The 1937 and up W-1 is one of the better 1 barrel downdraft carburetors ever built (MOO). When Carter brought out the W-1 (and its big brother, the W-2) in 1932, they had some "teething" problems. However Carter (unlike some other carburetor companies) recognized the problems, and by 1937 had corrected ALL of the major problems. Changes after 1937 were less dramatic than those previously.
To "thumbnail" some of the major changes:
1934 - major redesign of idle circuit. The initial idle circuit of the 1932 design was a hold-over from the updraft series carburetors, and basically, the idle mixture screw was an inverse measurement. The move of the mixture screw from the top of the casting to the lower section of the casting allowed use of the type idle circuit used by Carter until the end of the O.E. Carter carburetor.
1936 - change to 3 screws holding the airhorn eliminated breakage due to instability.
1937 - change to 4 screws holding the bowl cover eliminated warpage of the bowl cover (another company SHOULD have taken note of this!).
1941 - change to flat accelerator pump. This change was not an "improvement" per se, but was a change which allowed for a slight reduction in the cost of production (and later rebuilding - then); as the cost of the complete "machine assembled" accelerator pump was less (then) than the labor to assemble the older style pump.
1949 - major change to accelerator pump linkage (why, I haven't a clue); plus the addition of the link from the choke to the throttle, which acts as a manual "fast idle". Many like to use the 1949 carburetor as the center carb on a 3x1 aftermarket setup because of the fast idle feature; and use the 1941-1948 carbs as the end carbs. The disadvantage of the 1949 carb is that the accelerator pump for the 1949 carb is unique in design; and as far as I am aware, unavailable except from us. We hand-make the pump in the shop upon order. This makes the 1949 the most expensive of all of the W-1 units to rebuild.
The major problem today with the W-1 is simply ignorance (certainly fixable). Often, people assume that, since most parts physically will interchange among the different models, that the interchange will work. The calibrations were "tweaked" with almost every year. A 1935 metering rod may not work with a 1936 main jet; even though, unless one checks each item against the specs, they "look" the same. There are also some wear issues with the earlier units, but these issues will be corrected by any competant mechanic.
With the exception of the 1932 and 1933; ALL, if properly rebuilt will perform extremely well. The 1932 and 1933 normally have some idle issues, but will run very well above idle.
As with any other carburetor, if one uses ethanol, it may be necessary to "fatten" the calibration slightly (for E-10). Fortunately with the W-1, this can be done by replacing parts.
Jon.
