About ToolSite
Built by powersports enthusiasts who got tired of guessing jet sizes at altitude.
Why We Built This
The calculator started as a spreadsheet. We'd load up bikes for a trip to the Colorado Rockies, know we needed to rejet, and spend an hour cross-referencing Dynojet charts, Mikuni jetting guides, and an old FAA density altitude formula. The math was always the same — it just took too long to do manually every time.
So we built a proper tool. Then we published it so other riders wouldn't have to do what we did. That was the beginning of CarburetorJetSizeCalculator.com.
The team behind it has 15+ years of carburetor tuning experience across motocross bikes, enduro machines, ATVs, karts, and vintage two-strokes. We've made the full-lean mistake (cracked piston, learned that lesson once). We've ridden at sea level and at 11,000 ft and everywhere between. The calculator reflects what actually works on the trail, not just what looks good on paper.
How We Verify the Formulas
Every formula in the calculator traces back to an authoritative source. We don't invent correction factors — we derive them from:
- Dynojet Research Jet Kit Installation Guide — the industry standard for aftermarket jetting calculations, used by shops worldwide
- Mikuni Carburetor Technical Reference (HSR Series Tuning Manual) — Mikuni's own engineering documentation for jet sizing and altitude correction
- FAA Advisory Circular AC 00-6B (Aviation Weather) — the definitive reference for density altitude calculations, the same standard pilots use
The core physics — the ideal gas law, ISA (International Standard Atmosphere), the August-Roche-Magnus approximation for humidity correction — are well-established science. Our implementation cross-references all three sources to make sure the constants, rounding, and jet size increments align with real-world carburetor specifications (2.5 µm steps for Keihin and Mikuni).
Niche-Specific Tool
This calculator does one thing: carburetor jet sizing for altitude, temperature, and engine modifications. We don't try to do everything — we try to do this exactly right.
Free, Always
No paywalls. No mandatory sign-up. No premium tier. Riders shouldn't have to pay to access a physics calculation they could do themselves — we just make it faster.
Accuracy First
We verify our formulas against Dynojet, Mikuni, and FAA sources before publishing any change. If we find an error, we fix it and note it in the change log.
Education, Not Just Answers
The blog explains the physics behind jetting so you understand why a change works, not just what to change. A rider who understands density altitude makes better decisions in the field.
Our Tools & Resources
The carburetor jet size calculator is the core tool — input your current setup and conditions, get a recommended main jet, pilot jet guidance, needle clip suggestion, and density altitude.
The jetting blog covers everything around the calculator: how to read a spark plug, when to call a dyno tuner, the difference between pilot and main jets, and seasonal jetting guides for year-round riders.
Get in Touch
Found an error in the calculation? Have a jetting question, or want to report an edge case we should handle? We read every email.
contact@example.com