Yamaha 1997 4 stroke gas in the oil

[dandj]

this has happened twice in two years, motor has less than 20 hrs. when i pull the oil dip stick , oil and gas over flow all over the place. the motor runs,for two min or so then stalls. help !!

[rodbolt]

hello sounds like a sicking needle valve due to nasty gas. 20 hours in 2 years is almost neglect . clean all needle seat assymblies and try it again. good luck and keep posting

[JB]

Howdy DandJ.This is not at all uncommon in Yamaha 4 stroke powerheads (including Mercs).According to Yamaha research, it is caused by the engine running too cool, and therefore too rich.Replace the thermostat, then break the engine in again. Run it hard for several hours.Good luck.

[maclavin]

Check to make sure the fuel pump diaphram isn't bad also.