I have Holley carb& can make ajustment so that it won't back fire at Idle. But it won't run right open road. When I ajust for that it won't Idle. This isn't a real hard back fire. It through the carb & not the EX.

Backfire are usually detonation issues associated with timing. I would take a good look at the distrubutor first. If your sure all is in order then go to the carb. Next, go to your nearest speed shop and buy the Holly tuning manual. It is a must have for anyone who thinks they know what they are doing with a Holley. I learned a bunch and was humbled by what I didn't know. You may have a power valve issue, or just a plain old dirty carb. Good luck

My experience with a backfire thru the carb. is a exhaust rocker broke, and cause the exhaust valve isnt opening it takes the next best way out, thru the carb. when the intake valve is open.

Back fire is just that, firing of the air/fuel mixture back up the intake tract, past the crab butterflys. Nothing to do with detonation.

Most common causes of back-fire are retarded timing and too lean carb jetting. What intial timing are you usiing, and are you sure all the valves are adjusted correctly?? If only one intake valve is not adjusted so it will completely close, back-fire can and will happen on that cylinder, like having a burned intake valve.

A vacuum guage would show a wildly fluctuating needle if one of the intakes were adjusted too tight, not letting the valve completely close.

Might confirm the initial timing is 12 degrees or so, with the vacuum advance dis-connected.

Back-fire can also be caused by an air leak in the carb, intake or any gasket for same.

Check this stuff out, and if you don't find a cause, let us know and we'll go on from there.

I'm not sure the valves are ajusted right. I will get out this weekend and check all the things that have been posted and let you know what I've found. Thank You.

Just got back in from ajusting the valves it worked. Thanks