Jetting a carburetor is more of a science than an art. When people think of jetting a carb many do it by the seat of the pants method but that does not yield very good results.

In the end the jetting of a carburetor is to produce results that will provide a nice tan color to your spark plug at all throttle settings. However a carburetor has many components that contribute to different throttle settings in proportions from 0-100%. So with this being the case knowing what jets contribute to what throttle settings will give you the ability to dial in your jetting. To know more about what jets affect what throttle settings read this as it explains all the different areas of jetting in a carburetor and for the most part is the same for all carburetors.

Now since you know WHAT jets to adjust at what throttle range you should in theory be using a dynomometer to scientifically read your fuel/air mixtures at the exhaust at different throttle settings. But we all know that not everyone has a $30,000 dyno in their tool box. So what to do? Well a dyno is nothing more than a stationary load on the motorcycle that can host measuring tools. However a spark plug will tell you if your mixture is rich or lean. Click here to see how.

Now since you know what to adjust and have a method of knowing which way to adjust you need to know a way to control which jets are contributing the maximum percentage in a given throttle setting. To do this you can take a piece of masking tape around your handle bar or switch assembly on the throttle side. Then put a push pin or sewing pin in the outside diameter of your throttle grip flange. make a mark on the tape with the throttle closed. Then make on with the throttle open all the way. Divide that range of 0-Full into 1/8 increments that you can view while riding.

Now go get your spark plug wrench, an a set of gloves. You are about to do a throttle chop, (of course you need to do this in a closed course environment like an abandon runway, or your nearest drag strip). The easiest throttle chop is to calibrate your main jet at wide open throttle. To do this you need to maintain full throttle in top gear for a period long enough for the spark plug to clear out any richness it may have experienced at other throttle settings. Once you do that you will at the same moment pull in the clutch, close the throttle, and actuate the kill switch. This basically stops the piston in time as well as entering contaminates like raw fuel. Coast to the side and pull and read your spark plug. Decide if you want richer or leaner and change your jet as needed. It is helpful to record a log of what jet yielded what results. Also be aware that there are variables like altitude, temperature, and humidity that can yield different results than what was logged on a given day. But in general the throttle chop is a good way to economically jet your carburetor scientifically with out a dynomometer.

Good luck! And happy jetting!