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1923 Pierce Carburetor Info Sought


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I recently restored the carburetor for a 1923 Pierce-Arrow. The customer now complains that it runs much too rich . . . and I have thus far been unable to determine why. In the course of the restoration, I did nothing to alter the metering characteristics of this carburetor, nor did I "tighten-up" the reed valves found under the bug screen. All three appeared to have differently-calibrated (graduated) tension so I cleaned them up but otherwise left them strictly as they were.

Since I am not sure how to identify this carb, here is a photo; click on image to enlarge:


There are a couple of capital "T"s and one capital "U" stamped into the main casting, but other than the word "PIERCE" and some patent dates on the bowl lid, I can find nothing to positively I.D. it.

When I fill the carburetor to the correct level with test fluid, none leaks out unless I tilt it dramatically. When I shut off all three mixture adjustments (high speed, low speed and another which I cannot identify) as a test and apply compressed air to the fixed air inlet, no test fluid is seen to blow out past the throttle valve. I am mystified as to why/how it can run rich.

Does anyone have any literature about these carburetors? Any breakdowns, cutaways or technical info (such as it existed back then)? Failing that, has anyone had any experience with these units? I have been in business for 25 years and have never encountered one.

Please let me know if you have any info to share ASAP as my customer needs to prep this car for winter storage very soon. You may contact me any way you choose.

And no, I don't know why the image is displayed upside-down below; I have tried to delete it but it does no good.

Jeff Dreibus

The Old Carb Doctor




Edited by carbdoc (see edit history)
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Jeff, I restored two of these carb's years ago and found them to be very reliable. The problem could be nothing that you have done, or that you are aware of anyway. Perhaps one of the reed valves is sticking, and staying closed, even though it was cleaned. Yes, as you mentioned, each reed is of a different thickness or tension requirement and requires more suction to open it as the engine speeds up; i.e the reeds allowing air to be drawn into the carb. as they open.). Thus if the reeds are not opening enough the engine would run rich. Also, as you are aware, there is no choke on this carburetor. When starting the engine in cold weather, an injector allows raw gas into the intake manifold for starting. (This injector is basically a spring loaded needle valve that when pulled back from it's seat, allows raw gas to flow into the intake manifold for easier starting. It sits on top of the intake manifold.). It could be that this injector is not seating properly and is thus allowing gas into the manifold while the engine is running. Hope this helps; regards; Jerry Janson

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Thanks so much, Jerry --- this is helpful info!

I checked the air valves this morning: all centered, no sticking, plenty of opening distance.

I will copy your discussion of the injector to the customer. As an aside, the principle you describe reminds me of "starter injector" on my 1984 BMW which was built 60 years later!


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  • 2 weeks later...

Jeff, the adjustment rod on the very bottom of the carb that gets the enrichment cable is best adjusted engine running. many times you have to move the arm after you get final adjustment. you could leave the arm off, adjust for warm run idle, then install for full adjustment. Moving this is like any modern carb as you move the seat screw you get a feel for the final distance. The cold start valve mentioned above is closed or open, no adjustment, strong spring pressure. I don't think you would find a problem there. The other thing to blacken plugs is very retarded engine timing,nothing to do with the carb! Karl

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