I have a 1995 XLT SP 600. Ijust cleaned out carbs and synched them, all new plugs, gas, fuel lines. The problem is when idling idle fluctuates. When you punch it the sled bogs down and backfires then it screams. Sometimes it doesnt do that at all. I put it up on a stand with the hood open and i think the popping is coming from the clutch side cylinder. All the plugs look fine and compression is 123 on all three cylinders. Could this be a blown crank seal. Please help me out. I am stumped.