its definitely a pop, sounds like my shotgun behind me. what exactly does drop the clip on the needle mean? i have it on the 4th groove so do i go to the 3rd or 5th? as far as the main jet the exhaust pipe is ridiculously sooty after a 15 minute ride, i have to pull the spark plug though i guess to read the burn. does the fuel mixture screw effect this? could I just adjust that?

 

Your pipe may be the cause of that. These things are actually suppose to backfire to a degree. On MX bikes, being they have louder pipes, you constantly hear them backfire and sputter when leaving off the gas. That is what the air injection is for on our machines. It puts more fresh air into the exhaust to add to the extra unburnt fuel in the exhaust so it burns more of it cleaner.

What happens is your giving the bike gas, then leaving off to an idle position flooding the engine for a second and it blows all that gas out into the exhaust. I'm kinda perplexed to be honest, because to look at your setup I'd say your main jet is too lean actually. Your in dirty jersey so your at or near sea level, you got a UNI filter, no snorkel and a pipe (make sure your pipe has no leaks as they will amplify backfires). And I don't know what pilot your running but being you got a pipe and low altitude I'd imagine you need at least a 38 pilot,.........just as a guess. I think your needle is way too rich. I think that may be where your problem is from, I would put it in the middle position (3rd groove). That main jet does mess with my head though. I would think you'd have the 128 in there.

ALso, what the heck is an M7 pipe? Sounds like something from Pro Circuit, if so those are one of the loudest pipes, or so I hear. If thats true that would explain your popping right there, as I roundabout stated before. Also, is your air injection still hooked up? If not you may want to put it back on there and see if that stops it.
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M7.The "bling" version none of us can afford.