97 Force 120 Max RPM

[stssa]

Max rpm shows 5250 but my force 120 does about 4800rpm. Do you think Carbs need a rebuild or re adjust the needles maybe?

 

[pnwboat]

Re: 97 Force 120 Max RPM

If the motor is running smooth and starts up OK, I wouldn't mess with the carbs. If the motor is running fine other than maximum RPM's being down 450 from maximum, then that's probably all she's got. There are many variables that affect maximum RPM other than the motor itself.

1. Prop pitch. Going from a higher pitch prop to a lower pitch will increase max RPM's, give you a better hole shot but will decrease top end speed.

2. Weight of the boat and design of hull.

3. Motor trim at max RPM. If the motor is trimmed all the way down, it forces the bow down creating more drag and more load on the engine reducing RPM's. Trimming up allows the bow to rise and reduce the drag and load allowing the motor to reach higher RPM's and also increase top end speed.

 

[stssa]

Re: 97 Force 120 Max RPM

Thanks for the input I was reading about it. This is my first boat. I used to own jet skis and if they dont reach to top rpm it usually meant a carb issue. I never thought about the trim issue. Yesterdaywas my first time out with it. I was crusing with trim all the way down so that was probably it. I will take it out again today, I will play around with the trim a little more and see if I can get more rpm and maybe a little more speed out of it. Its mounted on a 97 Maxum 1900xr bowrider. and

 

[Frank Acampora]

Re: 97 Force 120 Max RPM

Re-read the plate. It should say operating range 4500-5500 RPM, 120 HP at 5250 RPM. At 4800 you are in the correct operating range so the engine would appear to be running well, but if you want to gain a few more RPM, then a prop change is the way to go. Drop down 2 pitches to gain 400 RPM--However, with the lower pitched prop, speed may remain the same or even drop a couple of MPH.