We took off the stock Tecumseh 6.5hp motor and replaced it with a new Predator 6.5hp motor.
Tecumseh
that 6.5 is more like 4.5.
We're trying to get it to run as stock as possible. All we did was swap the motor. Should be the same power?
A tired worn out engine, versus new... there's the fly in your soup. The Tecumseh "6.5" is optimistically over rated to say the least.
The belts are cheap (amazon), the belt pulleys are rusty and filthy. And I'm sure we've got some extra resistance somewhere.
Rusty crusty sheaves won't cause the violent shuddering, but they will eat up belts. Even good belts won't last.
I'll see if cleaning and lubricating (conservatively) helps engage the belt smoother. And we'll buy some better belts next time.
If you're going to try salvaging the old TC, I recomend you get some fine grit paper (800 will do) and some paint stir sticks. Wrap the paper around and tack it in place, run the engine at idle without a belt and use the stick to take the surface down smooth and shiny again.
After that put the kart on jackstands, pop a junk belt on it, turn the rpm up on the idle screw until the secondary turns steady but isn't sucking the belt down and repeat the sanding process by carefully reaching into the sheave between the top and bottom belt spans with the sanding sticks.
You won't be able to do the rear driven sheave this way, but 3 surfaces out if 4 this way saves a lot of time and energy.
Actually You could do the rear sheave on the secondary this way with the belt off if some volunteers spin the rear tires manually for you while you sand it though.
Unless it's a genuine Comet 30 unit, it seems to me it's in your karts best interest to just buy a genuine comet belt and a new TC instead of continuing to fuss with it. The sanding will only save it if the sheaves are surface rusted because any galling or rust pitting is still going to eat up a belt no matter how shiny you get it and you don't want to take off anything more than absolutely necessary forbthe sake of weakening the sheaves or eroding them past their tolerance for grabbing the belt efficiently.
It occurred to me that another thing that can cause the violent shudder is if the driven spring is weak or adjusted too soft, with all the rust mentioned I'm betting gone soft. What ends up happening is the primary yanks the belt through the secondary but without enough spring resistance it basically tried to take the belt all the way to the spindle which won't move the kart from a dead stop IF it bites... it still goes back to my first comment regarding belt slippage in any case.
The ONE AND ONLY thing I've ever had make a TC shudder like the whole machine was comming apart is the belt slipping. No IF's, And's, but's, or maybe's about it what-so-ever
