A friends Bullet 500 AVL suddenly started puking oil out the crankcase vent during a ride. He made it home with with just enough oil to cover the bottom of the dip stick. So I ride up to SF with a filter kit, we drain everything, check his screen and mag plug. No discrepancies noted. Installed the plugs, drained the oil, changed the filter, and serviced the oil to the middle of the hash marks. Ran the beast for a few minutes noting the excessive spray out the vent hose.
All the hoses and catch-can had been removed when I modded his bike a couple years ago. At that time the vent hose was made shorter and a duckbill added, then positioned over the primary to lube his chain.
For two years no problems (other than the time he did his own oil change and filled it to the top of the hask marks
). We got 3 feet of hose from AutoZone, attached it to the vent and routed it back over the rear mudgourd stay, then ran the engine. At idle all the way through full throttle not a drop came out, even after 10 minutes at 3/4 throttle.Had him take it for a 4 mile ride to put a decent load on the engine, and by the time he returned it was still pissing oil.With the exception of my carb upgrade our AVLs are virtually identical, so I'm at a loss to figure this out. Other than the time he over-filled his oil he's had zero problems, and the engine runs beautifully except for the puking.
Any suggestions? I'd like to save him the $$$ he'll need to spend if he takes to Mark at OCD to fix it.
What would cause that kind over-pressurization in the crank case when the oil level is correct?