Are you sure you got the right belt?

 

So your riding... you apply full throttle...
engine spools up fine.... no sputtering... no backfiring...
and you only get 25mph....

sitting still with the cover off... spool up the engine and the primary and secondary move as they need too...

have you tried to run it with the cover off so you can see if the belt achieves full deflection under load?

I'm no mechanic... and not suggesting you do anything unsafe... but if it where my wheeler, I would.... sounds like its the wrong belt though...

 

I will give it a try, but it does seem to lose power under the load of running. Which still makes me wonder if the valves are still out of adjustment.

 

Sounds like an excellent place to start!

 

Good luck and let us know what it turns out to be........

 

Thanks, Once on the road the belt will settle about half way down the front pulley. But once it gets to that position I lose power and some backfire. Still not over 25 MPH.

 

?? The belt on the front pulley should start very close to the bottom of the pulley. When you apply power the belt will raise (you said it settles) and the rear one should get closer to the middle of the pulley, or settle.
Is the backfire the engine hitting the rev limiter?
You said it was a new belt with a lot of slop.... are you sure its the right size belt?

 

I would definitely say belt.. Some ware in this post you said you had 2 inch of deflection? I read some ware that it should be some ware around 3/4" or their abouts. Look up a service manual for your machine and see what the specs are to be. The deflection should be close to the same for any AC machine.