Ok, I don't know what you guys use. But last year I bought a Exmark lazer Z and replaced the mule belt which runs from the engine to the deck. I bought the mower used and it did not have one. The problem that I have sometimes is I have to have the engine RPM up high to engage the blades or else the belt will jump off the idler pulley. This does not always happen. I don't know if it might be the belt maybe a bit too long. This belt part number mached up with an aftermarket because I could not see myself spending 55 bucks on a belt. I can get off the mower and look at it from behind and watch the pulley jump up and down a whole lot. I replaced the spring thinking that it might have lost tension, but it does the same thing. If I start it at a low RPM, the engine will lose RPM dramatically and the belt will jump. Any suggestions.