Would take it back to the place that put the motor together and let them have a look. Is it not covered under warranty? Sounds like something wasn't right from the get go.
There is a rubber dampner that has protrusion on it to keep it in position when the metal band is tight. Seeing that it was loose and rotated it may have broken the rubber at this point. Check to make sure that it is still intact and ckeck to make sure that the metal band clamp stays tight. Doo...
The secondary clutch for this sled should have aprox 15lbs of sring preload.
You should not easily be able to pull the two sheaves apart. If this is happening then there will not be enough side pressure on the belt causing it to slip and take out the belt.
I'm surprised that nobody has mentioned anything about the new DI 600 e-tec 2-stroke. Amazing fuel and oil economy and first pull start no matter the temp. Just something to think about.
The top line on the tank is a vent line and can be easily replaced. Try cleaning the carbs and replacing the fuel filter. Also check the fuel tank for water or dirt. Hope this helps.