Fuel geyser from crankcase

2000 50hp. Noticed motor was looking wet and oily, about a foot below cowling on rear. Popped cowling and all looked good. Pulled oil dipstick out and got a geyser of fuel and oil , took about 20-30 seconds for it all to stop flowing out.

Carbs services about 4 weeks ago. we last used boat about 2 weeks ago and it ran like a champ. Had a full tank of gas and only ran motor for 45 minutes or so. Boat has been stored outside and we’ve experienced 100 degree temps lately.

I have a theory what the issue might be, but wanted to see what everyone else had to say.

I’m thinking that with hot temps, fuel tank pretty much full, the gas expanded, and pushed its way past the carbs, which would imply the vent on fuel tank is not working.

A 2000 50 HP Yam does not have a dip stick. I suspect that you have an F50. A four stroke. That F is very important.

You seem to have what is known as a motor "making oil". Fuel dilution into the crank case.

Cause can result from being over propped, excessively cold water operations, excessive idling, thermostat stuck open, carbon buildup on piston rings, excessively rich air/fuel mixtures and ...