While jetting carburetors, place a piece of tape on the throttle housing. Place another piece of tape on the throttle grip and draw a line (while the throttle is at idle) straight across from one piece of tape to the other. When these two lines are lined up, the engine will be idling. Now open the throttle to full throttle and draw another line directly across from it on the throttle housing. At this point, there should be two lines on the throttle housing, and one on the throttle grip. Now find the half-way point between both of the lines on the throttle housing. Make a mark and this will show when the throttle is at half throttle. Divide the spaces up even again until idle, 1/4, 1/2, 3/4, and full throttle positions are known. These lines will be used to quickly find the exact throttle opening while jetting.
Clean the air filter and warm the bike up. Accelerate through the gears until the throttle is at full throttle (a slight uphill is the best place for this). After a few seconds of full throttle running, quickly pull in the clutch and stop the engine (Do not allow the engine to idle or coast to a stop). Remove the spark plug and look at its color. It should be a light tan color (for more info on reading spark plugs click here). If it's white, the air/fuel mixture is too lean and a bigger main jet will have to be installed. If it's black or dark brown, the air/fuel mixture is too rich and a smaller main jet will have to be installed. While changing jets, change them one size at a time, test run after each change, and look at the plug color after each run.
After the main jet has been set, run the bike at half throttle and check the plug color. If it's white, lower the clip on the jet needle to richen the air/fuel mixture. If it's dark brown or black, raise the clip to lean the air/fuel mixture.
The pilot circuit can be adjusted while the bike is idling and then test run. If the engine is running poorly just off of idle, the pilot jet screw can be turned in or out to change the air-fuel mixture. If the screw is in the back of the carburetor, screwing it out will lean the mixture while screwing it in will richen it. If the adjustment screw is in the front of the carburetor, it will be the opposite. If turning the screw between one and two and a half doesn't have any affect, the pilot jet will have to be replaced with either a larger or smaller one. While adjusting the pilot screw, turn it 1/4 turn at a time and test run the bike between adjustments. Adjust the pilot circuit until the motorcycle runs cleanly off of idle with no hesitations or bogs.
Altitude, Humidy, and Air Temperature