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Old 04-14-2020, 06:59 PM   #1
russcc
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Default Misfireing at idle.

So now she's starting & running, but misfiring at idle, 1 or 2 cylinders off & on. Since winter here was warmer than usual, but with big swings in temperature, and a lot of rain, no snow, there was condensation on the heads and headers from time to time as the temperature swung back & forth.
Valve hanging up ?, cure ? Thank you Fordbarners
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Old 04-14-2020, 07:56 PM   #2
cmbrucew
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Default Re: Misfireing at idle.

Moisture inside distributor caps.
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Old 04-15-2020, 06:49 AM   #3
russcc
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Default Re: Misfireing at idle.

Thank you for the that thought. During no start trouble shooting and before the 1st start, I pulled the cap, 21A, and checked inside. Clean, dry, no visible carbon tracks. Cleaned it inside any way with electronic cleaner & wiped it out. Backfires ?
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Old 04-15-2020, 07:19 AM   #4
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Default Re: Misfireing at idle.

I have had that happen with bad plug wire.

When you say backfires, out the tail pipe or the carburetor?
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Old 04-15-2020, 07:22 AM   #5
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Default Re: Misfireing at idle.

Definitely ign. problem, either weak springs or worn dist. shaft and bushings. And at higher rpm, centrifugal force keeps shaft from wobbling. That's just my guess!
If it was a stick valve it would miss at all rpm.
Good luck!
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Old 04-15-2020, 08:15 AM   #6
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Default Re: Misfireing at idle.

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condensor condensor condensor ............
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Old 04-15-2020, 06:49 PM   #7
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Default Re: Misfireing at idle.

The quickest way to test for a cracked dist. cap is to fog the inside of the cap with WD-40. If the roughness goes away, replace the cap. Otherwise, do as Bubba says and replace the condenser........Bob L
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Old 04-15-2020, 11:19 PM   #8
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Default Re: Misfireing at idle.

as said condenser. You can find out if there is a sticky valve at idle with a vacuum gauge. I have a full time vacuum in the 36 cab also to test load vacuum. If so you know the treatment. MMO dump on the carb and run it then repeat. If you have an aversion to MMO (not sure why) a little diesel fuel might work too, maybe. I don't want to to be one sided (mmo will work and do no harm). Could be anything really.

Last edited by Tinker; 04-17-2020 at 09:24 PM. Reason: spelling aversion. No big whoop, just thought I'd change it.
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Old 04-15-2020, 11:57 PM   #9
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Default Re: Misfireing at idle.

L head motors relied on fuel with lead to lubricate the valves. No lead, is a good thing. But there is little oil to the guides also. Just a thought.
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Old 04-16-2020, 02:57 AM   #10
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Default Re: Misfireing at idle.

Two plug wires crossed?
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Old 04-16-2020, 03:12 AM   #11
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Default Re: Misfireing at idle.

Quote:
Originally Posted by BUBBAS IGNITION View Post
condensor condensor condensor ............
Agree Agree Agree - A word of warning the last two I have used new out of the box have been faulty -Karl
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Old 04-16-2020, 06:32 AM   #12
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Default Re: Misfireing at idle.

do a compression test, eliminate the easiest first
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Old 04-16-2020, 08:43 AM   #13
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Default Re: Misfireing at idle.

aside from condensers I think it could be some carbon crap on valve seats. All it takes is
a dot like fly crap. solution drive it. All I reed here in my mind is people putting cars to sleep all winter and expect it to run next year in summer. My car all year sleeps out
side, on the coldest days 2 pumps hit button and, its a running with no choke. Like I have a neighbor with the most mint 30 Ford 41 Chev and 38 Plymouth: All only come out to
get inspection sticker-once a year: I think about him, no kids 80yrs old then his time comes I hope all you know what this means; Ao, attorneys r scrap yard.? Thats why I drive my car and my 23T & then drop dead , not my problem no more... Life is too shot
enjoy the thing....drive it like ya stole it
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Old 04-16-2020, 11:59 AM   #14
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Default Re: Misfireing at idle.

It could be a lot of things. How old is the gas? I'm with Oldbugger,test instead of guessing.
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Old 04-16-2020, 12:15 PM   #15
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Default Re: Misfireing at idle.

What 'oldbugger' said in #12 above. I'm leaning toward a valve sticking/hanging up....
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Old 04-17-2020, 01:22 PM   #16
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Default Re: Misfireing at idle.

Don't forget to check the points/gap.
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Old 04-17-2020, 07:38 PM   #17
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Default Re: Misfireing at idle.

Waiting till it warms up again in the barn. Will check the plugs wires 1st, make sure they are in order. Next do a vacuum test. Then, take the condenser to my friend Ray who has a tester. Are those Vertex condenser still made in Arizona anyone know. I know they are expense, but worth it.
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Old 04-17-2020, 09:15 PM   #18
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Default Re: Misfireing at idle.

When testing the condenser, make sure you heat cycle it.
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Old 04-18-2020, 06:08 AM   #19
russcc
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Default Re: Misfireing at idle.

That's how the tester works.
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Old 04-18-2020, 10:58 PM   #20
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Default Re: Misfireing at idle.

We had problems recently with very rough idle.Turned out there was a tiny hole corroded between one of the cast iron intake manifold throats and the exhaust heat riser. Quite hard to find but another manifold fixed it.Cheers.
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