Expert: tyler boehner - 3/5/2008

Question
I have re-built this motor, it curently has 115# comperssion in all 6 cyl +/- 3# I have cleaned all passageways in carbs when installing a re-build kit. It curently runs well in the driveway with ear muff on (supplying the Motor water). It goes into gear revs up as all is well. When I put the boat in the lake it starts great, idels smothly, but when I put it into gear it stall right out. One time I got it to go into gear and rev a couple of seconds then stalled out not having much power, this testing was doen with the boat still on the trailer backed into the water at the boat ramp. I do have spare parts, I got 3 motors the same era when I started this project. trying to get one good one. (they all had blown pistons). I do not want to repalce all electrical items at the same time. What would you change first? Stator? (but that is the hardest to change). Your thoughts Please....

Answer
A compression test can lie about the shape of a two stroke motor.  To test the pistons I would do what is called a leak down test.  That will tell you a lot more about the engine and if the pistons are sealing like they should.  When you run a boat on the hose, the rpm will be much different than when you put the motor in the water.  You should put the motor in a test tank or back it down the ramp then reset your timing and your carbs.  On the hose, motors run a lot higher rpm and seem to be running smooth but once you put the exhaust back pressure on the motor by submerging the gear case it will change the way the motor idles and runs.