Pontoon Boat & Deck Boat Forum

Since all my parts finally came in, and I got them installed... to the lake I went!!

Had a great day, engine ran great with the newly rebuilt carbs! I'm running SeaFoam through the gas tank to just clear out any left over gunk now that the carbs aren't restricted.

I am getting what I'm assuming is cavitation...a little direction would be appreciated. I can get her up to full throttle or crusing speed and be running great, but then the RPM's will go up about 200-300 and I'll lose 2-3mph GPS. I'm still moving pretty well. I do think my engine's running a bit low as I can't see the cavitation plate at all while underway, would this cause it? Think a prop swap could fix?

All in all, I'm happy with the way it's running

I had the exact same issue at WOT. Motor at the proper height and still the cavitation/ventilation. Problem solved with a Doel-Fin.

oh, forgot to mention that I have to drop it pretty much to idle before I can get out of the cavitation/ventillation

Might want to check the condition of your prop hub.

Prop guard fixed it for me and gave me a lot more low speed control

trktrd wrote:Might want to check the condition of your prop hub.

Agreed.
You may be spinning the hub, and it doesn't lock back up, or fall back into a groove until there is almost no pressure on it, hence hooking back up at idle.

Ventilation comes when your prop is out of the water too much. It grabs air.

Chances are you need to trim your lower unit down a little when it does that. Or, your motor needs to drop a notch.

My boat runs great and I run it trimmed it up to about 3/4 on the trim gauge. It accelerates great from a start @ 3/4 trim. But when I slow down and take a tight turn, it ventilates just a little. That's exactly how I want it.

If I was going to pull a tuber, I'd drop the engine down some and wouldn't experience any ventilation. My motor is in the second notch--3/4" off the lowest it will go on the transom.

If your engine height is right, you can still get ventilation. Sometimes having a correct prop makes the difference, however.

I went ahead and switched props/hubs. I think the motor might actually be too low, so not worried about being too high. We'll see how it does next time out