cj5, 304 backfiring in carb

74 model with a 304 and it idles well but if I accelerate fast it will badkfire in carb repeatedly but will eventually speed up. I installed a new timing chain and gear while body was off six months ago. I also rebuilt carb too. the timing is set a 3 degrees btdc , dwell at 30 degrees and rpm at idle is at 750. there is an old post with same symptoms but does not say if problem was fixed. they thought that the coil may be the problem, anyone have an opinion? the accelerator pump appears to be working also,with engine off I can push accelerator rod and see gas being squirted down carb. thanks for any help.

 

Usually a backfire through the carb means the timing is out, double checkyour settings

 

x2 with the timing issu...

 

thanks for the suggestions, I checked timing this morning and it was still on 3 degrees btdc. It didn't backfire at all until it had run for about 8 minutes. I'll go pull #1 plug and get piston to top on comp. stroke and look at timing mark. thanks.

 

The thing about timing is unless you’ve gone through and degreed your motor you don’t know exactly where the true top dead center is and it can be several degrees off of where the timing marks end up. That’s why I prefer tuning timing by ear and using a timing light just to see where that left the timing mark.
As for your 304, I don’t know that much about them but 3 Deg. BTDC isn’t much. I doubt it would hurt anything to advance that a few degrees and see how she runs.

 

If it was a Buick v6 and it was popping through the carb it would most likely have a flat lobe on the cam. I am not an AMC motor guy, but that may be your issue there also.

 

Not sure what distributor you have, but with my 304 I originally had the prestolite and the ignition module was causing backfires. Once I upgraded to HEI, I haven't had the problem since.

 

thanks for all the responses, I had lots of problems. I read the manual on carburators and learned that i needed to adjust the mixture screws all the way in and 2 revolutions out. My timing was off, when at tdc the rotar was not on #1 in distributor cap, and I had 2 plugs not firing. Waiting on parts store to open to get dist. cap. I'm having lots of fun playing with this thing.