Mikuni Pilot Jet Drill Size Chart
Quick answer: do not drill genuine Mikuni jets as a first choice. Jet numbers, orifice size, and flow are not perfectly interchangeable across brands and jet styles. Buy the correct pilot jet when possible, and use drill-size charts only for reference, emergency tuning, or identifying an already-modified jet.
Jet Size To Drill Size Reference
| Jet size / mm | Decimal inch | Nearest numbered drill | Reference note |
|---|---|---|---|
| 0.35 mm | 0.0138 in | #80 is larger | Small pilot range |
| 0.40 mm | 0.0157 in | 1/64 in is close | Small pilot range |
| 0.45 mm | 0.0177 in | #77 is larger | Small pilot range |
| 0.50 mm | 0.0197 in | #76 is close | Common pilot range |
| 0.55 mm | 0.0217 in | #74 is larger | Common pilot range |
| 0.60 mm | 0.0236 in | #73 is close | Common pilot range |
| 0.65 mm | 0.0256 in | #71 is close | Large pilot/small main range |
| 0.70 mm | 0.0276 in | #70 is close | Large pilot/small main range |
| 0.80 mm | 0.0315 in | #68 is close | Main jet reference range |
| 0.90 mm | 0.0354 in | #64 is close | Main jet reference range |
| 1.00 mm | 0.0394 in | #60 is slightly larger | Main jet reference range |
| 1.20 mm | 0.0472 in | 3/64 in is close | Main jet reference range |
Jet Tuning Cautions
- Drilling can make an out-of-round or burred orifice and can change flow unpredictably.
- Once a jet is too large, it cannot be made smaller reliably.
- Use genuine jets and tune in controlled steps with plug readings, AFR data, or manufacturer guidance.
- Do not assume Mikuni, Keihin, Dynojet, and copy jets use equivalent numbering.
Source Notes
Drill equivalents and cautions were checked against jet/drill references including Jets R Us drill size decimal equivalents, Jets R Us jet-size conversion cautions, and Mikunioz guidance warning against drilling genuine Mikuni jets. Treat the table as a reference, not a recommendation to drill jets.
