Autolite 2100 bbl carburetors are pretty much a set and forget affair, however, they do have a notorious weak spot-- throttle shaft wear. After years of back and forth rotation, the steel shaft eventually wears the aluminum bores from round to egg shaped. Mechanically, the carburetor can handle even a large amount of slop, although severe wear can cause the throttle to bind. The real problem with even a slight amount of wear is the resulting vacuum leak, which because the shaft moves, is inconsistent. This makes tuning the idle mixture nearly impossible. The orthodox repair for this condition involves reaming the shaft bores oversized and installing brass bushings to bring things back to spec. OR… You can use my cheapskate solution, which although it involves some machining, it’s the kind that can be done by hand or with a low tech drill press. The process is pretty simple.
First, remove the throttle shaft from the carburetor. Next, use a 9/16 drill bit to countersink the throttle shaft bores on each side of the carburetor. Work slowly! You want to remove only as much material as necessary to seat half of the width of your o ring. Clean up any burrs and dab o spot of grease on the newly drilled surfaces.
So far (assuming you don’t have to buy the drill bit) the cost is free, but here’s where you have to outlay some minor cash. Purchase 2 viton o rings, 3/8 ID, 9/16 OD from your favorite hardware or auto shop, along with 1 3/8" ID shaft collar and 2 1/32 thick 3/8 nylon washers.
Reinstall the throttle shaft, first slipping one of the washers and an o ring onto the shaft (that’s going to seal up the linkage side).
On the other side, before installing the fast idle lever, slide the other o ring, then the other washer, and finally the shaft collar onto the staff. Push the shaft collar up against the washer and o ring just so it puts pressure on the o ring and tighten the set screw to hold it in place.
That’s it. I did this to all thee carbs on my 68 and I couldn’t believe how much more smoothly it idles.
