Hello there,
I need a little support on my 72 chevelle.
Whats the best way to track down a backfire thru the exhaust?
the motor is probably a 73-74 454 with a new holley 650 with a
hei ignition. I've adjusted the timing to spec, 10 btdc then advanced.
brand new accel 8mm wires, and a cap and rotor, the plugs looked fine.
I get a back fire during accelaration(either a loud bang or a mellow putt-putt). Even idling I can hear
a slight mis-fire. I've only had the car a year and don't much of its history.
I'm wondering if it might be my hei module, cross fire thru the aftermarket wires
or a coil gone haywire. Is there a checklist I might follow to find the problem
:confused:
THANKS IN ADVANCE
RODNEY - '72 CHEVELLE CONVERTIBLE
454 -4SPEED MUNCIE WHITE W'BLACK STRIPES

You have a pretty good list for starters...I would only add that you may also check the valve lash (specifically the exhaust side) to make sure it isn't too tight. If you are holding the valve off the seat a little bit, this can lead to a backfire and also to the valve burning up in short order.

Also be sure that when you adjust the timing the vacuum advance is disconnected, and plugged.
Best of luck,
Brandon