What did you change?
The Yerf's with the Howhit engine are geared pretty low already.
To be honest, I'm considering changing my gears to go up with the power mods I added. Plenty of low end TQ with the stock gearing as it is.
I do like the 12g sliders though.
This might help
http://buggymasters.com/forum/showthread.php?t=2670