[69BahamaYellow]

Does anybody have experience tuning these things. I have a 1971 2.2 911T with these carbs. The engine and carbs have been rebuilt and runs strong and gets good fuel economy. Only problem is that I have a backfire @ idle that I can't get rid of. The backfire comes back through the carbs and through the exhaust on all cylinders. It acts like it runs rich @ idle (with mixture jets @ 2.5 turns open), but I have no CO meeter to verify. Closing mixture screws a bit helps some, but I turned a few needles completely closed, and those cylinders still backfired. Opening them up doesn't do anything either. Acceleration, and any engine speed above idle is excellent (but still a little backfire under no load conditions). No matter what I do to the auxiliary enrichment devices, it still doesn't change. With all the backfiring, it's hard to hold a steady 900RPM idle. Unless I occasionally pump the throttle, the engine will eventually die, and sometimes after doing this, it takes a while for RPM to come back around 900 (throttle linkage works fine). Cam timing (original T Cams), ignition timing, valve clearance, etc. is all perfect. The carbs are absolutely spotless and it doesn't appear that they have ever been modified. I thought I could fix anything, but this one has me stumped. Anybody got any suggestions?