Here is some tuning for those in need.

This is general information on the Mikuni carbs found on the Chinese Import Pit Bikes. Most the Carbs use Mikuni (RS and HS) Main Jets and Pilot Jets I believe a 15 pilot comes in them from the Factory go up to a 17.5 Pilots range from (15, 17.5, 20, 22.5 & 25) you will never need any bigger Mains range from 60-100 and from 105-200 in increments of 2.5 Try a 17.5 pilot 100 main and turn the air screw in till its 1 turn.


1) PLUG READING: You need to run the bike in as tall of a gear as you can and then kill the engine with
the throttle wide open. Don't idle the engine, now remove the spark plug and look at the INSULATOR, the
white porcelain part. As a rule it should look like coffee and cream (TAN). If it’s Dark brown or sooty black your motor is running RICH. A gray ashy or white reading means its running LEAN. A plug reading only gives you an overall view of how the motor is running.
Do this with a new plug and make sure your bike is warm first.

2) THE MAIN JET: The carbs main jet affects how the carb works from half to full throttle. After you have
made your test run with the stock jetting, install a main jet that is two sizes richer it will have a higher number than you removed. Do your test run again & pay attention to how the bike feels. If your bike is reluctant to REV out like before, then you are too rich. Now go back and install the next smaller main jet keep doing this until you feel a noticeable improvement in power once you have the main jet set go on to your pilot jet.

3) PILOT JET: The pilot jet has the greatest ifluence from idle to 1/4 throttle to test the pilot jet that is two sizes richer (just like the main jet) now go out and test it pay attention to how it feels when you pull out of the slow turns. If your bike is too rich it will feel sluggish and unresponsive until you are past 1/4 throttle a perfectly tuned pilot jet will help your bike accelerate off the line and out of corners. Repeat this test until you get one that feels the best.

4) THE AIR SCREW: How to adjust it, with a warm engine bring the bike up to a steady throttle setting
(about 1800 RPM's) get a friend to hold the throttle steady......Once the engine is running at fast idle.
Turn the air screw in clockwise until the engine rpm drops. Then slowly turn the air screw out until engine rpms pickup.....Stop turning the air screw once the RPM's reaches its peak. Peak rpm is when the engine runs it's cleanest and fastest. The most common air screw adjustment is from 1/2 a turn to 2 turns out. If your air screw is more than 2 turns out it is a warning that you should switch to the next LEANEST PILOT JET....If the engine has peaked before turning a 1/2 turn out. Then switch to the next largest Pilot jet.....

5) NEEDLE JET: Your carbs needle affects throttle settings from 1/4 to 3/4 turns lucky you don't have to replace the needle to adjust. Start out with the clip in the middle setting make a couple of runs, then change the clip down two positions. This is the quickest and fastest improvement you can make to the
bikes jetting. Don't be afraid to move the clip up...LEANER or down...RICHER. You spend most of your
time riding in this range. Try all clip positions on the needle see what runs the best.... If you find your clip position at the very top or bottom. Then you need to go back to your main jet and pilot jet and make a different setting... When all is done your clip should be in one of the three middle notches.