My 390 backfires when cold
New User
Joined: Jan 2000
Posts: 7
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My 390 backfires when cold
In the morning I'm backfiring; also when I stop after a long trip. I was told to adjust the choke. Any advice?
I have done a lot of work to the truck including rebuilding the engine. I have a new carb and new points and distrib cap/rotor/plugs/wires. I might have missgapped the points on accident. My exhaust pipe and manifolds were both leaking after reinstalling them. The pistons are loud. Any problems from exhaust leaks?
I have done a lot of work to the truck including rebuilding the engine. I have a new carb and new points and distrib cap/rotor/plugs/wires. I might have missgapped the points on accident. My exhaust pipe and manifolds were both leaking after reinstalling them. The pistons are loud. Any problems from exhaust leaks?
Elder User
Joined: Jun 1999
Posts: 861
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From: SE PA
My 390 backfires when cold
A couple of things may cause this, the exhaust would be the first thing to take care of, if it's only leakin' on a couple of cylinders this will make it very hard to tune as some are runnin' with backpressure and some would not, causin' a lean condition in the leakers. Also when colder air is introduced into the exhaust system, if there is any unburned fuel in the exhaust, the "extra" air will induce a backfire as it burns the unspent fuel (when it's cold and chokes on it's a little rich). Of course points bein' off could also cause this as could the choke, but seein' how it does it when it's warmed up, I would not consider these things until the exhaust is repaired. Also, make sure you don't have any vacuum leaks, this could also cause the problem you have and would be most noticable when cold. Hope this helps, Chuck P.
Senior User
Joined: Jan 2000
Posts: 103
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My 390 backfires when cold
I would suggest that you re-check your timing, make sure you have good clean gas, if you are in freezing temps at night water might condense in you gas tank if you do not keep it full, try adding some "heet" or a product like that. Another thing to check is to make sure you have all the plug wires routed right. They have a tendancy to crossfire if they are not in the proper position or if you are using your old plug wires make sure they are not crossed especially when they are wet and frosty. Hope some of this helps..Good luck
2x2
2x2
New User
Joined: Jan 2000
Posts: 7
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My 390 backfires when cold
Thanks.
I live in CALIF so it wont freeze much. I forgot to mention, the truck dies when it is first cold started. If I raise the idle, it will be very loud at stops. So I think I will fix the exhaust first.
The exhaust leaks at the p.o.c. of block/manifolds/pipe. I didn't use silicone when reinstalling them. One of the bolts is stripped on the pipe end. Since I will need to replace the manifolds and pipe eventually, can I just quick fix the pipe/manifold connection? I though of J.B. weld or a similar metal compound. Is there an exhaust wrap or something to perminately seal the connection?
I live in CALIF so it wont freeze much. I forgot to mention, the truck dies when it is first cold started. If I raise the idle, it will be very loud at stops. So I think I will fix the exhaust first.
The exhaust leaks at the p.o.c. of block/manifolds/pipe. I didn't use silicone when reinstalling them. One of the bolts is stripped on the pipe end. Since I will need to replace the manifolds and pipe eventually, can I just quick fix the pipe/manifold connection? I though of J.B. weld or a similar metal compound. Is there an exhaust wrap or something to perminately seal the connection?
