Ive got a 1998 MXZ with a highly modified engine. At wide open throttle engine sputters and looses a little power, when you let off intermidently backfires from exhaust? At part to half throttle it pulls real hard like it should. At first I thought it was a lean sputter but then I checked my max egts on my digitron and they were ok. Im wondering if someone can give me an idea of what is going on with my sled? I bought from a guy that snow dragged it. I think the engine work done was done by specialty sleds and mots machining, previous owner has had no problems with it. It has 15:1 comp thanks to a machined head, milled out carbs with bobs, k+N pods, custom built pipes, stubby rotary cover, Im running pure sunoco race fuel, main jets are 480 in both, needles in middle slot, my max egts are 1124,1127, which are perfect if you ask me. Although my cylinder head temp is 127 f which seems a little low, I checked ignition timing-OK, I checked secondary clutch setting for possible over revving-OK, Took carbs apart and inspected-OK, verified float hight-OK, Has anyone seen a drivability issue due to an engine running too cold?, Could a thermostat cause this concern? What should my cylinder head temp be at operating temp?, Any suggestions would be appreciated.