360 Timing
Post Fiend
Joined: Mar 2004
Posts: 6,056
Likes: 8
From: Union, Washington
I've been working on a '71 F250 with a 390. It has a Holley 670 Truck avenger carb.
it likes to backfire when deccelerating. I rejetted the carb down 2 sizes (4,300 ft. elev.)
Replace carb manifold and spacer gaskets. When I set the timing, I used a vaccum guage and advanced it until I got the best reading and it idled the smoothest. ( Same process was used when I adjusted the the carb idle mixture screws.)
But the timing, at idle is like 25* advanced and still will backfire on decell. Not nearly as bad as before.
Any ideas?
(sorry for hi-jacking this thread)
it likes to backfire when deccelerating. I rejetted the carb down 2 sizes (4,300 ft. elev.)
Replace carb manifold and spacer gaskets. When I set the timing, I used a vaccum guage and advanced it until I got the best reading and it idled the smoothest. ( Same process was used when I adjusted the the carb idle mixture screws.)
But the timing, at idle is like 25* advanced and still will backfire on decell. Not nearly as bad as before.
Any ideas?
(sorry for hi-jacking this thread)
FYI, vacuum timing is not a good way to go and will contribute to your to lean condition.
Junior User
Joined: Sep 2005
Posts: 75
Likes: 0
From: Fort Rock, OR
I reset the timing to 10*, visually checked the mechanical advance and replaced the power valve. But it still backfires.
Could it be a combination of an oversized carburetor, low compression, and some exhaust leaks in the headers?
Could it be a combination of an oversized carburetor, low compression, and some exhaust leaks in the headers?
Post Fiend
Joined: Mar 2004
Posts: 6,056
Likes: 8
From: Union, Washington
Sounds more like a timing chain jump issue that anything else.
Post Fiend
Joined: Mar 2004
Posts: 6,056
Likes: 8
From: Union, Washington
The best way is to pull the water pump and timing cover and check the timing sprocket alignment. I already explained the dial indicator method.
Thread
Thread Starter
Forum
Replies
Last Post
stevieweevie
1987 - 1996 F150 & Larger F-Series Trucks
14
Oct 7, 2022 01:43 PM
Galendor
1980 - 1986 Bullnose F100, F150 & Larger F-Series Trucks
20
May 25, 2016 01:44 PM
84respass
1980 - 1986 Bullnose F100, F150 & Larger F-Series Trucks
7
Oct 5, 2010 10:09 PM
Argess
FE & FT Big Block V8 (332, 352, 360, 390, 406, 410, 427, 428)
6
Jul 9, 2009 07:11 PM
andrewasl
1967 - 1972 F-100 & Larger F-Series Trucks
8
May 25, 2009 12:21 AM
