RAGGED MOTO TECHNICAL TOOLS
Carburetor Jet Size Calculator
Baseline jetting recommendations for modified motorcycle carburetors.
FINE-TUNING ADJUSTMENTS
WHEN CORRECTLY SET
Instant throttle response right off idle, a smooth and steady tick-over, and quick starting.
Instant throttle response right off idle, a smooth and steady tick-over, and quick starting.
Hesitation when opening the throttle from idle
→ Turn the air/fuel screw in ¼ turn increments to add more fuel; fit a larger pilot jet if the screw is already at its adjustment limit.
→ Turn the air/fuel screw in ¼ turn increments to add more fuel; fit a larger pilot jet if the screw is already at its adjustment limit.
Idle is uneven or keeps changing
→ The mixture is too lean (too much air). Add fuel using the air/fuel screw in ¼ turn increments, or install a larger pilot jet if it won’t settle.
→ The mixture is too lean (too much air). Add fuel using the air/fuel screw in ¼ turn increments, or install a larger pilot jet if it won’t settle.
Engine sounds muffled, splutters, or smells like unburnt fuel at idle
→ The mixture is too rich (too much fuel). Reduce fuel using the air/fuel screw in ¼ turn increments, or step down one pilot jet size.
→ The mixture is too rich (too much fuel). Reduce fuel using the air/fuel screw in ¼ turn increments, or step down one pilot jet size.
WHEN CORRECTLY SET
Smooth, strong power delivery from ¼ to ¾ throttle with clean acceleration, no flat spots and a crisp engine note.
Smooth, strong power delivery from ¼ to ¾ throttle with clean acceleration, no flat spots and a crisp engine note.
Flat spot or hesitation when rolling on the throttle.
→ The mixture is too lean. Raise the needle one clip position (move clip down) to add fuel.
→ The mixture is too lean. Raise the needle one clip position (move clip down) to add fuel.
Engine feels sluggish, splutters, or takes a moment to clear.
→ The mixture is too rich. Lower the needle one clip position (move clip up) to reduce fuel.
→ The mixture is too rich. Lower the needle one clip position (move clip up) to reduce fuel.
WHEN CORRECTLY SET
Clean, full-power acceleration at wide-open throttle with the engine pulling freely through the entire rev range.
Clean, full-power acceleration at wide-open throttle with the engine pulling freely through the entire rev range.
Engine feels flat or loses power at ¾ to full throttle
→ The mixture is too lean (too much air). Increase the main jet one size to add fuel.
→ The mixture is too lean (too much air). Increase the main jet one size to add fuel.
Engine splutters, struggles or fails to rev out at full throttle
→ The mixture is too rich (too much fuel). Decrease the main jet one size to reduce fuel.
→ The mixture is too rich (too much fuel). Decrease the main jet one size to reduce fuel.
Fine-tuning: Change one adjustment at a time and retest before making another change.
Looking for bike-specific baseline jetting data?