Mikuni Pilot Jet Drill-Size Reference: Diameter Equivalents and Cautions
Important: do not drill genuine Mikuni jets. Jet-number markings are not universal or interchangeable with orifice diameter, drill size, or flow rate. Buy the correct genuine jet for the carburetor and use the manufacturer’s tuning information.
Diameter Equivalents and Nearest Drill Sizes
The table compares selected geometric orifice diameters with decimal inches and the nearest listed drill size. It is a dimensional reference only: it does not convert a Mikuni jet number, predict fuel flow, or recommend modifying a jet. A drill may be smaller or larger than the reference diameter as shown.
| 0.35 mm | 0.0138 in | #80 | 0.3429 mm | -0.0071 mm (smaller) |
|---|---|---|---|---|
| 0.40 mm | 0.0157 in | 1/64 in | 0.3969 mm | -0.0031 mm (smaller) |
| 0.45 mm | 0.0177 in | #77 | 0.4572 mm | +0.0072 mm (larger) |
| 0.50 mm | 0.0197 in | #76 | 0.5080 mm | +0.0080 mm (larger) |
| 0.55 mm | 0.0217 in | #75 | 0.5334 mm | -0.0166 mm (smaller) |
| 0.60 mm | 0.0236 in | #73 | 0.6096 mm | +0.0096 mm (larger) |
| 0.65 mm | 0.0256 in | #71 | 0.6604 mm | +0.0104 mm (larger) |
| 0.70 mm | 0.0276 in | #70 | 0.7112 mm | +0.0112 mm (larger) |
| 0.80 mm | 0.0315 in | 1/32 in | 0.7938 mm | -0.0062 mm (smaller) |
| 0.90 mm | 0.0354 in | #65 | 0.8890 mm | -0.0110 mm (smaller) |
| 1.00 mm | 0.0394 in | #61 | 0.9906 mm | -0.0094 mm (smaller) |
| 1.20 mm | 0.0472 in | 3/64 in | 1.1906 mm | -0.0094 mm (smaller) |
12 rows
Scroll horizontally to view all columns.
Why Jet Numbers Do Not Convert Directly
Jet numbering systems and flow behavior differ by manufacturer, series, and construction. Even matching nominal diameters do not guarantee equal fuel delivery. Drilling can leave a tapered, off-center, burred, or out-of-round opening and permanently alter metering. Use the exact carburetor/jet series and genuine replacement part; do not use this table as a jet-sizing or tuning chart.
References
Drill-size decimal equivalents; jet numbering and cross-brand conversion limitations; Mikunioz guidance on genuine Mikuni pilot jets.
