I started the build with a brand new 26" Motobecane 400HT.The bikes parts spec includes a Longer travel Suntour 100mm fork with adjustable pre-load, competitive race quality 24 Speed Shimano Alivio parts and powerful Tektro disc brakes. Also has double wall rims and sealedsealed bearings. I went through JNMotors.com and got there 66/80cc sms black engine kit. This is a great engine they go through the engine and change the bearings and out a better intake setup on it then give a 3 month warranty with it. I then purchased the 2-stroke HD shifter kit from sickbikeparts.com. this bike turned out beautiful and rides amazing. My last bike was a29er from Wal-Mart and picked up a motor kit locally and after that got stolen I wanted to do this build right. The break in is now complete and I opened up the baffle inside the stock exhaust and drilled one more whole in the cap and put it back together. I then customized the air filter housing to allow more air flow. I then opened up the intake port on the outside of the cylinder head and the intake manifold. I noticed a huge improvement in power. I need some advice on tunning issues. The bike came with the nt speed carburetor and the bike is running lean on the top end and I'm having to run it rich on low to mid because I don't have the main jet. I'm thinking of getting a expansion chamber exhaust and the upgraded to the ufo air filter. Are there any better carburetor out there or is thete somewhere i can get a main jet kit? And is it worth spending the money on the new exhaust, air filter, and carburetor? Any advice would greatly be appreciated.