White puff of smoke!
 

After a long straight I let off and I get a white puff "cloud" of smoke. Any suggestions? p/v not closing? too hot? timing? Need help quick. thanks

Ron,

If its only during a high RPM/closed throttle condition, then vacuum is higher(compression braking). This means you could be pulling in coolant or trans oil. Any other symptoms? Coolant or trans oil contaminated?

If it happens when the throttle is opened after a hard decel then it couild simply be cleaning out after loading up from a rich pilot, but I'm sure you know this.

42 pilot 172 main, fluids seem fine but I will look again today, could it be the p/v not closing fast enough. The bike seems to run really really good plug looks brown/ not white or black. I just started noticing it the last 2 rides. Note: junior is really riding the bike. Never noticed in the woods but have noticed the last two times on an mx track. Any help will be mint as we have a netra scramble sunday. thanks guys

I don't see how the PV would cause that. I guess you have to be sure exactly when its happening, closed or closed then opened throttle. From my experience its typical after a long technical decent mostly off throttle and then hard accel, simply burning off extra fuel/oil, even on a cleanly jetted bike. Should be able to tell if the smoke is from two stroke oil or if its different. If you have a leak down tester in the shop that will tell you for sure.

I will get a leak down tester on order today, it looks and seems to be only from full throttle then letting off. "Wide open to nothing", it puffs a pretty big cloud when he gets back on the gas it goes away. I will replace head orings and w/p seal today but it does not seem to be loosing fluid. thanks again for the input.

It won't be the waterpump seal so save your time, the trans side of the seal sees no pressure change from throttle position. Head o-rings/base gasket if its coolant, crank seal/center case gasket if its trans oil. Also check if your trans/PV vent is clear, if blocked you could build pressure and push a compromised seal over the edge.

I would guess O-ring...Have you had the head off lately?
Like Glen has suggested leak down test.

thanks I will check all of the above