85 RX-7 12A, back fires badly on acceleration
 

I have a 1985 Mazda RX-7, 12A engine, manual transmission. The car back fires badly! This is especially bad if I am accelerating and then let off the gas, but may even do it if I am just cruising and then let off the gas.

I've already had suggestions (but no firm diagnosis) that it could be the air control valve ($450 aftermarket) or an "air supply tube" somewhere - whatever that could be.

Do either of these suggestions sound reasonable? Could it be anything else?

I have noticed that this does NOT happen when the car is cold and the choke is engaged.


Thanks

RE: 85 RX-7 12A, back fires badly on acceleration
 

Several years ago I had a simular experience with one of my 12a's backfiring out the exhaust. It was difficult to diag becouse my condition was intermittent. I lucked out and was able to isolate the cause to worn ignition lock cylinder contacts on the back side of the lock cylinder. The worn lock cylinder would turn off the ignition just long enough to load up the exhaust with fuel then turn it back on and .......KABLAMO !!!!! It was a real heart stopper when that little sucker went off. You could see peeps on the sidewalk jump out of there skins as it sounded just like a highpower rifle going off. I had a fun roadtrip up and down the hills in Seattle once befor I was able to make the repair (lots of peeps on the side walks) Hehe .

Im not saying that this the fix for your backfire concern but its something to check befor droppin the big coin.