backfire

[Wolfhound]

I have a 1969 912 with a rebuilt engine, carbs, optical ignition & coil, and exhaust. The problem is the car backfires fairly frequently when I have accelerated and then let off the gas. This occurred before and after the carb rebuild, ignition installation, and exhaust installation. Very loud. Plugs and wires are good, the car runs fine, no other obvious problems. Help.

[Nige-912E]

gotta be an air leak either in the exhaust system or inlet side of things.

Start engine and check for any amount of blowing around joints

[912s]

Backfiring during deceleration is most commonly a vaccuum leak, but can also be caused carbs that aren't in sync or by worn out mixture screws which probably weren't part of your carb rebuild?

[lapuwali]

Retarded ignition timing can also cause backfires like this.

[rgruppe 912]

my generator and alternator went bad and at the same time my timing. i messed with the carbs and got them out of sync because i didn't know the timing went out of whack when i installed the new parts. Turns out that was why it had no power and was backfiring.