Oil forced back into tank??

[Cliff]

Just noticed this on my 1977 GT750. When I rev the engine up to 5000-6000 rpm, it looks like injector oil is being forced back into the reservoir! Any ideas/what to look for??

[GT750Battleship]

I wouldn't have thought that possible,the lines have the one way spring/ball arrangement ? Have you done any work on the pump recently ?
look forward to reading other people's thoughts on your post!
Regards,
GT750Battleship

[ISR64]

Sounds like contamination of the check valves to me, allowing crank pressure to push back up the lines, is 2T oil seeping into the crank when the bike is parked up for a period. Personally would be worried about running like this, crank not getting lubrication at higher revs.

[Knut]

Sounds like contamination of the check valves to me, allowing crank pressure to push back up the lines, is 2T oil seeping into the crank when the bike is parked up for a period. Personally would be worried about running like this, crank not getting lubrication at higher revs.

My H1 had a crank seize due to the same thing. Large air bubble in one oil line due to return pressure from the crank case caused by a faulty check valve.

[yeadon_m]

Please check hat the oil tank cap is venting - if not, it may appear that oil flow is reversing when what is happening is a partial vacuum in the tank! Mike

[Blokhead]

Mine appeared to to the same thing. I took the pump apart, and found a tiny piece of white plastic inside (maybe from the tank? ), and O-rings in the octopus permanently squashed. New paper gasket, and O-rings, and all appears to be well. Glad I was running some premix in the tank at the time.