Low WOT Rpms around 4800 manual states 5250 on 98 force 120hp

[Bustedknuckle84]

I was getting more rpms, will weight affect the rpms?
What should i look for?

The motor sounds like its running pretty normal.

 

[pnwboat]

Re: Low WOT Rpms around 4800 manual states 5250 on 98 force 120hp

Weight will affect RPMs. Also propeller pitch. Water logged floatation foam under the deck can add several hundred pounds of weight to a boat and really slow it down.

 

[Bustedknuckle84]

Re: Low WOT Rpms around 4800 manual states 5250 on 98 force 120hp

prop has been the same, i have been carrying more gas which would equal more weight.
also i verified that the throttle plates (with motor off) open all the way up in WOT position.

 

[pnwboat]

Re: Low WOT Rpms around 4800 manual states 5250 on 98 force 120hp

How much more gas are you carrying? Gas doesn't weight as much as water. Anyways, I would suggest a compression check to verify you don't have a mechanical problem. If compression is in the neighborhood of 120LBS or higher, you should be good to go. Also replace the Fuel pump diaphragm if it hasn't been done recently. The diaphragm can get small pin holes or gets stiff and deformed so it doesn't work well. Make sure all of your vacuum hoses are in good shape and not cracked or leaking.

 

[Frank Acampora]

Re: Low WOT Rpms around 4800 manual states 5250 on 98 force 120hp

Reread the plate. There is a lot of confusion about RPM. The engine should be rated to run between 4500 and 5500 RPM at full throttle with the rated horsepower deveoped at 5250 RPM.

Generally, they like to run on the high side of the ratings but you are still within the range at 4800. If RPM has suddenly dropped or even graduallydropped, look as above, weight, and look at the bottom of the hull. Dirt, bottom paint condition, damage to the hull, worn propeller--any number of factors can cause loss of RPM, including a partially clogged filter , tank pick-up, quick-connects, etc.

 

[Bustedknuckle84]

Re: Low WOT Rpms around 4800 manual states 5250 on 98 force 120hp

Weight will affect RPMs. Water logged floatation foam under the deck can add several hundred pounds of weight to a boat and really slow it down.

how do i find this out or drain the water logged floatation foam out?
i do have the boat parked with the bow higher then stern and verified that water does drain out the bottom. not sure if this helps.

 

[Bustedknuckle84]

Re: Low WOT Rpms around 4800 manual states 5250 on 98 force 120hp

gas-about 3/4 to full now, i did a comp test about 6 months ago but ill do another one, fuel pump has less then 10 hours on it. i would like to tackle the weight issue, thanks so much for the info guys.
when i didnt have the problem i think i was carrying about a half tank or less.

 

[Bustedknuckle84]

Re: Low WOT Rpms around 4800 manual states 5250 on 98 force 120hp

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