What could this problem be -

[CLC]

I own a 1996 GTS Bombbardier and the craft idles fantastically but when I push the gas to go....it revs up but does not get up to speed. I have made sure that there is nothing in the propulsion and in the grate on the bottom of the craft. Any ideas...

 

[Dr Honda]

either very bad cavatation or the splines are torn out of the PTO.

For the PTO... grab the driveshaft and give it a twist. If it moves... then you may need a new PTO or drive shaft.

For the cavatation... the only thing that can cause that bad of cavatation is a bad carbon ring. (driveshaft seal) I would replace all of it. You will need a new boot, carbon ring, stainless ring, o-rings, and a c-clip. Do a search, there are threads on how to change it.

While you are in there... check the impeller and the wear ring.

 

[Bills86e]

If you remove the grey drive cover, you could use a majic marker and put an alignment mark on the shaft & PTO. Later, see if still aligned.
A wear ring measurement is needed. Bill