I have a Steahly flywheel weight and it was my final mod to make the bike a true "woods" machine. I does exactly what it is suposed to do.....give better control and much more traction in the low to mid part of the power band and flatten out the hit just a little at the top end. Here are the other mods......PC Platinum II pipe and 296 silencer, moose reed valve spacer and VForce II (not III, II) reed valve. When I put the Vforce in (it has two settings, hard and soft I believe) I had it set on hard (stiff) and I found it gave the bike even more hit at the top. I changed it to soft and it made a world of difference at bottom and midrange. I dropped the needle one notch and went two sizes lower on the pilot also. The engine is perfect for the type of woods riding we do. I put a lighting coil in when I added the flywheel weight so I don't know if that added to the effect.
When I bought the bike two years ago, it was impossible to ride in the woods and fouled plugs EVERY ride. Finished the mods in June of 07 and haven't fouled a plug since.
I run Klotz oil at 50:1 with at least 91 octane gas.