Formula III,
If I were you I would start to narrow down my options. Start with the easy things first. Take off the exhaust pipe, check for mouse nests ect. Use an air hose and make sure air blows through nicely. Also check the exhaust manifold for same prob, and do the same. With the manifold off you can check for mouse nests in the cylinder as well. "I have seen this before in sleds that have sat a while" Sometimes mice build nests in the cylinder itself. If nothing, put it all back on and do the same to the carbs. If nothing there check your plugs one at at time. If still not the problem, then I would check your clutch. Check your rollers and weights for flat spots. If they are worn flat this will cause them to stick when they get to that point and then stall out causing your sled to not move until you build up enough power to force the weights beyound that point, so it depends on where the flat spots are if there are any at all. If that dont work check to make sure the clutch compresses smoothly. Run the motor and give it a little gas and see how easy the clutch engages, just needs to move a little. If it seems to work fine, play with the amount of throttle and see if you can see it grab the belt, if it grabs the belt but then wont move I would say its a drive shaft bearing. If it wont even grab your belt before it boggs and stuff then I would say its your carbs or clutch.
Finally If none of that works I would pull your suspension out and then take your track & drive shaft off and check your drive shaft bearing. It could be shot and causing you not to have any power because you cant turn the bearing, and then every once in a while it will give and move then lock up again.
These are all things you should be able to do on your own.
If you need further help just ask. Those 500 motors are like tanks, they're awsome!
