A flywheel costs about $20. If you don't have a pair of digital calipers, that's where I would spend my money. The MTX4R clutch is a very predictable clutch, when it is set up correctly. How is the clutch performing for you at the track?
"Yellow Jacket" Mugen MTX-6, Picco Torque
TeamNITRO RC Club, Lynwood, Illinois