Does anyone know, or have a good theory on why the Autolite 4100 4V carburetor was dropped in the late 1960s? I know the Autolite 4300 replaced it, but it wasn't near as good and didn't last too long. Meanwhile, the Autolite 2100 2V carburetor continued on through the 1970s and became the Motorcraft 2150 and even later had "feedback" versions into the 1980s.

The Autolite 2100 and 4100 were basically the same carburetors, except the 4100 had 2 extra barrels, obviously. Both had hot air chokes and annular boosters, which run almost as well and atomizes fuel almost as well as EFI when set correctly. The 2150 was able to pass 1980s emissions, yet Ford equipped the Mustang with a Motorcraft 4180 (made by Holley) when it went back to a 4V carburetor in 1983. This carburetor only had annular boosters in the primaries and a fully electric choke, as opposed to the better, more efficient design of the Autolite 4100 that had annular boosters in both the primaries and secondaries and a thermostatic hot air choke that opened and closed based on engine temperature.

I wonder why Ford chose to use an inferior Holley carburetor for the Mustang and didn't bring back the Autolite 4100 design and update it the way they did the 2150?

 

If I had to hazard a guess it would be a four letter word... SMOG. Don't ask me why but that is what did in a lot of things in the 70's when the laws changed but the auto companies were way behind the eight ball in technological advances. Just think I thought 300 HP cars were a thing of the past by 1975 and now we have cars pushing past 500 HP off the shelf.

 

If SMOG was the reason, then why did the Autolite 2100/Motorcraft 2150 stick around until the mid 1980s?

The Autolite 4100 and Autolite 2100 were the same design except for the secondaries, and the later Motorcraft 2150 was the same as the older Autolite 2100, except it was updated with all the SMOG components to make it into the mid 1980s, right up to the 2150A and the electronic "feedback" carburetor.

Why wasn't the Autolite 4100 updated the way the Autolite 2100 was updated? Why wasn't there an "Motorcraft 4150" similar to the later Motorcraft 2150 carburetor?

 

Actually I'll take back the comment about smog since the last time Ford used the 4100 was in 1967. My 67 Park Lane has a Autolite 4300. My 68 Cougar came with a 4300. Apparently Ford made some design changes that they felt were an improvement over the 4100. Of course time proved that wrong. Then when Ford stopped using carbs altogether the design for the annular venturis was sold to Holley. Holley then made the 4010 which was pretty much a 4100. Holley then discontinued the carb a few years later for lack of sales which had nothing to do with performance but with the non-Holley look. As of 4 months ago my Cougar now runs a 4100 with the Edelbrock put on the back shelf. I'd take my Ford-Holley carb from 1972 over the Edelbrock any day but not over the 4100.

 

The Holley's make more power and parts are much easier to obtain. I'm not a big fan of the 4180, I prefer the 4160.

It was cheaper to let Holley to the R&D on the later models like the 83-85 Mustang GT and trucks to keep the EPA happy.
I always had good luck with the 4300's back in the day.