I would like to share these few tips/tricks/bits of information that I have learned with my gasbike adventures so far. I'm sure some of these ideas or at least a variant of them have already been mentioned, but this is just what I've done and it flat out works.
Some of the clutch levers in the kits we've seen from our builds are very noisy. When you pull the lever to release the locking pin and engage the clutch, the pin would always make a loud, annoying metallic "TINK!!" sound... Well I grabbed my box of orings I had laying around and stuck the smallest one I had on there, doubled up so it would stay. The metallic noise is GONE! Nearly 100% silent now so that's good!
I know there is a lot of talk on modifiyng or outright replacing the stock air filter assembly. What I did to mine was drill a very large hole in the cover itself so that the carb can easily and efficiently induct all the air it needs and it still passes through the filter foam. I can actually feel the air flowing by my fingers when I put them there while the engine is running.
This one is more cosmetic, I just took a utility knife and trimmed off all the ugly extraneous plastic of the filter housing that would overhang the carb body. Looks much cleaner I think.
When I first built this 29er, I used the regular "C" shaped front mount strap with some longer bolts. No matter what I did here, the bolts ALWAYS broke. I had to use EZ-outs TWICE to extract the remains of two bolts that had broken off flush in the threaded hole itself. Then I noticed, wait a minute, these kits also have this other flat strap mount that bolts to the engine, and then is held to the bike frame by a ubolt. Not a big or complicated thing but still something to note. If you're motorizing a bike with a larger than normal down tube as is the case with this one, you definitely want to use this style mount, or even better perhaps, fabricate your own. Since I swapped to this style, no more broken bolts.
Which brings me to my final tip. I used to use loctite and lockwashers everywhere, but for some reason I still had fasteners vibrating loose!!! My solution? Again nothing new or groundbreaking but it works: double nut EVERYTHING. Everything you have the room for it I reccommend doubling up the nuts.