55HP Yamaha 2 Stroke Manifold Check Valve

[ChuckB1954]

Engine running rough at idle and dies. When I remove the number 2 spark plug, it is always fouled with oil. I noticed that on the number 2 carburetor there is a hose (#12) coming off the intake manifold going to a check valve (#3). When I remove the hose off the manifold going to the check valve and start the engine, oil spurts out. It seems to me that the engine is sucking oil through the manifold and causing the plug to foul.(?) When I blow into the line going to the check valve, it is blocked, but when I suck on the hose, oil comes out (yuck!). The same stem coming out of the number 1 manifold is blocked with a rubber sleeve. Does this sound right? What is the purpose of this check valve? Where is this oil coming from?


Check Valve.JPG

[99yam40]

not sure on this motor looking at the parts breakdown, but crank case re-circulation check valves and the lines attached to them usually pull pooled liquid oil/fuel residue out of the crankcase and route it to be burned

[ChuckB1954]

Maybe a lot oil has been accumulated from the engine sitting and during assembly? Maybe the engine just needs to be ran at high RPM's (?) Or ran with the hose off and the manifold plugged up to get rid of the excess?

[99yam40]

how is it going to go away if you disconnect what is suppose to suck it out and plug it.
kind of like the other line you mentioned, why is it plugged off?

[ChuckB1954]

how is it going to go away if you disconnect what is suppose to suck it out and plug it.
kind of like the other line you mentioned, why is it plugged off?

If you re-read the original post you will see that the hose coming from the crankcase check valve is blowing oil out of the crankcase that is then getting sucked naturally into the intake. By disconnecting the hose, it might blow out the excess oil. Plugging up the manifold hole temporary will stop what would be a vacuum leak.