[erocahoe]

"hi i have 20 foot pontoon boat that had a 65hp force that slung a rod.I found and put on a johnson 115 hp. when i took it to the river i could start throttling up and you could feel the acc. but when i would get TO A CERTAIN SPEED IT WOULD SOUND LIKE MY MOTOR COME OUT OF GEAR ? SOUNDED LIKE IT WOULD REV HIGHER AND WOULD LOSE SPEED MORE THAN GAIN.I PUT THE NEW MOTOR IN THE SAME MOUNTING HOLES AS THE OLD ONE. WHAT SHOULD I TRY FIRST TO FIX IT ,WOULD RAISING, OR LOWERING THE WHOLE MOTOR HAVE ANY RESULTS?"the 115 came off a 18 vhull the prop was close to the same size as the force i didnt check exact sizes.My first time working on a boat took it to 1 boat mec.for help with the throttle cables $500dollars and my reverse broke in the shifter. I have no more money to give away to crooks need help thanks.

[5150abf]

Ya, sounds like your engine is a bit high, drop it down a couple holes.

There is one set of holes in the boat and there should be several on the motor itself, go to the lowest ones and hope that does it.

That is called cavitation and is caused by the prop being to close to the water surface, it wants to push the water but there isn't enough to push so it blows out.

[poor man]

Have you ran this motor on the OTHER boat? at full throtle?? if so than skip this....

I had a motor that did just what you discribe, it was the prop. the ruber center was burned out it worked great till it heated up and WOT and it would rev up like putting it in netural. got a new prop and it was fine.....

[curtiscapk]

I agree sounds like spun prop to me..