How do bad crank seals (left or right side) affect a two stroke? Vacuum leak? Any experiences? Thanx

In my experience a left side (ignition side) leak will cause your bike to run lean. If its bad it can run very lean and potentially seize. If you take the flywheel and ignition off you can sometimes see it leaking oil. Some bikes you can replace it from the outside, some you have to replace from the inside which sucks cause you have to split the cases to do it.

A right seal leak I've never had, but I understand that this is a wet seal between the crankacase and the gearbox. So when it leaks the bike sucks in oil which causes the bike to run rich - I think.

There's a good thread or article on eric gorr's site about this. I was just reading it, but don't remember exactly where.

While sitting unused (not running) the oil can seep into the crank (past the right crank seal) which causes a lot of smoke to exit the tailpipe for the first few minutes after starting it. While its running you'll be getting more oil to the engine parts but it won't change the jetting (rich/lean).

Just changed my right seal..On a Yamaha the clutch basket drive gear would appear to throw a stream of oil right at the seal while running. It would be easy for the motor to suck the oil in.

I rode about 10-15 laps and a few starts at a practice track. It lost 150cc (put in 650cc and measured only 500cc coming out after the ride) oil in that short time, so I decided to replace it. It did smoke, but not as much as I would have thought. Smoke was white.