Occasional miss
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Posting Guru
Joined: Jan 2013
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From: Wichita, Kansas
Occasional miss
Hey guys i have a puzzler on my 390. She occasionally misses at idle in park. In gear it isn't noticible. I did the math and at idle the engine is rotating around 11 times a second. It only hits maybe 20-50 seconds apart from each other. So it fires fine for a while, a random misfire, then its okay again
Laughing Gas
Joined: Jul 1999
Posts: 1,047
Likes: 22
From: Lacey, WA
What are the conditions of the plugs and wires? New, old?
Does it do this when only cold start up or only hot start or?
If when hot only I would consider that the coil is breaking down.
Good Luck,
Lee
Does it do this when only cold start up or only hot start or?
If when hot only I would consider that the coil is breaking down.
Good Luck,
Lee
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Posting Guru
Joined: Jan 2013
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From: Wichita, Kansas
Plugs and wires are brand new. Accel 8mm, accel super coil, and autolite double plat spark plugs. It becomes more frequent in the winter and when its cold. When warmed up it stops.
Laughing Gas
Joined: Jul 1999
Posts: 1,047
Likes: 22
From: Lacey, WA
Grasping at more straws here.
I see you are in Kansas. How cold is it when you have the trouble? I ask because I wonder if the Carb is icing up.
Are you running the stock air cleaner with the heat riser tube or ?
I see you are in Kansas. How cold is it when you have the trouble? I ask because I wonder if the Carb is icing up.
Are you running the stock air cleaner with the heat riser tube or ?
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Posting Guru
Joined: Jan 2013
Posts: 1,550
Likes: 0
From: Wichita, Kansas
It is the same in the summer and winter until she gets warmer or in drive. I have an open element air cleaner on
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FTE Leadership Emeritus
Joined: Jul 2002
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From: Long Island USA
Is it points? Because everything else seems to have been checked or is new...
Check the top bushing in the distributor. If it's loose, it can cause all sorts of whacky things. Even if it's an electronic distributor, the gap between the pickup and the wheel, if it changes at all, can cause weird things.
Also, since you say it stops when it warms up fully, it's possibly the choke is TOO much, it's running every so slightly rich, and causing the misfire. When you put it in drive, it causes a load, so it needs the rich mix. Put it back in Park, no load, doesn't require as rich a mix, begins to randomly misfire again.
Check the top bushing in the distributor. If it's loose, it can cause all sorts of whacky things. Even if it's an electronic distributor, the gap between the pickup and the wheel, if it changes at all, can cause weird things.
Also, since you say it stops when it warms up fully, it's possibly the choke is TOO much, it's running every so slightly rich, and causing the misfire. When you put it in drive, it causes a load, so it needs the rich mix. Put it back in Park, no load, doesn't require as rich a mix, begins to randomly misfire again.
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