RPM's at WOT 92 90HP Force

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dcar00

Seaman Apprentice
Joined
Apr 11, 2004
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44
I have a 92 90HP Force SN#908F92C. When i hvae it in neutral and push the throttle all the way up the RPM tops out at 3000. When I am out on the water and have the throttle wide open the RPMS are 4800. <br /><br />is this normal? If not, what might be the problem.<br /><br />Is 4800 RPM normal at WOT for this motor?<br /><br />I have a 24ft pontoon boat. <br /><br />Thanks for any help you can give.
 
12Footer

12Footer

Fleet Admiral
Joined
Mar 25, 2001
Messages
8,217
Re: RPM's at WOT 92 90HP Force

That sure don't make sense to me. It should be the other way around (less RPM under load).<br />But 4200-5000 is normal, depending on prop pitch.
 
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dcar00

Seaman Apprentice
Joined
Apr 11, 2004
Messages
44
Re: RPM's at WOT 92 90HP Force

12 Footer,<br /><br />Thanks for the reply. Do you think I have any chance of ruining my engine by running while this is going on?<br /><br />Could it be bad compression on a cylinder or becasue it runs fine on the water that can't be the case?<br /><br />dcar00
 
12Footer

12Footer

Fleet Admiral
Joined
Mar 25, 2001
Messages
8,217
Re: RPM's at WOT 92 90HP Force

If you are using a pressurised water supply (garden hose hooked to earmuffs) to run in the driveway, and have lower RPMs here than you do one the water, I would highly suspect a blown head or exaust port plate gasket. A compression test will probably reveal that, but to be sure, look for one or two "cleaner than normal", or cleaner than the other, plugs.<br />That's the only thing I can figure would cause this diferent result in and out of water.<br />A motor in gear, under load, will produce less RPM than it will in neutral, no matter what....Unless it's eating pressurized water.
 
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dcar00

Seaman Apprentice
Joined
Apr 11, 2004
Messages
44
Re: RPM's at WOT 92 90HP Force

12footer,<br /><br />I may have confused you. I have the boat in the water all the time. changed the plugs this year and they all looked the same. fairly black not clean at all. <br /><br />This is weird. I wonder if it could be related to the throttle linkage when it engages into neutral.<br /><br />Where is the best place to get a compression gauge?<br /><br />Thanks<br />dcar
 
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