Model B
Model A Ford Garage
Zenith Carburetor Power Jet Tube
fordgarage.comPictured here is the power jet tube used in the Model B Ford carburetor. This jet enriches the airflow with added gas in open throttle conditions. It performs the same function as an accelerator pump, but without a pump diaphragm or complicated linkage mechanism.
The tube is immersed in a gas well in the lower carburetor body casting. The gas is metered into the well by the power jet orifice in the float chamber. The suction on the tube is controlled by an air passage valve machined into the throttle shaft and upper body.
fordgarage.comIt is very common to find broken, damaged, or missing tubes in Model B carburetors. Unfortunately, the original tube is made from fragile brass and is pressed into the upper carburetor body casting. The tubes are easily damaged when disassembling or handling the upper body.
A non-functioning power tube negates the potential benefit of the Model B carburetor compared to the Model A Zenith, since the B power tube is what creates the much improved throttle response and power on demand.
There are three primary failure modes of the Model B power jet feature:
- It will not function if the tube is plugged.
- It will not function if the tube is cracked above the fuel level and leaks air.
- It will not function if the air bleed hole in the casting is plugged.
fordgarage.comThe pic above shows the brand new replacement power tube I reproduce from stainless steel tubing. It is the correct OD and length per the original Ford detail drawing researched at the Benson Ford Research Center.
Contrary to conventional wisdom, this tube is not a standard size, nor is it available from hobby stores, old ball point pen cartridges, etc. This is a special size tube and is reproduced to-print with the exception that is made from stainless steel whereas the original was brass. The stainless will not corrode, and is also stronger than the original fragile brass tube.
fordgarage.comWhen the old tube is pulled out for replacement, it is important to also make sure that the air bleed (vent) hole in the casting at the top of the tube is not obstructed. If the vent hole is plugged, the gas well will be air-locked, and the power tube will not be able to function properly.
A #60 number drill bit is the air bleed hole size, as shown above with a drill blank inserted in the vent hole.
Please Click Here to view the power tube installation instructions page.
Please Click Here to read more information about the Model B Zenith carburetor power jet tube circuit.
I sell the power jet tubes on eBay as well as direct with payment through PayPal. They are not available through any catalogs or other outlets. Please contact me for more information or to order.
More related information on Ford Garage:
- Model A & B Zenith Carburetor Jet Sizes & Flow Rates
- Model B & 46 Zenith Carburetor Parts Catalog Illustrations
- Model B & 46 Zenith Carburetor Assembly Drawings
- Model B & 46 Zenith Carburetor Float Details
- Model B & 46 Zenith Float Valve Orifice Details
- Model B & 46 Zenith Carburetor Power Jet Circuit
- Model B & 46 Zenith Carburetor Power Jet Tube Instructions
- Model B & 46 Zenith Carburetor Catalog Data
- Model B & 46 NOS Zenith Carburetor
- Model B & 46 Zenith Carburetor Upper Casting Variations
- For more Model A & B related information, use the Site Search box at the top or bottom of this page.
Vince Falter
February 2004
