quote Fisherman6:
Hmmmm, You say your 9.9 sits much lower in the water. Is your 9.9 a long shaft motor? Is it possible you have a 20″ transom on your boat? The “short shaft” 18s of this era have a shaft length of about 18″. Kind of a “mid length” shaft and would be too short for a long shaft transom. If that is the situation, cavitation could most definitely be your problem. Maybe just as the boat begins to plane it’s lifting the prop too close to the surface and it cavitation. The anti cavitation plate should be nearly even with the bottom of the boat when mounted to the transom. Say +/- about 1″.
Measure your boat’s transom. If it measures very close to 20″ from top to bottom and your 18hp doesn’t have the long shaft spacer in the tower, I think we found your problem. If your transomom measures close to 15″, then I suspect the prop is spun.
-Ben
Thank you very much Ben. I quickly measured 20.5" from the mounting plate to center of the bottom of the transom. the anti-cavitation plate sits about what looks like 3" maybe from the top?
what can i do to insure this is the case? if i set up a brum and run the engine without load can i figure it out?
Also, if this is the case, i am wondering what the tower spacer is, how its implemented and how i can find one? thanks again.