Re: Building a 2004 Yeti DH-9 with 40cc Tanaka
I have the GEBE Tanaka 33 kit and I couldn't be happier. I started with a $440. (less 20% on sale) REI Metro "comfort" mountain bike with front shocks. It weighed 31 lbs stock. I installed the kit per instructions, added lights, a coil type lock, a tool kit with everything I need for a quick repair/flat fix, including an extra belt (not needed so far), and it weighs about 50lbs. The Tanaka 33 engine weighs about 3 pounds less though. I kept the stock 36 spoke wheel (wheels were fairly decent quality) and wire tied the spokes for added strength and it's doing great. With the stock gearing, it will do 30mph, and climb the hills around here without slowing too much, but you still need to pedal up to about 12mph to give the clutch a break. With trail gearing, I'm sure it would pull better, but I'd lose top speed.
As you say, it's best not to mess with the kit. If you mod the mounting and keep the 14.5 inch dimension correct, there should be no problem though. And you are right about these 33cc and 40cc kits being better for commuting and possibly easy trail rides. They won't turn your bike into a motorcycle.