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EFV-8 Club Forum / 1940 Ford Discussion / Carburetor

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Discussion Topic: Carburetor

misfit

08-02-2017 @ 12:22 PM

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Posts: 10
Joined: Dec 2011

Why does my Ford carburetor in mid throttle (not idle)
stumble jerk or lurch when accelerating and or holding throttle at specific speed. Holding the throttle to the floor it does it also.
Two years ago the car ran fine. I rebuilt the engine went 80 over. Then the stumbling started. I changed the jets to 46 from 48 it seemed to quit doing it. Two years later the carb for some reason wants to leak fuel all the time. I put on a new Mac's Carb at the problem returned.
I have a holly pressure regulator set at 3-1/2 lbs. a 6 volt fuel pump. running thru the mechanical fuel pump (the valves are removed in fuel pump).
I live in Colo 6700 feet, I drove to a lower alt and the car drove great came back home and it started giving me trouble again. I used #50 & 48 jets. Len

This message was edited by misfit on 8-2-17 @ 12:24 PM

carcrazy

08-02-2017 @ 1:03 PM

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An old rule of thumb for getting a car to run properly at altitude (5,000 ft. above sea level ie. Denver) is to go down two main metering jet sizes and to go up four degrees in initial spark advance. The carburetor likes to see 2 1/2 PSI of fuel pressure at sea level.

42oink

08-07-2017 @ 9:58 AM

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Greetings, Is that gauge reading 5+ lbs? Hmmm.. I, too, have a similar stumbling problem with a 42 Ford, stock fuel pump , and have tried changing power valve in carburetor, changed distributor numerous times checking point gap and degrees open and closed, and timing. All with no perceivable difference. I therefore wait with baited breath for more of the experts to offer ideas. I wish us both luck. 42oink

misfit

12-29-2017 @ 4:07 PM

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My stumbling issue has been resolved. I have #48 jets because I'm at 6800 ft. I did have #50 's in but you couldn't stand behind the car without gasping for air. I was using a power valve with the springs cut to allow it to not open until a higher vacuum. It seems that modification was causing the carb to run lean. I put back the original power valve. It seemed to correct the problem. However this is with the new carb. As for the vacuum advance it's in the middle of the scope of adjustment. Timing is at 4deg. I hope this helps. Misfit

TomO

12-30-2017 @ 8:54 AM

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The power valve stays closed until the vacuum drops below it operating settings. Clipping the spring gave you an unknown opening value. The 5.5 power valve should work fine for you. If you are having rich mixture problems, with the 5.5 valve, it is probably caused by a leaking power valve or body to base gasket.

Your car will probably run better in the higher altitudes with the 11A advance mechanism. If you still have the 68 advance mechanism, you can advance the initial timing by up to 6 degrees by moving the bolt on the side of the distributor down. Each mark is 2 degrees advance.

Tom

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