Yamaha 9.9 fuel in crankcase

[nuthinbutnet]

I have a 1990 FT9.9ELD 4 stroke long shaft tiller<br />outboard motor that is taking on fuel in the crankcase.(oil and water do not mix) I replaced the diaphram and the round rubber valve in the fuel pump, but am still taking on fuel. It does not appear to be flooding. The motor idles / runs fine, but the green oil pressure light goes out. I can't find any cracks or holes in the fuel pump housing. I run the motor just about at idle for trolling.<br />Any suggestions?

 

[JB]

Re: Yamaha 9.9 fuel in crankcase

Howdy, NBN.<br /><br />Welcome to iboats. <br /><br />Your engine could be running too cold and therefore too rich. That has caused your problem in larger, EFI 4 strokes. That could be caused by a stuck-open thermostat.<br /><br />I would carefully check the float level setting in the carb, do a leakdown and compression check to verify that it isn't being caused by blowby or valve guide wear, and then investigate the complex cold enrichment system for leaking vacuum lines or failed temp sensors.<br /><br />I no longer have my Service Manual on that engine, but I do recall that the automatic cold enrichment system is a nightmare of technological overkill.<br /><br />Good luck, and let us know what you find.

 

[nuthinbutnet]

Re: Yamaha 9.9 fuel in crankcase

It's been a while but I just did recently solve the issue on this motor making oil. Apparently the previous owner thought it was a good idea to drill out the carburator jet to a larger size. I replaced the jet and it runs great without fuel in the crankcase, or black buildup on the transom at the waterline...