So i bought an 86 moto4 yfm 200 and i seem to be getting a lot of blow by (thick exhaust cloud during acceleration). Anyone have experience with this? Causes? Where i could find new parts? I looked online. Can find jug and piston kits for a 225 but not a 200.

 

Unless the head gasket has gone, it looks like the rings are worn, probably the bore too. Can be valve seals, but they usually give more smoke on start up and the overrun than acceleration. New rings are available, so the best way is to take the top end down, measure the bore and find out if you can get away with just fitting new rings to the existing bore and piston. If it does need a re-bore, someone may have an old stock oversize piston or, if the bore was standard, a new cylinder and rings fitted to the old piston. Rather an expensive way to do it, but needs must.