Pontoon Boat & Deck Boat Forum

Hi All!!! I hope all of you are staying out on the water as mush as possible!!!

I have a couple questions- I do not think related, but I will post together just in case-

Boat= 24' Grumman with Evenrude "88" on it- Both late 80's

1st - I have had a problem with cavitation since day one, but not super bad. Just when going full steam and trying to make a sharp turn... The last few trips it has got real bad. If I am going any where near top speed, as soon as I start turning to the right, it cavitate's, and bogs down immediately...After doing this several times yesterday, it lead me to the next problem...

The engine started running real rough.. missing real bad. Kicking in and about. Had to run about 1/3 throttle to get her out of the lake.

Like I said, probably two unrelated issues, but It all started happening yesterday-

any ideas where to start???

Regards, Jason

I'm a newbie as well so others can chime in with more experience but the cavitation issue you describe sure sounds like "prop blowout". Basically in a turn the prop runs out of water to churn because of the wake. It's a problem with pontoons because of the hull shape. I have seen it is my boat. My solution has been to trim the motor down going into a turn and then trim back up coming out of the turn. Try searching this forum for the words prop blowout and you can find some other advice on the subject.

The rough running engine could be from water in the gas; a real problem for boats due to the infrequent usage and ethanol gasoline's propensity to sweat. Normally this would happen when the tank is nearing empty. I'd try using some "dry gas" or gas treatment to see if you can fix the issue.

Thanks Flossy- The prop blow out sounds exactly like what it is doing- I have played with the trim quite a bit to see if I could make it better, but no luck so far. The weird thing is that it has all of the sudden got way worse than it has ever been. (at least the season and a half I have been running it ha ha) It could have been just the lake conditions- It was pretty rough out there yesterday. I will keep working on that...

On the engine. Water in the gas, or bad gas, was my first thought. There is a small gas station that I always get gas from. They advertise "Ethanol Free"- but still could have some issues. The trip before, I was filling up with 5 gallon cans. They did get rained on.I did not think any rain made it in, but you never know, they might have gotten a little water in them... I had about 4 gallons of that gas left in the boat, then I put in 15 gallons of the fresh, ethanol free, gas before we left yesterday. ran good, except for the "blow out" problem- probably an hour 1 1/2 run time is when it started acting crazy-

Get your... ahem... larger passengers to sit more towards the rear.

Or try a 4 blade prop designed for a pontoon. They claim to hold better in turns.

Thanks trucky- Never heard of 4 blade prop for pontoons.. I will start looking into that now!!!

Mercury makes the Nemesis and the Spitfire. They're both the same prop but one comes with the hub.

http://www.qsprops.com/aluminum/nemesis/

drop the motor down a hole

I've got a Johnson 88 SPL...
on a 21' Sun Tracker...
Had the same cavitation issues...
I dropped the motor down as far as possible...
use a 13" Evinrude Hydrus Prop ...
no issues since.