Here's the scoop. I finally figured out that it isn't blowing oil into the airbox, like I thought--the air tube was clean, no oil. Therefore, not blowing oil through it.
I took it in to have the valves, belt and brakes checked and mentioned the oil usage problem. They did a blow-by test and determined it's leaking a little around the rings. Not enought to be a problem, in and of itself, but not an easy fix, either. Apparently, the cylinder is slightly out of round from wear. The mechanic called his contact at Yamaha and they confirmed that it's a problem on the 660 engine. (He also adjusted the valves, which may help some if it was experiencing both problems. Regardless of whether adjusting the valves reduces the oil loss, it starts easier and is less cold blooded--both are good things!) (Belt was fine, brakes all got replaced)
The "fix?" $500 to bore it and put in a new piston. And it will stay fixed until it wears, again. Sounds like a job for next winter since I'm sure it will take a week or two--they ship the cylinders out to have them ground.
And, since I had some trouble with overheating last summer, I'll wait until I'm sure that problem is solved before I get it bored. I'm hoping to keep it cool by keeping the radiator cleaner. If that doesn't do the job it's getting a High Lifter radiator kit early this summer--like, right after it overheats the first time. I'll be pulling a trailer on a couple camping trips this summer and an overheating engine just won't do at all.
In the meantime, I check the oil religously and keep adding to it.
Bummer, dude.
