our thread "New to me 78 Tique" ------------- 78 Ski Tique, 72 Skier w/302's, 93 SN w/351 & 17 GS22 w/zr409 Previous - 99 Sport Nautique w/GT40 and 87 Martinique w/351 |
Posted By: 8122pbrainard
Date Posted: August-07-2018 at 4:25pm
What is the advance your mechanic found or did he just tell you it was "OK"?? ------------- /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 < |
samudj01 wrote: