Is My Bike Running Rich or Lean? To determine whether you need to re-jet the carb you can simply look at the spark plugs. Take the plugs out and if they look clean you're good to go. However, if you see black soot then you're running rich - meaning too much fuel - if you see A bright white insulator - meaning it is running too lean.
You can also determine if you need to jet the carb based on how the bike rides. If your dirt bike tends to be sluggish when you punch it and/or backfires when you open it up a bit, you're probably too rich. However, if your bike can take off in a sprint but lacks overall power, then you've got too much air.
The carburetor consists of four components: Which you can learn more about in this video Carburetor Operation
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