Rochester Carburetor Jet Size Chart & Drill Size Guide
This guide provides a practical reference for Rochester carburetor jet sizes and drill sizes commonly used for cleaning, checking, and careful tuning work. Rochester carburetors include several different families, so this guide should be used as a practical drill-size reference rather than a guaranteed manufacturer specification.
About Rochester Carburetors
Rochester carburetors were widely used on many General Motors vehicles and related automotive applications. Common Rochester carburetor families include 2-barrel models, 4-barrel models, and the well-known Rochester Quadrajet used on many classic GM cars and trucks.
Rochester and Quadrajet tuning can involve more than just changing the jet opening. In many Quadrajet applications, the primary jet works together with a metering rod, so the jet-and-rod combination affects fuel metering. Always verify the specific carburetor model, jet type, metering rod combination, and application before cleaning, checking, or modifying a jet.
Which Drill Set Is Right for Rochester Jet Work?
For Rochester carburetor jet checking, cleaning, and careful sizing work, choose a drill set based on the jet range and carburetor type you expect to work with.
Best Starting Point for Many Rochester and Quadrajet Main Jets: HS1 50 Pc Carburetor Jet Drill Set
Covers a broad .040" through .125" range, which is useful for many larger automotive carburetor jet sizes, including common Rochester and Quadrajet-style main jet work.
Working on Smaller Carburetor Jets?
The 20 Pc Selected Sizes Carburetor Jet Drill Set covers selected sizes from .0135" through .071", useful for smaller carburetor jet work, small engines, motorcycles, scooters, and similar applications.
Need More Continuous Numbered-Drill Coverage?
The 25 Pc #75–#51 Carburetor Jet Drill Set gives a broader numbered-drill range for general carburetor jet checking, cleaning, and careful tuning.
Want Backup Drills in Each Size?
The D7 50-piece #80–#56 set includes 25 sizes with two drills per size, useful when working with small, brittle carbide drills and smaller jet ranges.
Not Sure Which Range You Need?
If you work on several carburetor brands, smaller jets, larger jets, Holley-style ranges, Rochester/Quadrajet applications, or Ford Model A Zenith carburetors, compare the full collection before ordering.
Important: carbide drills are brittle precision tools. Use light pressure, keep the drill straight, and avoid enlarging jets unintentionally during cleaning.
Rochester Jet Size Chart & Drill Size Reference
Many Rochester and Quadrajet jet sizes are identified by stamped numbers. These numbers are often used as practical size references, but they should not be treated as guaranteed drill-diameter specifications. Actual fuel flow can vary depending on jet design, metering rod combination, entry shape, exit shape, finish, and condition.
The Nearest Drill Size Reference column shows the closest practical drill size or drill range for comparison. It is meant for checking and reference only; always verify the actual jet and carburetor application before modifying anything.
| Jet Reference Size | Approx. Inches | Nearest Drill Size Reference |
|---|---|---|
| 65 | 0.065" | 1.65 mm range |
| 67 | 0.067" | #51 range |
| 69 | 0.069" | 1.75 mm range |
| 70 | 0.070" | 1.80 mm range |
| 71 | 0.071" | 1.80 mm range |
| 73 | 0.073" | 1.85 mm range |
| 75 | 0.075" | 1.90 mm range |
| 77 | 0.077" | 1.95 mm range |
| 79 | 0.079" | 2.00 mm range |
| 80 | 0.080" | 2.00 mm range |
Note: This chart is an approximate drill-size reference. Rochester and Quadrajet jet sizing should always be verified against the specific carburetor, jet, and metering rod combination before modification.
Using Drill Sizes for Rochester Carburetor Jet Work
Precision drill bits are commonly used in carburetor work for cleaning clogged jets, checking approximate jet size, comparing jet openings to known drill diameters, and carefully modifying jet orifices when tuning requires it.
Because drills come in fine size increments, they provide a practical way to work within carburetor jet size ranges. When modifying jets, make small changes and verify results carefully. For many Rochester and Quadrajet applications, also consider how the metering rod interacts with the jet before making permanent changes.
Practical Drill Size Range for Rochester and Quadrajet Jets
Many Rochester and Quadrajet-style automotive main jets fall into larger small-drill ranges than the very small jets used in some motorcycle, scooter, RC, and small-engine carburetors. For this reason, the HS1 .040"–.125" range may be a better starting point for many Rochester and Quadrajet main jet applications.
Smaller selected-size sets may still be useful for other carburetor work, checking smaller passages, or working on mixed carburetor types. If you are unsure which set is best, compare the carburetor jet drill sets before ordering.
Tips for Jet Sizing and Modification
- Use light pressure when working with carbide drills
- Keep the drill straight to avoid making the jet opening oblong
- Always verify size before modifying a jet
- Consider the jet and metering rod combination when working on Quadrajet-style carburetors
- Make small, incremental changes when tuning
- Avoid enlarging jets unintentionally during cleaning
- When in doubt, replace the jet rather than over-drilling it
Conclusion
Understanding the relationship between Rochester jet references and practical drill sizes can make carburetor cleaning, checking, and careful tuning more controlled. Use this chart as an approximate drill-size guide, verify the exact drill size before modifying any jet, and choose the drill set that best matches the range of sizes you need.