Hey Mark S., I think I found my popping noise. First I checked my valves like you suggested. Then I tried to tighten all the exhaust fittings. Checked compression - 120 to 125 PSI on all four. Plugs were black, but not oily. Still popping. About to order a new Pict 34 and throw away the Dual Kadron set-up. Went to the AJ Simms website and he referred to running lean causing "detonation". I don't know what that means, but popping sounds like something detonating, so I adjusted the mixture out for more fuel and like magic, no more popping. That makes sense because it started popping after the trip to Eureka Springs. I adjusted the carbs trying to improve the gas mileage. I must have gone too lean and I guess that causes - detonation - popping. I guess I will see if that takes care of it or not. Thanks, Ronnie