Still Backfiring
Thread Starter
Racer
Joined: Apr 2005
Posts: 494
Likes: 0
From: Virginia
Still Backfiring
Still trying to get my 73-350 running after a rebuild…
Installed the Proform Main Body and Throttle plate assembly on the Holley 650 DP, to eliminate any vacuum leaks from the carb. It still backfires and won’t run without backfiring. Often when it backfires the carb catches fire. There is something wrong other than just the timing. I have rebuilt many SB’s and it shouldn’t be this hard to get it running. The firing order is correct, and the vacuum lines are plugged – other than the distributor advance.
I’m currently thinking it may be:
1) A problem with the distributor: Even though the car ran fine before the rebuild, it is the original stock distributor. Bought a curve kit, going to replace the springs just to get the old ones off.
2) A problem with the valve adjustment: Can this cause backfiring?
Any help will be greatly appreciated.
Installed the Proform Main Body and Throttle plate assembly on the Holley 650 DP, to eliminate any vacuum leaks from the carb. It still backfires and won’t run without backfiring. Often when it backfires the carb catches fire. There is something wrong other than just the timing. I have rebuilt many SB’s and it shouldn’t be this hard to get it running. The firing order is correct, and the vacuum lines are plugged – other than the distributor advance.
I’m currently thinking it may be:
1) A problem with the distributor: Even though the car ran fine before the rebuild, it is the original stock distributor. Bought a curve kit, going to replace the springs just to get the old ones off.
2) A problem with the valve adjustment: Can this cause backfiring?
Any help will be greatly appreciated.
Le Mans Master
Joined: Jan 2006
Posts: 5,921
Likes: 0
From: GA "When I grow up, I'm gonna get a Trans Am and run from the cops". Direct quote from my 4yo son.
I had that problem right after a new engine install and it was the timing all out of whack. If your dist is in a tooth off or just plain out of time it will cause big time carb backfires. Backfires out the exhaust could be as simple as a misplaced plug wire.
Strong possibility, and it would be a intake valve.....
Tech Contributor
Joined: Aug 1999
Posts: 14,380
Likes: 6,391
From: At my Bar drinking and wrenching in Lafayette Colorado
Make sure you have enough timing in it. You need to be at about 18 initial with 36 total. If you have a valve too tight, it will be popping up through the carb with every firing stroke of that cylinder. If it just pops when you flick the throttle, you have a timing problem or a lean condition.
BTW - there is no such thing as being "off one tooth." Timing can be correctly set regardless of where the distributor is dropped in. If it's off a tooth, it only changes the installed orientation of the distributor body once you set the timing right. It does not affect timing or performance.
BTW - there is no such thing as being "off one tooth." Timing can be correctly set regardless of where the distributor is dropped in. If it's off a tooth, it only changes the installed orientation of the distributor body once you set the timing right. It does not affect timing or performance.
Pro
Joined: Sep 2006
Posts: 671
Likes: 0
From: McCook Nebraska
If you just stabbed the distributor and are trying to get it to fire and it is backfiring, it sounds like the distributer is 180 out. If it has been running and backfiring, check to see if you have a cracked distributer cap.
Melting Slicks
Joined: Mar 2005
Posts: 2,838
Likes: 10
From: Austin TX
An engine wouldn't run if the distributor was off 180 degrees. When one is firing, six is finishing it's exhaust stroke.
Might look for a broken valve spring(s). Also, if your harmonic ring has spun your timing could be way off. Might do a static setting.
When does she backfire through the carb,..on start-up? Accelerating? Cruise?
Might look for a broken valve spring(s). Also, if your harmonic ring has spun your timing could be way off. Might do a static setting.
When does she backfire through the carb,..on start-up? Accelerating? Cruise?
