persistent misfiring - help!

Years ago I had a problem that sounds a lot like yours. Answer, new correct plugs.

Enjoy.
 
john charlton said:
I had the identical problem which baffled me . At last I changed the distributor cap and an instant cure . The car had been popping back through the carb as the wrong plug was being fired due to an internal short . The repro cap looked brand new . At some time I will do a post mortem on it to see what happened inside .

John in mild evening Suffolk County England .
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I've had that happen too. It took a while to find the problem and when I did. I replaced the body and while I was at it, I replaced the rotor button as well. Long story short, the rotor (brand new) was faulty. It was made with no lug on the inside to locate in the groove at the top of the cam. It moved so much that it ended up 1/2 way between contacts in the body so it sent spark to either at random. It sounded like WW3. Sometimes ya just can't win!:rolleyes:
 
OP states: "My A has suddenly developed severe misfiring as soon as it reaches operating temperature"

Does it matter if you open the GAV or feather the choke?

Can you isolate the miss to one cylinder? With engine warm, ground one plug at a time to evaluate how much that particular cylinder is contributing.

I'm wondering if you don't have a small vacuum leak? Easy enough to check by spraying WD-40 between block and intake juncture. If engine idle picks up, you've found the problem.
 
Check and make sure your gav is open and it could be a plugged cap jet inter carb.
Take it out and see if you can see through it and blow through it. Today's fuels can gum up quickly and block things up. Your backfire you describe may just be a lean condition popping.
Check it out and let us know
Larry Shepard
 
Giles said:
My A has suddenly developed severe misfiring as soon as it reaches operating temperature, with much backfiring of unburnt fuel through the exhaust and total loss of power. ...
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Am I correct in inferring that your car runs fine UNTIL it warms up? Is it driveable during that warmup interval? That's an important clue that eliminates a lot of possibilities, like plugged carb jets. However, due to thermal expansion, it does not eliminate as many of the bad-electrical-connection options as you might think.

For example, as far-fetched as it seems, the problem with the junction box screws shorting out to the firewall was reported to be worse after thermal expansion brought the metal pieces into closer contact--and also after passage of time had allowed the insulating coating of firewall paint to break down or be worn away.

Otherwise, boy! Your problem sure sounds like a bad condenser.

Steve
 
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Last month, our '31 A pick up was running ratty so I just replaced the Condenser with a new one. It ran an good for about twenty five miles and yesterday on a run, it started missing and loosing power again. I just barely made it back to my driveway. I traced the problem to the new condenser. The new condenser became bad too. I put another condenser in and it now runs great again. From now on, I had better carry a spare condenser with me. In an hour, I am going to town to buy some more extra condensers. Today's quality of condensers isn't what it used to be.
 
I was thinking the same as Steve in #26, and it's best to buy a good heat proof condenser and carry a spare. I've never had a coil, points, or condenser go bad on any of my cars, but have bought some bad condensers at swap meets.
 
pigtail wire in the distributor and/or condenser are often culprits in a car that has been performing well before going bad.
You checked the compression but sometimes an exhaust valve may be sticking open allowing fuel to enter the muffler.
 
If you are at your wits end run the car in darkness which may show you a short circuit. A number of years ago my car ran poorly and I did not find the problem until I checked it in darkness and found the problem right away.
 
A good test to diagnose such problems: Remove the carb drain plug & with a container, see if you have a constant fuel flow, for at least a MINUTE or so!
Bill W.
 
Wow, thanks Markus! Excellent write-up on your web page. Very well documented. Thanks again. Jeff
 
JDupuis said:
Wow, thanks Markus! Excellent write-up on your web page. Very well documented. Thanks again. Jeff
Click to expand...
JD,
I've been following Markus' restoration for YEARS! He's an AMAZING, GENIUS Man!
If you want to learn some AMAZING facts & info, just read the WHOLE thing!!!
Bill Williamson
 
Here is something I ran into that would cause your problem. The point arm spring broke, but there was still a little tension keeping the points closed. As soon as you revved it, the points would float. Just feel the spring load on the point arm to make sure it it has some guts.
 
The symptoms sound like they could be caused by a manifold leak, but why do they only appear after warmup?
 
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