For about four days, four aborted trips to the field and a headache, one of my NCs' would run wide open for a few seconds and then go into a popping mode. The popping mode, for lack of a better description, was similar to a two stroke four-cycling at about one-third its power. You could pull the power back and immediately apply it, get a few seconds of full power and do the routine all over again. After a plunger assembly, diaphragm, looking at the clearance on the rear rotor, etc. we put a new bullet in and came up with the same problem! The only thing common was the NC muffler. Took it off its extension and found the inside had broken into three pieces. I fished them out, put it back together and it worked just fine, thank you! Soooo if you get this activity using a NC muffler, take a look before you blame it on the engine. EH