1998 force 40hp help

[james goddard]

When I power up my motor to get on plane the motor seems to slip ( rpm,s go up but the boat doesnt go any faster). It only seems to happen when it,s cold. It Just started doing this about a month ago. It doesnt do it every time I go out. I,ll back of the throttle then throttle up again and then it will be ok the rest of the day.Yesterday I had to back off throttle twice before it stopped doing it.Anyone ever had this problem? ,,,Thanks Scott

 

[Dan J.]

Check for a spun hub in your prop. With key out and kill switch off (dead motor) put throttle in forward and walk to rear of boat. Grasp prop with a towelled hand for safety and try to turn prop. If it moves without cycling your pistons, your hub is probably spun and needs a new one. (Either pressed in or Flo-Torque depending on your prop.) With the basic info given, that's where I'd start. Good luck!

 

[james goddard]

I just put a new prop on a few weeks ago. It did the same thing with the old prop.

 

[Dan J.]

Without the hub slipping then it sounds like you're blowing out. (High RPM's with reduced thrust - cavitating) What prop(s) are you using on what hull? (Brand/pitch/style) Jackplate, and if so, pad to shaft measurement?

 

[james goddard]

I was using 15 pitch that came on the boat. Talked to BOB b. and he got me 4 blade merc prop with a 12 pitch works great.I only have this problem (so far)the first time I power up when I go out.After that I can shut the motor for a few hours start it back up and it works fine.It did the same thing with the old prop. The boat is 1997 tracker pro 18.

 

[Dan J.]

Hopefully when Bob gets a chance he'll poke his head in on this. The sporadic nature makes this a head scratcher for sure. Good luck!

 

[james goddard]

Yeah I can,t figure it out its not like its slipping out of gear.I don,t know what it could be....Thanks for taken the time to help me out....

 

[Bob Bourget2]

Something is not making sense. The crankshaft is splined to the driveshaft, the driveshaft is splined to the pinion gear, and the forward-pinion-reverse gear are meshed constantly, with the only "clutch" being the slide bewtween the two gears over the prop shaft. It will make a terrible ratcheting noise if it "jumps". It is connected to the prop, and the new prop has a "plastic" hub....one that is either good or bad. It sounds as though {since it happened with two different props}, that we might have some unwanted ventilation going on...the question is why? Other variables....tach going awry, giving the operator false rpm info, electrical glitch causing the tach to be jumpy....etc.......????

 

[james goddard]

What could cause unwanted ventilation ? I dont hear any grinding just the engine rev and the boat doen,t pull any harder.Once I back off the throttle and it stops doing it ,she runs fine all day. Its only the first time I try to get on plane.

 

[Bob Bourget2]

Are you trimmed down fully?

 

[james goddard]

Not sure if I was trimmed all the way down or not when this happens.But I,ll make sure I am for now on and we,ll see what happens. Was out today didnt have any problems.