I'm kinda a mechanic but just wondering options before taking apart in a few weeks( money on boat). My 2004 400cc yamaha big bear just started smoking very bad for no reason. Piston rings when they go motor lets out gradual small puffs of smoke and with time gets worse. But in my case no smoke at all, just one big black carbon puff of smoke (buddy saw behind me) now its madness...I'm thinking valve seal let go and valve stem has ware letting more oil in. Lots of compression with just pull starting feal. I put synthetic oil in it about 2 weeks before this happen..could that of messed piston rings?