Stromberg OA-1 Carburetor Aftermarket Adjusting Instructions Sought

[hddennis]

I've acquired and mounted a Stromberg OA-1 aftermarket carburetor on my 1917 Maxwell. It is an aftermarket carburetor listed as a replacement for 1918- 1922 Maxwell cars. I have no idea why 1917 cars aren't listed as they are exactly the same as 1918 models. I have a copy of the factory mounting and adjusting instructions but would like to know if any period literature shows instructions that cover more, like adjusting the float level. Period internal  illustrations would be welcome as well.

 

Howard Dennis 

[carbking]

Float adjustment for early brass updraft carburetors

 

Most PLAIN TUBE early brass carburetors may use the following guide (in the absence of anything else) to adjust the float.

 

(1) With the carburetor on the work bench, measure through the main venturi from the mounting flange to the top of the main discharge nozzle, and record this dimension.

(2) Measure this same dimension from the top of the flange on the OUTSIDE of the carburetor, and make a scribe mark on the body showing this dimension. You may find some previous mechanic has already made such a mark.

(3) Acquire a "fuel level gauge", such as the one pictured in the "virtual carburetor museum" on my website:

 

Fuel level gauge

 

OR fabricate a functional replacement.

 

A functional replacement may be made using a brass fitting combination and a length of clear plastic tubing to make a "J" tube. Remember the upper end is open.

 

(4) Remove the bowl drain and attach the fuel level gauge or functional replacement.

(5) Measure the distance from the fuel source on the vehicle to the top of the carburetor bowl.

(6) Acquire an external gravity feed fuel source and fix it on your workbench the exact distance measured in (5) above. WARNING: if you are even thinking about the possibility of considering trying to use an electric fuel pump with this carburetor, pause the float adjustment procedure, and install an automatic halon underhood fire extinguisher before finishing the adjustment!

(7) Add some fuel to the external fuel source. The fuel should now feed the carburetor. Compare the level of fuel in the tube to the scribe mark. The fuel level needs to be 1/8 inch (0.125 inch) BELOW the scribe mark.

(8) Adjust the fuel needle in the carburetor to adjust. This can be tricky, as some of the collars are soldered to the needle. IF YOU ARE CLOSE, you can sometimes make a small adjustment by changing the thickness of the fuel valve seat gasket, to raise or lower the seat. The needles with the threaded collars are much easier to adjust.

 

The first item (6) above is IMPORTANT! Both Stromberg and Zenith issued different fuel valve seat orifices for different fuel head pressures, depending on this distance.

 

Jon

 

 

 

[hddennis]

Thanks Jon. I was studying the factory parts list and noticed P-26 is labeled as float chamber fuel level plug. Am I right in assuming that the fuel level should be adjusted so that it falls just below the threads of this hole?

 

Howard Dennis

[carbking]

In the case of the OA-1, yes. Not many old brass carbs have the sight plug.

 

Jon.

[hddennis]

38 minutes ago, carbking said:

In the case of the OA-1, yes. Not many old brass carbs have the sight plug.

 

Jon.

Your right Jon, I can't remember seeing another and at first glance thought it must have been an access hole for boring a fuel passage during manufacturing.

 

Howard Dennis

[Peter R.]

Some fuel level gauges….