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Old 07-02-2015, 08:19 PM   #1
Jeff/Illinois
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Default # 4 cylinder misfire

Didn't have time to stay in the garage tonite, have to be gone next few days but was digging into 'why' the Roadster was running under powered and missing.

Cleaned out sediment bowl, blew out fuel line, and took carb apart and blew it out not a speck of dirt. Gasoline is fresh. Strong fuel flow.

Started playing with the ignition side, checked timing, point gap, all fine. Took out plugs from front to back, numbers 1-2-3 looked good all gapped at .035 took out # 4 plug and it was wet from gasoline, not firing apparently. These are Champion plugs I put in last fall, going to put back the set of Motorcraft TT10's I took out and try for a spark test to track down the why. Have backup dist. body, rotor, and cap

When I can get back to it I'll re-post what I find. Out of time right now.

Forgot to add,,,, left out #1-2-3 plugs and cranked engine by hand, and had fairly good compression on #4 w/ that plug in. Seemed normal anyway.

Last edited by Jeff/Illinois; 07-03-2015 at 08:32 AM.
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Old 07-02-2015, 08:52 PM   #2
jax55
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Default Re: # 4 cylinder misfire

Could just be a bad spark plug. Try moving #4 plug to another hole and see if the problem follows.
I had the same problem once, and it was caused by the point gap closing due to the rubbing block wearing. Don't ask we why number 4 in particular... that is just what happened.
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Old 07-03-2015, 03:47 AM   #3
Mitch//pa
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Default Re: # 4 cylinder misfire

The FIRST thing I do for a miss is short each plug out to determine which cylinder is at fault, and at the same time you can see if that offending cylinder is getting a good spark."""" i then know where to attack"""""""...since you already checked compression etc try spraying or inducing propane around the offending intake runner on the cylinder not firing for an intake gasket leak. just another quick check or do the plug swap you already mentioned.
good luck i hope its something simple

Last edited by Mitch//pa; 07-04-2015 at 03:34 PM.
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Old 07-03-2015, 06:17 AM   #4
Tom Wesenberg
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Default Re: # 4 cylinder misfire

Twice I've seen distributor bodies short between 3 and 4 and cause a misfire.

Last weekend I helped a friend get his old Honda 90 three wheeler running right. It would start and idle, but quit after running a couple minutes. Normally this would sound like a lack of fuel problem, but in this case it turned out to be a fouled plug problem. Normally a fouled plug clears up after getting hot, but this is the first time I saw a fouled plug get worse as it warmed up. Anyway, a new plug had the Honda running perfectly again.
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Old 07-04-2015, 03:28 PM   #5
Jeff/Illinois
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Default Re: # 4 cylinder misfire

Back in town now,,,, followed Mitch's advice and sure enough, it WAS firing to the plug on #4 but the spark plug wasn't doing it's thing.

I laid the plug on top of the block, turned on the ignition, cranked the engine by hand and 'no spark'. Swapped out a different plug and there was spark then.

I've never had that in all the time I've been fooling with Model A's or any other car for that matter. Tossed the Champions in the garbage and went back to the Motorcraft TT10's. A bit cooler plug than I'd like but at least they work!

Thanks Mitch and Tom,,,, and everyone have a happy 4th of July! Saw a nice '30 Roadster Pickup in another town's parade, was a 'lighted parade' too dark to get a picture. Beautiful truck!

Forgot to add, the Champions were from about 30 years ago been running them for maybe a year. I think they were 16-C's(??) forgot now just what they were.
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Old 07-04-2015, 05:20 PM   #6
Patrick L.
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Default Re: # 4 cylinder misfire

They can go bad just like anything else, stuff happens. If one is dropped or even tapped by mistake a failure can happen.
I tend to prefer Autolites or Motorcraft, but, Champs are good sparklers.
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