[SBA]

Was hoping someone could tell me the maximum rpm's for a 1992 Evinrude 90hp. It's running at 4800 rpm's now, it seems to take a while to plane out. It has a three blade 14x19 pitch on it now. What would be a good size and brand for replacement? Thanks

[Dhadley]

You'll be looking for 5800 with an average load. 19s are not uncommon on V4s but it all depends on what hull and what the set up is like. My guess is that since you're off by 1000 rpm it's more than a simple prop change, assuming we're talking about an average type runabout or similar. First verify the tach and make sure the motor is running as it should. Once that's done we'll start looking at the actual set up.

[SBA]

Dhadley,
Reason I was thinking it might need a lower pitch prop, it just doesn't seem to have the power to get on plane. The boat is a 17' aluminum deep/wide Sylvan, has a 8hp kicker on back if that makes a difference for weight. The odd thing is when I go over another boats wake it seems to lose power, if you make sharp turns it sometimes picks up rpm's and takes off. If I have four people in the boat there is no way it will plane out, with two people, one has to be up front to plane. Sometimes it runs great, 38mph it's at 4800rpm's. I recently bought this boat so I don't know the history of it. What I have done so far is: new plugs and wires, had a spark test done and that was good. Compression is 125lbs in all cylinders. Drained built in gas take of old gas, changes fuel filter, rebuilt carbs. I also tried another gas tank and hose thinking that may be the problem. You mentioned to verify the tach, how is that done? Don't know what else to try, as it seems to be an intermittent problem. Had it to a certified marine mechanic and he's not sure what it could be. Would a fuel pump or CDI box cause this.

[tashasdaddy]

try a linc n sinc. also distribute the load properly in the boat. all the weight in the back it will not plane. you also may need to install a set of smart tabs, to help get the stern up, when taking off. do you have the motor trimmed all the way down, when getting out of the hole?

[kenmyfam]

At 4,800 RPM you are lugging the motor. Get the set up and loading sorted and see what happens. The extra resistance when crossing someone elses wake is knocking you off plane with the load you are carrying. If you had more RPM at this point it would drastically lessen the effect.

[SBA]

The only time The boat ran flawlessly was with the mechanic on board (of course) so problem was harder to diagnose. The only thing different when I had him with was i didn't have the kicker on the back. I wonder if just that extra weight made the difference that day. Next trip out I had the kicker on again and first wake I hit knocked it off plane. I always have the motor trimmed down when taking off. At WOT with motor trimmed up it will only achieve 4800rpm and 38mph. I'll have the link and sink done also to be sure everything is okay there. What type and pitch prop would be best for this setup. Thanks for all your advice.

[kenmyfam]

Work with a prop shop and get them to let you test some other props. Tell them the scenario and they will most likely make a good suggestion to begin with. Have the courtesy to buy the prop from them when you decide which one to go for.

[SBA]

Thanks, we have a great prop shop nearby. I think this has been an ongoing problem with the previous owner also, seems like everything I've tried or replaced trying to solve this had been tried before. I hope it's as easy as a prop change, I almost bought a CDI box yesterday thinking that was the problem. Told my eighty year old Father about the problem and everything I've tried, and he said I need a lower pitched prop. He bought a new boat years ago and didn't seem to have enough power, took it back to the dealer and other mechanics and could find nothing wrong, decided to buy a spare prop for emergency....put that on and never had a problem after that. I hope it's as easy as that.
Thanks again for all your help, I'll post after I try prop change.