Fuel system issues - help please
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=42091
Printed Date: May-08-2024 at 3:53am
Topic: Fuel system issues - help please
Posted By: 79ntique
Subject: Fuel system issues - help please
Date Posted: October-29-2017 at 12:31am
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After having my 79 Nautique carb rebuilt, I have not been able to keep it running below 1500 rpm's ? After re-installing the carb, it ran great for about an hour, but will now only run at 1/4 throttle and up. I think I've checked all of the basics (new fuel filter, cleaned anti-siphon valve, new fuel pump). It would seem that something happened with the carb rebuild, but I pulled the carb and it ran good on a dyno-engine at the carb shop. Can anyone offer troubleshooting advice ? Thanks '79 Nautique, 351 Commander, 4 barrel, Holley D4JL -- 9510, elec choke, New fuel filer cartridge, new fuel pump (7-9 psi). |
Replies:
Posted By: KENO
Date Posted: October-29-2017 at 12:44am
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Sounds like a vacuum leak. Did you replace the gasket between the spacer and the manifold along with the one between the carburetor and the spacer.? Some gaskets don't fit real well between the spacer and manifold leading to a vacuum leak and the symptoms you have. |
Posted By: Duane in Indy
Date Posted: October-29-2017 at 8:30am
Sound like a candidate for the old ether, or propane leak check. Only us old guys know that trick. Right Pete, and KEN???  ------------- Keep it as original as YOU want it 1978 Mustang (modified) |
Posted By: 8122pbrainard
Date Posted: October-29-2017 at 8:42am
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Duane, I prefer the propane trick as is less volatile!  ------------- /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: 8122pbrainard
Date Posted: October-29-2017 at 8:50am
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It's easy: https://www.hunker.com/13414896/how-to-find-a-vacuum-leak-with-propane" rel="nofollow - How to check for vacuum leak using a propane torch ------------- /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: Gary S
Date Posted: October-29-2017 at 10:05am
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I went through this about a year ago when I put a 4bbl on the Shamrock. If a Commander is the same as a PCM there isn't a aftermarket gasket that will fit a stock iron manifold and the pcv adapter. They are not off by much but enough to cause trouble. You need to use a genuine PCM gasket. If I have them here I will post a picture later, I have extras since they are hard to get. I'm not pulling a Ken and taking it apart. ------------- 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: KENO
Date Posted: October-29-2017 at 10:26am
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Here's a picture from the past of the bottom of a PCM spacer. Not a lot of sealing area there and like Gary said it's a tough thing to seal with aftermarket gaskets. Fairly easy to make your own from a piece of gasket material from most any parts store or buy the PCM gasket. Just need to make it bigger around the outside edges Put the spacer on the gasket material and trace around the outside and then cut it about 1/4 inch bigger on the edges Inside can be the original size 
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Posted By: 79ntique
Date Posted: October-29-2017 at 11:45pm
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Thanks guys-- the leaking gasket makes complete sense; I'll test it out in a few days, but I think you are spot on with the fix. I installed a new base gasket, but it was an aftermarket, looked close, but must have failed after an hour of running... I really appreciate your help; after 20 years of tinkering with this thing, I think I know it, but I often prove myself wrong -- thanks again.. 
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