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Discussion Topic:
52 Merc. Holley
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mikemerc |
04-15-2020 @ 8:47 AM
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Member
Posts: 23
Joined: Jul 2019
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Hey guys ,back again. With all the things I’ve checked I’m thinking the carburetor might be my problem. Maybe a clogged fuel passage or I’ve heard it may be a power valve? Any ideas on where to get a rebuild kit ? I probably should have mentioned this before, this problem happens when engine is hot or cold,it will rev right up but breaks up when you try to hold the rpms steady. Thanks for any and all help mike.
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ford38v8 |
04-15-2020 @ 9:55 AM
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Senior
Posts: 2734
Joined: Oct 2009
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Mike, What hasn't been addressed by anyone so far is the flex line from firewall to pump. They tend to collapse internally, causing a restriction that impedes flow, sometimes just enough to cause a miss like yours. Bob Shewman has fuel resistant flex lines: 610-993-6637
Alan
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mikemerc |
04-15-2020 @ 1:00 PM
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Member
Posts: 23
Joined: Jul 2019
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Alan, I did replace that hose before checking the fuel pump pressure and volume.thank you for your input. Mike
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TomO |
04-16-2020 @ 7:47 PM
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Senior
Posts: 7243
Joined: Oct 2009
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Daytona parts has a kit for your carburetor. That is not an easy carb to rebuild. Be very careful to tighten the screws just enough to close the lock washer and alternate sides when doing this. You do not want to warp the dicast. Set your choke to the rich side and see if that helps. If it does, you have a fuel delivery problem. Watch for fuel dripping from the upper chamber, if you see some the carb needs rebuilding or replacement. Check your dwell at all speeds it should not vary more than 1 degree. If it does, the bushings in the distributor will have to be replaced. Do a cylinder balance test at about 15oo rpm. Short out each plug and watch for a rpm drop. All cylinders should give the same rpm drop. If one or more cylinders have a smaller drop, check the plugs and compression. Dribble some MMO down the carb, you may have sticky valves. Vacuum gauge readings would also help diagnose the problem.
Tom
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mikemerc |
04-17-2020 @ 6:28 AM
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Member
Posts: 23
Joined: Jul 2019
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TomO , Thanks for the info . Guess I’ll start with the easiest.gettting some mystery oil today. Thanks mike
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Barney |
04-17-2020 @ 7:44 AM
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New Member
Posts: 107
Joined: Nov 2015
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Hi Mike, Here's my 2-cents' worth (maybe only a penny's worth). Let's assume the stumbling starts to rear it's ugly head at 2500 RPM. I certainly don't disagree that it appears to be a fuel starvation issue, or an ignition issue. But I would ask: Does this issue occur during a no-load condition the same as it does during a heavy-load condition? Obviously, significantly more fuel is required to maintain 2500 RPM at heavy-load vs. no-load. If the engine starts to stumble at 2500 under either of the aforementioned conditions I'd say it's safe to declare fuel is not the issue. Of course, it could still be an ignition issue. And I know you don't want to hear this, and I hope I'm wrong, but have you thought that you may have a couple, or a few, weak valve springs? Good luck. Barney PS Has your machine been tested for the C-19 virus?
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mikemerc |
04-17-2020 @ 10:15 AM
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Member
Posts: 23
Joined: Jul 2019
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O.K. Turns out that I hadn’t looked down the throats of the carb deep enough to see that a good amount of gas was dribbling down into the engine with the throttle at 1/4 open .More throttle Above 1/4 the worse it ran. I’m looking into a rebuild kit from Daytona parts. Thanks to all you guys who helped out .Thanks to TomO Who gave me the idea to check a little harder for the drips down into the carb. Feel like a dope for not doing it a while ago. Does the rebuild require special tools or can you get away with regular tools .the manual makes it look pretty intense. Thanks to all ,hope I can return the favor one day. Mike
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mikemerc |
04-17-2020 @ 11:15 AM
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Member
Posts: 23
Joined: Jul 2019
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Barney, It doesn’t affect any different from being in park at high revs or out on the road at 40-60 mph. It has been mentioned about weak valve springs ,but a buddy did a few checks with a vacuum gauge and didn’t see anything during his test. I think I found the problem,it’s in the carb . Too much gas. Gas is dripping gas down into the throats when throttle above an idle and on up. And yes , I tried to get it tested for the virus but they couldn’t get those Q tips past the air breather!
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mikemerc |
04-17-2020 @ 11:31 AM
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Member
Posts: 23
Joined: Jul 2019
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Any ideas on why gas would drip down from upper bowl or possibly out of the nozzle tubes that are connected to throttle plates. It looks more like out of those tubes than up above. It appears that it doesn’t drip at an idle,and it runs really good at idle.
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carcrazy |
04-17-2020 @ 1:52 PM
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Senior
Posts: 1582
Joined: Oct 2009
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Fuel is supposed to flow into the air stream as it passes through the venturi region of a carburetor. This is the basic principle upon which all carburetion systems work. With carburetors that have a fixed venturi there are several systems that work together to provide the correct amount of fuel for each operating condition. The idle system provides the correct air/fuel (A/F) ratio for idle speed. The transition system provides the correct A/F ratio for speeds between idle and about 1,500 RPM when the main system takes over and fuel begins to flow through the venturis. It is normal for you to see fuel flowing from the venturis once the engine speed gets to 1,500 RPM or so. To solve your problem, look into the ignition system. An old rule of thumb when diagnosing engine running problems on a spark ignition engine is that 10% of the time its a fuel problem and 90% of the time it is an ignition problem. I suspect that you have something causing weak spark at the higher engine speeds. The dwell may be incorrect at the speed where the problem occurs or the contact breaker points spring tension may not be sufficient allowing point bounce or other problems.
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