Guys, I need some expert flathead advise from someone who know them well. I have 59A in '30 Model A coupe and it is old and tired but has been a great runner. I love driving the old girl so I don't want to tear it apart yet because with my lack of time and family commitments it would sit in pieces for along time. The 59A is bone stock with a single Holley 94 that has been rebuilt many times and the diving bell style distributor. So for about two years it has started having this issue where it stumbles and falls on its face, popping in the exhaust in the higher RPMs like just about when you shift into the next gear. It only does it under load, you can rev it up in neutral and it is fine. Initially I thought is was condensation ( water in fuel) in the tank so I drained in and put fresh gas in, still the problem persisted. I thought it was ignition related but I checked the points and they were fine, replaced the rotors and replaced the plugs, still the stumble was there. Then I was reading about ethanol and what is does to carbs so I rebuilt the carb for a second time and the problem went away for about 3 months and then it returned leading to believe that is was carb related. So this weekend I cleaned up the carb and rebuilt it again, used carb cleaner and blew all the p***ages out and rebuilt it with a kit from speedway. I drove it yesterday and it is just the same as before in the high RPMs, stumbles, falls on its face, picks up and clears out, pops through the exhaust, basically undrivable now. My feeling is I need to order a new 97 for the car and be done with it but I don't want to drop $250 if there is chance it is ignition related. Any flathead gurus want to give there opinion?
I'm just a shady tree mechanic, but have you done a compression test on it lately? You can throw all the new parts you want at it, without good compression you're wasting your efforts and money.
Could be carb or ignition either one, wouldn't hurt to just go step by step though a tune up with it. I had a two cylinder motor that was stumbling the other day and found a tight exhaust valve. that helped it some I still have to chase an ignition gremlin but loosening up the valve lash helped it. Tight vale lash is the nemesis of tall revs.
Not a flathead guru here either, but I'd be looking at the fuel supply first. Pump, pressure. filters, etc. Since it did run good at one time, I'd be checking a lot of things before I bought a new carburetor, Good Luck!
You can usually see a carb problem, however, lack of fuel to it or lack of ignition can cause under load problems. Will ignition jump a wide gap?
Two quickies that MIGHT show you where to look: First, drive the car through its stumble point repeatedly while pulling the choke out more on each run. If you hit a point where it gets better, look at carb. Remember with 10% ethanol you are a point or two lean, which might have aggravted a marginal setup. Second, find the little scale on side of distributor and advance it several lines. Repeat testing...of course you don't want to do an extended high speed drive while it is advanced! Actually, before that test even, loosen the vac brake. Screw it out BY HAND until you feel the end of adjustment, go back 2 turns or a bit less. If this is much tighter than that, it is slowing your advance too much for modern gas.
It did clear up when I rebuilt the 94 last time but I am not sure why it did not help this time? Popping througnt the exhaust is usually a lean issue from my experience ( starving for gas). It has an electric pump that feed 3psi and has worked great for years so I don't think it is delivery problem unless the accelerator pump is not working properly, I replaced it with one from the rebuild kit and no change.
The accelerator pump is only in play as you are pushing down on the pedal, a squirt. What you describe sounds like the bowl is running dry after a few seconds of higher speed running. Are you sure about the float level? Filter?
The choker diagnostics is a good trick! But other then than there rule of thumb is; If you played work something and it got worse, you did son thing wrong. If you did something and it did no difference. if you played with something and it got better you should be proud! Do a fast leak down test. And then I would go backwards in the fuel system. Till the tank. Pull plugs and check everything! And right way back is; filter, pump, pipes, tank and cap. Just a quick over on everything. And remember there can be a filter in carb inlet, inline in fuel hose, pump in where a fuel hose is connected to the fuel pipe, just out side tank and just in side tank. Flush all pipes or blow them out, and when in doubt, pull all hoses. Ignition go true the cables/plugs, cap/roter (no excessive play), condenser, advance (starting point and curve. Swing blocks and vacuum). Most everything else in ignition is on/off or go/no go. This is all from personal experience, you experience might be different.
Sounds like fuel pressure. Might try jacking up the pressure to 5 / 6 #'s for a test. I run my 48's @ 5 #'s regardless. Grosse jets...
Sounds like the timing is a bit late. Try advancing the timing a little. Also check the condensor its possible its going bad.
I checked the pump and it is delivering 5psi and plenty of volume so I don't think I fuel delivery issue. I did pull the coil off and it is worn and appears to be an OG 6 volt Ford part that has had 12 volts running to it with no balast resistor, so when the RPM come up under load I need a hotter spark but the weak coil cannot provide it so it stumbles and pops through the exhaust?? I will check the coil for resistance and then see about having it rebuilt 12 volt like it should be.
Alot of good suggestions above. Had one drive me nuts for a year. Pointed to everything but electrical. Changed the damn condenser and it was a miracle.
I checked the resistance on the coil and it was really weak so I think that is my problem when the demand increases the coil cannot keep up, I am sending it to skip Haney to have it rebuilt and I will install a new condenser as well. I think that will fix my stumble, thanks for all the advice.
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