Carb Jetting Guide
Calculate main and pilot jet adjustments for altitude and temperature. Includes a needle clip reference and symptom diagnosis guide.
Riding Elevation
Ambient Temperature (°F)
Stock / Baseline Jet Sizes
Air Density at 0 ft / 70°F: 99.0%
Recommended Main
132
No change
Recommended Pilot
42
No change
Needle Clip
Stock
No change
Needle Clip Position Reference
Affects mixture at 1/4–3/4 throttle
| Clip 1 (top) | Richest — needle hangs lower in jet needle |
| Clip 2 | Richer than stock |
| Clip 3 (stock) | Stock / baseline |
| Clip 4 | Leaner than stock |
| Clip 5 (bottom) | Leanest — needle sits higher in jet needle |
Symptom Diagnosis
Rich (all throttle)
- •Black, sooty spark plug
- •Rich smell / black smoke
- •Sluggish, blubbery top end
- •Bike runs better when choke removed
Fix: Go down in main jet size or raise needle clip position
Lean (all throttle)
- •White / gray plug, overheating
- •Flat spot or hesitation at WOT
- •Pops / backfires on decel
- •Engine runs hot, exhaust glowing
Fix: Go up in main jet size or lower needle clip position
Rich (idle / low)
- •Plug fouling at idle
- •Rough idle, need to idle high
- •Black smoke at idle
Fix: Lean pilot jet or turn air screw OUT (counterclockwise)
Lean (idle / low)
- •Popping on decel
- •Hard to start cold
- •Idle surges or hunts
- •Throttle response stumble off idle
Fix: Richer pilot jet or turn air screw IN (clockwise)
Notes
• Jet sizes are approximate — always verify with a plug chop and road test before finalizing.
• Aftermarket exhausts and air filters typically require richer main and pilot jets.
• Air screw (fuel screw): OUT (counterclockwise) = richer at idle. Start at 2.5 turns out from seated.
• Slide cutaway affects off-idle to 1/4 throttle. A larger number = leaner in that range.