If you are running a gates carbon belt, throw them away. They delaminate and explode under high power. I have not thrown a belt since I made the switch to the ultimate XS.
Next, it sounds like you have poor clutching. Belt slip causes excessive clutch heat and that leads to failure. If that is your issue, you need more clamping force on the belt. That requires new weights, stronger primary and secondary springs, and potentially a helix. What clutch gets the hottest? If it is the secondary, you need more force there. If it is the primary, you need more weight or a change in ramp profile. I wont clutch the sled. Call thunder products or someone familiar with your riding style. Ask thunder products about your helix. If the sled is tuned running stock clutching, you have to update the clutching for more power. If your clutches have been machined for over drive but the helix has not, you may be separating belts because the secondary sheeve is mechanically unable to reach an equivalent full shift to the primary.
Lastly, the sled is not limited to 85 or 88 at full load on a trail. I pull those track speeds under full load in chute. To do that takes about 350 hp. The thunder guys are into the 120 to 130s with smaller lug tracks on the trail. If it has stock gearing and helix, the secondary may be binding. I run factory clutches with a 911 cover, which eliminates tower flex in the factory viper clutch. Also, the thunder guys have said there is an issue with the factory winder clutch. The updates have weakened it compared to prior yamaha clutches.
