carb coughing
Thread Starter
Safety Car
Joined: Sep 2012
Posts: 4,688
Likes: 41
From: Palm Harbor, Florida
carb coughing
I got a 383 stroker with a new holley 750double pumper. New fuel pump. New ignition components and wires. New valve springs and a valve job. Can't get it to stop backfiring thru Carb when given enough gas.
I have a k&n type air cleaner with full size headers. Im wondering if that Carb out of the box supplies a rich enough mixture for me. Anyone here running something similar withheld no issues whatsoever ? Thanks
I have a k&n type air cleaner with full size headers. Im wondering if that Carb out of the box supplies a rich enough mixture for me. Anyone here running something similar withheld no issues whatsoever ? Thanks
Le Mans Master
Joined: Apr 1999
Posts: 6,134
Likes: 46
From: Raleigh North Carolina
Backfiring means that a spark plug is firing when it should not be firing... I.E.-when an intake valve is still open, or, if an intake valve is warped and is not sealing. I pulled an engine apart a long time ago (Ford 292) that actually had a piece of a valve head completely missing.
This not a carb problem... but an ignition or valve problem.
Some possible causes-
Spark Plug wires installed incorrectly
Spark plug wires cross-firing (usually a problem with old, oily, rotted wires)
Distributor timing off
Rotor cross/firing (carbon tracking) inside the distributor cap
Warped/damaged intake valve (least likely)
Timing gears severely worn
Timing gears installed incorrectly
Incorrect valve lash (too tight- valves not closing completely)
Did you use the "twist the pushrod" method to set valve lash?
This not a carb problem... but an ignition or valve problem.
Some possible causes-
Spark Plug wires installed incorrectly
Spark plug wires cross-firing (usually a problem with old, oily, rotted wires)
Distributor timing off
Rotor cross/firing (carbon tracking) inside the distributor cap
Warped/damaged intake valve (least likely)
Timing gears severely worn
Timing gears installed incorrectly
Incorrect valve lash (too tight- valves not closing completely)
Did you use the "twist the pushrod" method to set valve lash?
Last edited by Tom454; Jan 31, 2013 at 09:24 AM. Reason: Added causes
Thread Starter
Safety Car
Joined: Sep 2012
Posts: 4,688
Likes: 41
From: Palm Harbor, Florida
I'm wondering if there is any chance I got some crap in tank too large to come thru and see in my see thru filter but still able to maybe restrict flow enough when needed at higher rpm?
Le Mans Master
Joined: Apr 1999
Posts: 6,134
Likes: 46
From: Raleigh North Carolina
An engine cannot backfire through the carb unless there is a path between the carb and the explosion (backfire) that you hear. One or more of your "explosions" (spark plug & gas) is getting out to your ears when it should not be.
Race Director
Joined: Oct 2000
Posts: 14,996
Likes: 79
From: central FL, near the beach.
did u lap the valves and check for full contact? if not, after checking for other causes, DRIVE IT.
will clear up as u go, all better within 50 miles. That is the plan. good luck!
(valves not lapped will usually seat in operation)
will clear up as u go, all better within 50 miles. That is the plan. good luck!
(valves not lapped will usually seat in operation)
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Thread Starter
Safety Car
Joined: Sep 2012
Posts: 4,688
Likes: 41
From: Palm Harbor, Florida
When I changed springs last night and sent compressed air thru spark plug hole, I did have a very small amount of air leakage. I only hand tightened the rubber hose with the fitting on end. I hoped the air was seeping out of spark plug hole... it did it on every one though.
Thread Starter
Safety Car
Joined: Sep 2012
Posts: 4,688
Likes: 41
From: Palm Harbor, Florida
finally found my problem! I swapped out some older wires in place of fairly new MSD. ran like a champ. so when I got back home took the wire "sorters" off and the two heat shields that I had on number 1 and number 7 boots, all cracked and corroded, they were shorting to the headers....wow, can't believe this if finally done.
Thread Starter
Safety Car
Joined: Sep 2012
Posts: 4,688
Likes: 41
From: Palm Harbor, Florida
runs like a new engine! idles great, runs smooth, life is good, I have no idea on the cam(bough engine used locally)(my spark plug wires)....lol, thanks for help guys.
Matt, I did your "drive it" thing for a little bit and thought to myself as I probably got to about 30-40 miles, "this is not fixing it, this car sucks!"
Matt, I did your "drive it" thing for a little bit and thought to myself as I probably got to about 30-40 miles, "this is not fixing it, this car sucks!"
