390 Backfires
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Laughing Gas
Joined: Jul 2010
Posts: 1,127
Likes: 122
From: Chico, Ca.
390 Backfires
Ok here we go. I have a '65 F250 with a 390, 2bbl, auto, with a stumble at takeoff and will backfire while driving, which seems to get worse as the engine heats up. I have replaced the dizzy with a stock rebuilt and reinstalled the pertronix III. My total advance is 38 deg. with an intial of 12 deg. I have also rebuilt the carb twice (autolite 2100) taking special care to completely clean the body and blow out all the passages. I have replaced the rubber fuel lines and installed a new mech. fuel pump. What stumps me is that the engine revs nicely in park, but starts to miss when put in gear. The transmission shifts fine. What am I missing?
Kurt
Kurt
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Laughing Gas
Joined: Jul 2010
Posts: 1,127
Likes: 122
From: Chico, Ca.
Thanks Allen. No sucking, just blowing. There seems to be good flow coming out of the pipes. I'm going to replace the hose to the trans and see if that helps.
Kurt
Kurt
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Laughing Gas
Joined: Jul 2010
Posts: 1,127
Likes: 122
From: Chico, Ca.
Thanks. The intake leaks a little oil at the back, so I suppose it could be the culprit. I have been dreading that particular job, since the intake I have is cast iron.
Lead Driver
Joined: Oct 2004
Posts: 8,062
Likes: 35
From: Central Oregon
The oil leak in the back is fairly normal on a FE engine and I hear you about the cast iron, I have two FE's that I have to pull the intakes over the winter because of the leaks in the back. But a leak in the back does no mean it is leaking vacum.
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Laughing Gas
Joined: Jul 2010
Posts: 1,127
Likes: 122
From: Chico, Ca.
Update
I have done a number of things to the engine, since the initial post. Replaced timing chain with double roller. New glasspacks (blew out old muffler because of bad timing chain). Replaced old 2bbl intake with Performer RPM and Performer 600 cfm carb. Blocked off exhaust crossovers at head. Used right stuff to set intake manifold. No oil or vacuum leaks that I can find. Set timing @ 12 deg with total advance around 38 deg. Truck ran great initially, then started missing and stumbling while driving. Finally got around to a compression test. #1 - 135, #2 - 130, #3 - 125, #4 - 138, #5 - 128, #6 - 140, #7 - 130, #8 - 130. Any suggestions before I start tearing things apart again? Thanks.
Kurt
Kurt
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Laughing Gas
Joined: Jul 2010
Posts: 1,127
Likes: 122
From: Chico, Ca.
The dizzy is a reman with Pertronix Ignitor III and flamethrower coil. Vacuum advance is working. The push rods looked okay, when I last had it apart, but that was before the timing chain change. A leakdown test next?