overpropped or maybe something more

[jheath6]

I am running a 1995 90hp force on a 18' sea pro 180 half to 3/4 full tank of gas and two adults and one child and small amount of gear. My prop is alum. 13 1/4 with 19 pitch. The boat seems to get up one plane ok but top speed is only around 26 mph using two different gps. The rpms are low like around 4200-4400 at wot. engine seems to sound ok and is not stumbling or anything. i know the recommended range is 5500 rpms for this motor. my question is do you think it is overpropped and if so what do you recommend to get the rpms in range, seems like 1100 rpms is hard to get just from changing pitch of the prop. could there be something else i am missing here.

 

[steelespike]

Re: overpropped or maybe something more

Yes you have more than prop selection problems.
Be sure the motor is in excellent tune, properly timed.Throttle plates opening all the way.Wouldn't hurt to do a compression check.Note each plugs location and condition.Be sure to ground the plug wires or crank it with the key off.
The antiventplate just above the prop should be visable at speed.
Raise the motor a hole or 2 at a time if necessary.
Its possible a 17" prop would be closer to what you need but it isn't going to solve your rpm problem.Be sure the bottom is clean and smooth.

 

[jheath6]

Re: overpropped or maybe something more

yea most of that i have done the only thing i have to do is check the timing and possibly check the height of the motor, i did forget to mention and this is probably a biggy. before I bought the boat the electric trim burnt out and he removed it now i have to set the trim in one place and keep it there till i get a new motor and get the trim back on. also the boat has bottom paint which i know does slow it some.

 

[BoomerSooner]

Re: overpropped or maybe something more

I would say your pitch is too high. 15 or 17 seems more reasonable. However, I would wait to see if your engine is at 100%. Then play with the prop. Check your engine height, that's free. You could also play manually with the trim and check your speed, but at most, I would say you would only pick up a few mph. I would start with the engine tuning first. It might be something you take to a mechanic, depending on your abilities of course.