Barnett clutch springs ended the slippage problems I had in both my 175 motors (I use OEM plates, the Barnett plates slipped a bit from day one). If your clutch is just starting to slip, you may get away with just replacing the springs and leaving the clutch pack in place. Mine are quite a bit stiffer than stock, but lever pull isn't a problem for me.
Application Guide: (the '81 CR450R uses 501-40-06011 springs):
http://www.barnettclutches.com/products ... tch_cc=450Here's where I got mine from:
http://www.phatperformanceparts.com/Pro ... TS&CartID=Ray