Looks like there is a fair amount of "gunk" on the main return spring on the driver's side.  As a rotating coil spring, any debris between coils adds friction and it may be just enough to keep it from closing fully.  However, the spring may also be worn with time.  Can't tell from the pics if your choke mechanism is clear.  Sometimes you can screw the fast idle screw in too far an it will keep the plates open but you can sometimes pull hard to twist it shut on the throttle side.  I would pull the choke heater cover off and verify that everything is free and not hanging - this will help to make sure that the fast idle cam is not sticking as well.

The bushings do indeed wear out and create a way for air to get in to mess with your mixture and idle speed but also can prevent the throttle plates from seating properly under normal spring pressure.  Address the outside issues and if it clears up leave it alone as long as it runs OK.  A professional rebuild will include new bushings where appropriate but this is well above a basic gasket kit.  But it may be a worthwhile investment if you plan to hang on to the car and the carb.  And a disclaimer - I am not a 4100 expert by any stretch.

Ah, I can see the lithium now.  I've seen some corrosion that looks similar as well as a few bug's nests!  Sounds like you've been pretty thorough.  Looking from above or below, how do the throttle plates look - can you see a difference in where they seat when it hangs versus when it closes cleanly?  Is there a mechanical mechanism to force the secondaries closed?  Good luck.

With your description of the play in the throttle shaft...sounds like you have a nice little vaccuum leak. The 4100 shafle bushings are famous for wear. My 4100 did exactly the same and would idle great while the engine was cold. But after a full warm up the idle would jump 200-400 rpm. The tolerances between the bushing and shaft would open up and suck air past. Take carb cleaner and spray the shaft and see if the idle changes any.

I had the main shaft bushings replaced on my 4100 and it made all the diffference. Idles perfect now.
The secondary usually dont need replacement...they dont wear as much.
Cost $50 at the local carb shop.


 

gjz30075 wrote:

......  There could very well be play in the bushings........ 

There are no bushings, gjz. They just bored thru the body casting.  With a repair, they bore the holes larger and insert bushings.  I would be surprised if the bushings were not made out of more suitable bearing material that the material used in the body.

Additionally that C4AF R was made for a '64 big block 352.  You are bound to have issues running it on a 289/302.

Last edited by boomyal (1/19/2014 4:47 PM)

Ah, got it.    Thanks.   The motor is a 331 with AFR 185 heads and an Air Gap.     This Autolite is heads above the Holley that I took off.   The reason I took it off was I just couldn't get rid of a 'tip in' stumble, no matter where the revs were, it surged badly on moderately hard acceleration and out of the box (reman from Holley), the accel pump leaked, the power valve leaked and there were metal shards floating around the bowls and would hang up the floats.      Also the engine always sounded like it had an exhaust leak but I never found one.  I tried everything to tune it, but I think it was cursed.

A simple rebuild on this Autolite with some jetting changes and already the engine is so much smoother, no hesitation anywhere and a real joy to drive.    

So long story short, I'm willing to fix the issues on this carb because I'm 95% ahead of the Holley.

MS, I backed off the fast idle screw alot to clear the cam so I think I'm good there.  I will check again.

Last edited by gjz30075 (1/19/2014 5:02 PM)

Hey boomyal...you are correct sir! The 4100 shafts run on the body material (aluminum) that did indeed wear. When rebushed, a brass or bronze inert is installed and reamed to size.

Also a great 4100 info site: Ed's Carburetor Forum

http://www.network54.com/Forum/88781/

ponch0v wrote:

Hey boomyal...you are correct sir! The 4100 shafts run on the body material (aluminum) that did indeed wear. When rebushed, a brass or bronze inert is installed and reamed to size.

Also a great 4100 info site: Ed's Carburetor Forum

http://www.network54.com/Forum/88781/

That site used to be a whole lot better when a guy named Bill White ran it.  That is where I learned a lot of the ins and outs of the 4100.  It also used to be almost exclusively about Autolites.  IMHO ever since this Ed Jenkins took over, the site has gone down hill.  If you read a lot of his comments, his primary interest seems to be to sell you something.

Go back, on the site to the pages about 60 ish and back and you will see what I mean.