backfiring

[MEK-Dangerfield]

Incorrect timing can cause backfire. You are assuming the vacuum advance is working properly.

I agree with you on the incorrect timing part. 

When you nail the gas pedal, your vacuum advance will be at zero. So that's why I think the problem is elsewhere.

[cudabob496]

I agree with you on the incorrect timing part. 

When you nail the gas pedal, your vacuum advance will be at zero. So that's why I think the problem is elsewhere.

Yes, the vacuum advance will be zero, if it is working properly. My old Mopar vacuum advance would
not always go to zero, so I ended up chucking it.  So to eliminate the possibility of the vacuum advance
being a problem, I suggested unhooking it.

[MEK-Dangerfield]

Yes, the vacuum advance will be zero, if it is working properly. My old Mopar vacuum advance would
not always go to zero, so I ended up chucking it.  So to eliminate the possibility of the vacuum advance
being a problem, I suggested unhooking it.

Wow!

 OK, I see what you are saying now. Just be sure to plug the carb. port, or you will be sucking in air.

[cudaaah]

Haven't been on the site for awhile, obviously.  To update, I took the car to my engine builder. After putting new ignition parts in, timing was good, carbs good,  it was still backfiring.

Finally checking the distributor itself, he found a small brass tab broken off inside the distributor itself, I seem to remember him saying it had something to do w/ the timing advance.  Heand said it looked like someone had shoved a screw driver in.  Needless to say I made a mistake going to the local "EXPERT".

Thanks all for the help
Live and learn...there's an expert in every garage

[cudabob496]

Good to hear! Timing may have been good at idle, but should be checked throughout the rpm range.