My friends and I are stumped. 3 weeks ago, running WOT, engine felt like prop ran into a wet blanket. Limped home. Only running on 1 cylinder. Compression checked, A-OK. Cleaned out carbs,found some junk, now running on both cylinders but with regular interval backfire or lean cough through exhaust. Pulling out choke, backfire/cough stops and engine runs smoother. Makes us think running too lean. Swapped both carbs with a complete spare set, EXACT same symptoms...running rough and coughing through exhaust. Replaced fuel and fuel filters, same symptoms. Why would some junk in one of the carbs that shut down 1 cylinder, when rectified, now cause this backfire/cough? Where else should we look? Could fuel pump diaphragm be torn....something to do with the timing...etc? Any help would be appreciated. Thanks in advance.
