Engine seems to be slipping at high speed

[unklrick]

I have a 24' pontoon with a 1978 115 Johnson on it. It does great at low RPM but when trying to speed up it seems as though something is slipping, the engines revs and the toon slows down. I'm a newby with toons and would be thankful for some help with this problem.

Thank you,
unklrick

 

[laniertoon08]

Re: Engine seems to be slipping at high speed

I have a similar problem w/ my 24'toon and johnson 88 spl, 4200 rpms runs good but not fast.
wot seems to have very little increase in speed maybe my prop diameter is too small...

 

[Big Bubba]

Re: Engine seems to be slipping at high speed

unklrick,
Check to see if your prop is slipping on the hub. You can draw a line across the prop hub to the inner hub to see if it is slipping or not once you take it out of the water again.

 

[EGlideRider]

Re: Engine seems to be slipping at high speed

It is likely a ventilation problem. Try putting most of your load toward the stern and try it.
You do have a long shaft motor?

And Lanier, pontoon speed vs. RPM's is a very nonlinear curve so little speed increase will normally be observed above about 4500 RPM's with a properly proped(sp?) boat.

 

[unklrick]

Re: Engine seems to be slipping at high speed

it will run along fine until I start around 2500 to 3000 and then it doesn't seem to jump out of gear but seems to slip, I can throttle back down and it does fine again. I tried easing the throttle up slowly and it seemed to do a little better but would still do the same thing, like a clutch slipping on a bike.

Thank you again for the help,
unklrick

 

[EGlideRider]

Re: Engine seems to be slipping at high speed

As mentioned by big bubba, it could be the hub slipping and as he indicated, that is an easy check. Otherwise, it is probably ventilation that will be solved only by getting the prop lower in the water; either dropping the motor or shifting some weight to the stern.

 

[unklrick]

Re: Engine seems to be slipping at high speed

thank you very much, I will check that this weekend and post the result's

thank's so much,
unklrick

 

[lncoop]

Re: Engine seems to be slipping at high speed

Sure sounds like a spun hub to me.

 

[Merc_115]

Re: Engine seems to be slipping at high speed

i have a 25 ft crestll same thing @ wot i hear the motor rev lil higher here n there

 

[lncoop]

Re: Engine seems to be slipping at high speed

i have a 25 ft crestll same thing @ wot i hear the motor rev lil higher here n there

That's not the same thing. Revving "lil higher here n there" could very likely just be occasional prop ventilation. A spun hub results in a complete loss of thrust at high RPMs because the prop is just free-spinning.

 

[Merc_115]

Re: Engine seems to be slipping at high speed

yea the guy docked next to me went through that lost thrust high end could only idle back, was spun hub, not tryin to rob thread just seen post of similar things im exp

 

[phattyd]

Re: Engine seems to be slipping at high speed

My bet is ventilation. I just took delivery of a 22ft 2-toon with a 150hp Yamaha and had major ventilation issues that match the description unklrick posted almost exactly, lowered the motor 2 holes to the next to last position (Putting motor lowest in the water) and resolved alot of it, then moved the motor down again to the last hole and almost all the ventilation issues are gone. I still need to have the people on board sit as far back as possible when WOT (45mph)