I was a long time 125 woods rider. Just loved the light weight. Ride a 250 now, just because I got tired of doing all those top-ends. On Suzuki's and Kawasaki's you can add low-end by shimming out the expansion chamber... meaning, simply adding more head-pipe length. (2-3-or 4 additional washers/gaskets). You'de be suprised how much of a low-end improvement you can get this way. I think Yamaha's have a different pipe flange, but you can probably work around it somehow. Carbon Tech's "low-end" reeds work well too. I even advance the ignition just slightly. And shaving off the base of the cylinder will help too, if you want to go that far, but you have to watch-out for the added compression... I never liked any form of additional flywheel on a 125, just too hard to get on the pipe. I've heard that the Yamaha's have decent low-end though. If I were you, I'd start with about an 8 oz. weight and have a machinist shave it down if it proves to bog you down. 125's are so fun, but you pay a price on nasty uphills... get on the gas, get aggresive, stand up, and be prepared to chase the rear-end around. But,... in flat, tight woods or on down hills, you will ROCK on your tiddler! Have fun.