Backfiring Problem...any suggestions?
Le Mans Master
Joined: May 2006
Posts: 9,993
Likes: 1,136
From: League City Tx
Yes timing can cause backfiring BUT a jacked carb can also cause backfiring. Recently, I was having a backfiring problem at WOT or even a quick half throttle stab. I changed the plugs/wires/cap/rotor and set the timing to 36* total by 3000rpms and it would still do it. That led me to believe it was a carb problem. It wasn't the original q-jet so I went and bought a rebuilt q-jet and stuck it on and the problem instantly went away. It must have had a clogged circuit/jet or something because the accelerator pump was working good.
Check your timing first, then look at the carb. If its been sitting a while, the carb is probably clogged with varnish.
Check your timing first, then look at the carb. If its been sitting a while, the carb is probably clogged with varnish.
?????
Thread Starter
Intermediate
Joined: May 2006
Posts: 44
Likes: 0
From: Spring Valley California
Ive removed and cleaned the carb/intake manifold and replaced all gaskets and parts. blew out everyhole and orifice. installed new plugs, wires, distributor, etc. verified the timing and the firing order (also made sure the wires were going to the correct spots). ive done everything to the fuel system except replace the fuep pump which when optested works fine. im convinced it is the engine, i.e. a valve or ring problem or something. seems like its the most suspect since i literally had it runing fine one day and the next it ran like crap. thanks for all the suggestions.
Le Mans Master
Joined: Jan 2006
Posts: 9,192
Likes: 27
From: Boca Raton Florida
OK, Basics:
Set timing by verifying TDC on the #1 piston, with the #1 at TDC the timing mark mark should be at -8 to -12 degrees after TDC on the indicator plate. Set the distributor to point exactly at the #1 tower on the dist cap. (this means the timing will be at 8* to 12* before at idle.
If when you set #1 to TDC the mark on the balancer is NOT after the Zero mark, your balancer ring has slipped.
If thats ok, start it up, connect vac gauge, IS it steady? If not, major vac leak, If yes, what is it at?
Set timing at 10* before at idle of about 850 with vacume adv disconnected and plugged.
Readjust the Idle mix according to the sticky at the top up there by Barry, he has a link in there to the Lars paper, this is your bible, read and follow, if you do not get the results indicated at each step, something is wrong, stop at that point and investigate and repost.
Good luck
Set timing by verifying TDC on the #1 piston, with the #1 at TDC the timing mark mark should be at -8 to -12 degrees after TDC on the indicator plate. Set the distributor to point exactly at the #1 tower on the dist cap. (this means the timing will be at 8* to 12* before at idle.
If when you set #1 to TDC the mark on the balancer is NOT after the Zero mark, your balancer ring has slipped.
If thats ok, start it up, connect vac gauge, IS it steady? If not, major vac leak, If yes, what is it at?
Set timing at 10* before at idle of about 850 with vacume adv disconnected and plugged.
Readjust the Idle mix according to the sticky at the top up there by Barry, he has a link in there to the Lars paper, this is your bible, read and follow, if you do not get the results indicated at each step, something is wrong, stop at that point and investigate and repost.
Good luck
