carb modding
1) main jet control the maximum amount off fuel available to the engine (part#16) factory 120 upgrade to 140 (I found my at my local motorcycle dealer , look for small mikuni main jet or take the old one with you)
2)needle shine control the fuel at mid range move the washer (part# 9)from the top of the E-ring (part# 10) to under the e-ring to improve the mid range
3) Pilot jet (part#26) control the fuel from idle to about 1/8 of Throttle factory set under 2 turns from the close position new set 2.5 to 3 turns, you may need to remove the plug (part#26A) to gain access, improve idle and reduce the fluctuation be twin col and hot idle
4) Upgrade air filter (I modify the factory filter see second picture)
http://www.gz250bike.com/forum/attac...9&d=1408145033
http://www.gz250bike.com/forum/attac...0&d=1408147180