I apologize in advance to those who have read some of this before.
The official doctrine for the entire 1933-52 1-1/4" 3-bolt "M" series is well know; Palmer and the factory literature all agree. There are only 2 variants:
1. 1936-39 EL M5, 55 etc. with its own body casting, main nozzle, etc.
2. everything else, regardless of engine size or state of tune. Not only do there appear to be no machining diffs in Palmer between these (except internal vs. external air correction), but only a single replacement body (1226-33) and a single main nozzle (27331-33) fits everything.
This is the puzzle: how can motors of 45", 74" and 80", with cams from very small (stock VL) to mild (1939 WLDR) have acceptable mixture using exactly the same parts? If they're all the same, why are there more than 2 part numbers (1 internal air correction such as M-88, 1 external such as M-51)?
I have a feeling that, pre-1940 (when the OHV motor became the focus) the carburetors based on the same basic casting, but were more specific in terms of machining to better suit the engine.
This must have driven the dealers crazy, since the diffs would be invisible, and have no apparent effect on initial examination.
I'd like to hear from anyone who has, or seen, a 1-1/4" that appears unmolested and can give me a few measurements. In particular, I'd like the air correction opening size for the external types (M-51), just drop drill shanks in it until it won't fit (doesn't need to be exact). All I've ever seen are 3/16" (.1875"), and I'm looking for smaller ones especially in early carbs such as M21, 31, 41.
I'd also like confirmation on the exact slot size of the air hole in the front edge of the M-88 etc. It's about 5/16" wide, but the ones I have are not only not the same size but arre are corroded. What's the height?
I'm going to create a page of Linkert data for public access, including all factory stuff I can find complete with pictures.
Thanks in advance for any help.
Add up the area of the four #57 holes on the nozzle, and compare that with the area of a 3/16" vent hole. It's over-kill, thus it has no effect upon different sizes of motors. It is not a metering orifice; it is "atmosphere".
Please consider how small the vent became with the evolution of the M35 to M35T to M35TP, yet they still vented Big Twins.
A parameter that IS quite enigmatic, however, is the various bore diameters for the lowspeed needle "well".
Note how large it is for the M-5 compared to Flatty models.
And later, why was the well choked to a smaller diameter deep in the body when the M74B (with serifs) changed to the M74B (no serifs)?
If the hole in the spring collar (obstructed by the needle shank) is a metering limiter for incoming air to the well, why should the bore diameter make a difference?
(And if the spring collar hole is so critical, why is the seat for the spring collar so often rough-cast, allowing air beneath it?)
We may never know.