Enter your Engine Displacement, Cylinders, Altitude, Temperature, Air Filter Type, and Current Jet Sizes into the Motorcycle Jet Size Calculator to get a Recommended Main Jet, Pilot Jet, and required Jetting Change for optimal tuning.
Recommended Main Jet
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Recommended Pilot Jet
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Jetting Change
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Target A/F Ratio
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Signs include poor throttle response, black smoke from exhaust, excessive fuel consumption, difficulty starting, or if you've modified the air intake or exhaust system.
The main jet controls fuel flow at wide open throttle (3/4 to full throttle), while the pilot jet controls fuel flow at idle and low throttle positions (up to 1/4 throttle).
Higher altitude has thinner air, requiring smaller jets to maintain proper air-fuel mixture. For every 2000 feet of elevation gain, you typically need to reduce jet size by 5-10%.
This calculator provides general recommendations for most motorcycle carburetors. However, specific carburetors may have unique characteristics requiring fine-tuning through testing.
Jets too large cause rich running (black exhaust, fouled plugs, poor fuel economy). Jets too small cause lean running (overheating, poor performance, potential engine damage).
It's best to change one at a time and test. Start with the circuit that shows the most problems - main jet for high RPM issues, pilot jet for idle and low-speed problems.
Cold air is denser and requires larger jets, while hot air is thinner and needs smaller jets. A 20°F temperature change can require a 2-5% jet size adjustment.
You'll need basic hand tools to remove the carburetor, a jet removal tool or small screwdriver, and replacement jets. Always have a selection of jet sizes for tuning.