Re: Water Getting in Top Cylinder Yamaha 40hp Twin

[joesnuffy]

I think the fuel pump is mounted closer to the bottom cylinder. I will start with the fuel pump being possible issue first. I will by pass it as you suggested and pump the fuel bulb to see if engine runs better. The sound reducer material I used is the good stuff like a professional grade 3M style with the peel adhesive no foam nothing to get sucked in but it could have still bent a reed valve if the negative pressure was to high. If it isn’t the fuel pump then I will go and look at the reed valves and maybe re-torque crankcase halves. I have cleaned and inspected the carbs which were both working excellent I don’t think it is them. Both high and low jets were clean and both low jet screw adjustments were 1 1/2 out when engine was running as it should be so it could be I bent a reed do to my not wanting to hear a noisy engine.

This is my first experience with a Yamaha 2 stroke but it seems closely related to an OMC outboard engine which I do know. The engine has good fire on both plugs. With the choke on partially and the idle up a bit it will run and when I pull either plug wire engine will die so both cylinders are firing somewhat it just won’t get over the hump to WOT and the top cylinder looks to be getting washed by fuel or water.

Thanks for your help,
Joe

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