Yamaha 4 stroke F2.5A outboard burning oil

[Ngoodall]

Yamaha F2.5A Outboard stored over winter upright and now noticing from time to time large amounts of smoke and oil coming out exhaust. Thought it could be fuel so replaced fuel that was c in it from last year. Engine starts fine and can go for minutes running ok. When I pull the plug it looks OK. However when it starts producing smoke and oil droplets from the exhaust the plug is then all oiled up.
This link below is a 10 sec video that demonstrates this New video · Monday, Jun 2 ð¬

Video starts with the engine already running for about 30 seconds at nearly full throttle (it's at temperature as this is one of many experiments! ). Just less than 5 seconds into the video (35 seconds after starting it) the engine slows and the smoke starts. I haven't touched the throttle or anything else on the engine. It sometimes clears itself in 10 to 30 seconds but tends to start coming back more frequently after that.
Taking throttle all the way back to tick over clears it after a few seconds. But any throttle above the start position results in this behaviour, though think the higher the throttle the quicker and more frequently it happens. The head gasket seems OK, no obvious leaks. Don't have a compression guage. No water in oil.
Only thing I can think of is piston ring or oil seal, but don't understand why it's intermittent

New video · Monday, Jun 2 ð¬

 

[snowbird30ds]

Crankcase breather partly blocked resulting in a burst of oil into the carb as the crankcase pressurises then clearing as it burns off?

 

[Ngoodall]

Thanks for the suggestion. I pulled off the various pipes from the crankcase and intake silencer, blew them all through, though not a lot came out. l also poked pipe cleaner down the various pipe connectors on the crankcase. Put it all back together and now it's running perfectly. Must have been some sort of partial blockage as you suggested. One that I'll remember for the future!

Nick

 

[Paul1962]

Yamaha F2.5A Outboard stored over winter upright and now noticing from time to time large amounts of smoke and oil coming out exhaust. Thought it could be fuel so replaced fuel that was c in it from last year. Engine starts fine and can go for minutes running ok. When I pull the plug it looks OK. However when it starts producing smoke and oil droplets from the exhaust the plug is then all oiled up.
This link below is a 10 sec video that demonstrates this New video · Monday, Jun 2 ð¬

Video starts with the engine already running for about 30 seconds at nearly full throttle (it's at temperature as this is one of many experiments! ). Just less than 5 seconds into the video (35 seconds after starting it) the engine slows and the smoke starts. I haven't touched the throttle or anything else on the engine. It sometimes clears itself in 10 to 30 seconds but tends to start coming back more frequently after that.
Taking throttle all the way back to tick over clears it after a few seconds. But any throttle above the start position results in this behaviour, though think the higher the throttle the quicker and more frequently it happens. The head gasket seems OK, no obvious leaks. Don't have a compression guage. No water in oil.
Only thing I can think of is piston ring or oil seal, but don't understand why it's intermittent

New video · Monday, Jun 2 ð¬

Is it Overful of Oil??