Topic: Oil pouring out of oil tank vent (Problem Fixed ) Thanks

[74honda750]

Hello. I am haveing a problem with oil pouring out of the
oil tank vent at high rpms. I can tell you a few thing about
the the bike. It is a 1973 cb750 with 8800 miles. The bike
had been sitting for 12 years and three of those out side.
After I got it running I changed the oil with amsoil 10-w40
synthetic. went on first ride and when I got back found oil
leaking from tank vent. Drained oil from tank and then removed
and cleaned the tank and blew air into all hoses and openings.

Put it all back together and ran the bike on center stand at
4000  to 5000 rpm and looked into the oil tank and could see
the oil splashing up and over the vent tank. Can't figure out why
the oil does not drain into the crank case. Any clues  
   

[rhinoracer]

This is too obvious but I'm gonna ask anyway. Could the oil level be too high?

[nteek754]

Hey there 74 just a thought check your valve cover vent hose, making sure it isnt pluged or crimped. I would be curious of the oil presure, I run gauges on most of my bikes .Good luck keep us posted Craig in Maine

[TwoTired]

High RPM is where piston ring blow-by is the most severe.  This allows the crankcase to build pressure and that escapes out the engine breather tube.  The oil tank is connected to the engine breather.

Have you done a cylinder compression test yet?  Even more telling about a blow-by condition, would be a leak down test.

Cheers,