How to check your jetting with plug chops

A plug chop simply means looking at the sparkplug to determine how you are jetted at a particular throttle stage. The only tricky part is in isolating the throttle stage. Before starting, clean your sparkplug and filter and warm the bike up.

To check the main jet, which operates from 1/2 to full throttle, get the scooter up to a steady full throttle or near to it for a good few seconds, then simultaneously pull in the clutch and kill the engine. Don't let the motor drag you to a stop, or fall to an idle, because you want to isolate the plug color at full throttle.

Get off and check the sparkplug color. (Links on our tech page.) It should be a light chocolate color. If it's white, the air/fuel mixture is too lean and you need a bigger main jet. If it's black or really dark brown, the air/fuel mixture is too rich and a smaller main jet is needed. If you need to change jets, change by one size, and do another run.