Model A & B

Ford Garage

Zenith Carburetor Jet Sizes & Flow Rates

All original Model A and B Ford Zenith and Holley carburetor jets had the orifice size number stamped somewhere on the jet, making identification easy. No reproduction jets have the jet numbers on them.

The original Ford / Zenith carburetor jet number found stamped on the jet is the jet orifice size as expressed in 0.05 mm increments. For example, a jet marked number '18' has an orifice diameter of (18)*(0.05) = 0.9 mm = 0.035 inch.

The various specifications reported by other sources include flow rates and/or orifice sizes. Ford originally specified the flow rates using a head pressure of 37-1/4 inch of water on the detail drawings, but nearly all recent articles and specifications published thereafter use a 36 inch head pressure of water as the reference pressure. I don't know why the difference, but it is something to be aware of.

Flow rates are expressed in cc/min (e.g., 135-145) and orifice sizes are typically either decimal inches (e.g., 0.035) or Wire Gauge number drill size (e.g., #63).


Summarized below are some of the published flow numbers recommended by various carb rebuilders and experts in the hobby, as well as the original Ford specifications. Flow rates are in cubic centimeters/minute (milliliters/minute).

You can make your own comparisons and conclusions, and establish your own targets. Hopefully this will be helpful in guiding your own carburetor tuning activities.

Model A Zenith Carburetor ~ Jet Sizes & Flow Rates

Quoted Source Idle
A-9542
Main
A-9534
Cap
A-9538
Comp
A-9575
Ford Drawing
Normal Altitude
(37-1/4" Head Pressure)
44 - 55
0.0216 to 0.0236
Marked '11'
165 - 169
Marked '20'
180 - 190
Marked '20'
157 - 161
Marked '19'
Ford Drawing
High Altitude
(37-1/4" Head Pressure)
44 - 55
0.0216 to 0.0236
Marked '11'
157 - 161
Marked '19.5'
180 - 190
Marked '20'
157 - 161
Marked '19'
Paul Moller
(36" Head Pressure)
#75
0.021
#65
0.035
#64
0.036
#63
0.037
Chris Pelikan
(36" Head Pressure)
44 - 48
#75-74
150 - 160
170-185
#61-60
170 - 190
#62
155 - 165
#64-63
Al Blatter
NOS Jets = (full rich)
(36" Head Pressure)
46 - 50
159 - 163
176 - 180
152 - 156
Al Blatter
Recommendations
(36" Head Pressure)
46 - 50
130 - 145
176 - 180
152 - 156
Tom Endy 44 - 48
140 - 150
150 - 180
138 - 142
Steve Pargeter
(36" Head Pressure)
44 - 48
#76
0.021
150 - 160
#65
0.035
150 - 185
#64
0.036
138 - 142
#63
0.037
Howard Taylor 48 - 49 160 - 165 165 - 170 150 - 152
Larry Brumfield
(36" Head Pressure)
46 - 50 159 - 163 176 - 180 152 - 156
Darrel Beavers #75
0.021
#63
0.037
#63
0.037
#65
0.035

Model B Zenith Carburetor ~ Jet Sizes & Flow Rates

Quoted Source Idle
B-9542
Main
B-9534
Cap
B-9538
Comp
B-9575
Power
B-9594
Ford Drawing
Normal Altitude
(37-1/4" Head Pressure)
0.0236 - 0.0241
Marked '12'
148 - 152
Marked '19'
#50 drill
Marked '35'
139 - 143
Marked '18'
131 - 135
Marked '18'
Ford Drawing
High Altitude
(37-1/4" Head Pressure)
0.0236 - 0.0241
Marked '12'
131 - 135
Marked '18'
#50 drill
Marked '35'
120 - 124
Marked '17'
131 - 135
Marked '18'
Dave Renner
(37-1/4" Head Pressure)
44 - 48 138 - 144 320 - 478 112 - 120 112 - 120
Gordon Biggar
Rex Reheis
43 - 47
#73
136 - 142
#63
0.037
372 - 462
#50
110 - 118
#65
0.035
110 - 118
#65
0.035
Ben Nieman 60
0.022
162
0.035
520 135 - 145
0.033
145
0.033

More Zenith carburetor information on Ford Garage:

  1. Model A Zenith Carburetor Theory of Operation
  2. Model A Zenith Carburetor Numbering
  3. Model A Zenith Carburetor A-9545 Secondary Well Variations
  4. Model A Carburetor Float Weights
  5. Model A Zenith Carburetor GAV Wrench
  6. Model B & 46 Zenith Carburetor Parts Catalog Illustrations
  7. Model B & 46 Zenith Carburetor Assembly Drawings
  8. Model B & 46 Zenith Carburetor Float Details
  9. Model B & 46 Zenith Float Valve Orifice Details
  10. Model B & 46 Zenith Carburetor Power Jet Circuit
  11. Model B & 46 Zenith Carburetor Power Jet Tube
  12. Model B & 46 Zenith Carburetor Power Jet Tube Instructions
  13. Model B & 46 Zenith Carburetor Catalog Data
  14. Model B & 46 NOS Zenith Carburetor
  15. Model B & 46 Zenith Carburetor Upper Casting Variations
  16. For more Model A & B Zenith carburetor web pages, use the Site Search box at the top or bottom of this web page.

May 2005