Fm165 60 hp motor high rpms

**dester223** · 12-08-2012, 07:10 PM

I bought a used 2007 fm165 60 hp 4stroke. Anywho. First day on the water the rpms easily hit over 7000 and barely did 20 mph. Went to midwest prop and he informed me an 11 pitch prop was put on. Bought a 14 pitch prop. Rpms dropped but its still hitting over 7000 rpms. Max speed hit near 30 mph.

Previous owner hit and broke the original prop. Is there any other part in there that can cause the high rpms? Searched online and most run a 13-14 pitch prop on the same boat. Midwest prop said a 15 is as big as it gets? Not sure if another prop change will fix my issue????

**Cray** · 12-08-2012, 07:25 PM

Stainless or aluminum prop? Check motor height on transom. Should be all the way down if alum. Up one bolt hole if stainless. Where are you running trim? To high on transom or trimmed out to far both could cause this problem. You have a tremendous amount of prop slip for some reason.

**dester223** · 12-08-2012, 07:35 PM

Trimmed all the way down. I know trimming up will increase some rpms to let it pick up some speed. I will check transom holes to see how far it's mounted

**dester223** · 12-08-2012, 07:35 PM

Oh yes. Alum prop

**"G"** · 12-09-2012, 09:48 AM

Sounds like your using a prop hub thats spun out on ya

**Barnacle Bill** · 12-09-2012, 11:09 AM

With the motor down in running position the anti-cavitation plate should be even with the bottom of the boat. Also its possible your tach is not set right and giving you wrong info. What brand motor is it?

**wilbur** · 12-09-2012, 05:16 PM

Check the tach. 7000 is really high for a 4 stroke.

**Archerguy1** · 12-09-2012, 05:22 PM

I would see if your tach is set properly, I have seen tachs go bad, or the rectifier, that sends the signal to the tach cause the problem

**dester223** · 12-09-2012, 08:38 PM

It's a mercury. I suppose I can get a timing light to check and verify the rpms.

Also how do you check if the prop hub? The splines where the prop goes in looks good. I am ok with car stuff but boat stuff I am still learning.

**Archerguy1** · 12-09-2012, 09:16 PM

If the hub is the Flow torque type, with a plastice /brass insert then it's easy to check, if the hub has a brass/splined insert with rubber around it , the only way to truely check it is a prop repair shop......but if this motor/boat set up gets on plane and runs on plane then you can just about rule out the hub, it would slip/spin at the point of most torque and thats right as the boat starts up on plane. If you are up on plane and running I would look into the prop first, pitch and diameter, make sure it's right for your set up, again a good prop shop, or merc dealer may be albe to steer you in the right direction before you go moving the motor or throwing parts on it. And going back and reading your first post I think a 14 pitch may be a bit on the small side, 16 ft boat with a 60 should be able to sling a 15 or 17 pitch in a 11 - 12.5 diameter.

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