Rebuilding Autolite 4100 Carbs





There are a few things to look at prior to even trying to rebuild the carb. One of the major problems with this carb is throttle plate wear. If the throttle shafts are loose in the throttle plate, it is no use rebuilding the carb till you remove the shafts, have the outer holes bored and refitted with bushings at a machine shop. Vacuum loss by the throttle shafts is the number one cause of poor 4100 performance. This usually rears it's ugly head in the form of poor idleing and off idle bog due to the fact that you have to set the idle mixture screws wrong to compensate, and also because the butterflys are positioned, at idle, such that when you step on the gas, they pass the idle transfer port at the wrong time relative to engine rpm. Many compensate for this by adjusting the positioning of the accelerator pump rod in the holes at both the pump lever end and at the throttle lever end. Bottom line, all you are doing is masking the real problem with quick tweeks. It ain't gonna work!

Ok, now that the throttle plate assembly is either good or fixed, you need to remove and replace the needle and seats for the float valves. These must be replaced. They get old, they leak, they cause flooding. Next thing is to disassemble the
accelerator pump on the front of the carb. the screw on top holds in the check ball (a ball bearing) which MUST be installed or you get poor pump discharge. Also, the big spring between the pump diaphram and the carb body must be in place or the thing will not pump. Remove the cylindrical rod that the pump rod actually presses against. This is generally a little hard to get out, but with a little coaxing it comes out. The kit chould have a new one. These babies like to stick when they get old. This causes a lower then normal pump shot and the classic hesitation on acceleration.

Below the accelerator pump, you will see another small housing with 4 screws. This exposes the power valve. It is VERY important to replace this! These love to go bad, and if your car has ever backfired, chances are this could be damaged.
Anyway, this little devil can cause poor acceleration as well as flooding. The big thing to remember here is to install that thick gasket on the valve then screw it back into the carb. If you forget that thick washer like gasket, you will have a very
very rich running engine, that is if you can even keep it running!

The only other stinker is the primary booster venturi assembly. It comes off with one screw, but when it comes off, if you tip the carb over, a rod and a ball bearing will fall out. The ball bearing goes in that center hole forst followed by the rod.
If you forget these, your car will run, but it can and most probably will scavange fuel from the accelerator pump jets causing it to run rich at speed, have poor fuel economy, and foul the plugs.

Cleanliness is next to Godliness when working with carbs. If you do not use a whole can of "Gumout" on this baby, you are not cleaning it enough! Do this OUTSIDE if you value your lungs and brain cells.

The secondaries are much simpler. The secondary booster venturi assembly comes off with one screw, just like the primary, but does not have the rod and ball since it does not have an accelerator pump system. On the back of the carb is the vacuum diaphram assembly which is generally good, but, if it is bad, you will have to remove it and replace the diaphram assembly. The diaphram is both the vacuum diaphram and gasket all in one. The headache is that the actuator lever for the secondary throttle shaft must be removed, and you will have to drive out the pin in the carb housing that
it pivots on.

Do the rebuild one step at a time. Do NOT disassemble the carb into a hunderd parts and think you are going to get it all back together without forgeting where some key piece goes.

Adjustments will need to be made to get the thing to run right. Initially, set the idle mixture screws out 1.5 turns. Next, set the floats per the specs for your particular year dry.
Now, install the carb on the car, crank it till it starts and shut it off. Remove the fuel line! You do NOT want any pressure to the fuel inlet of the carb at this time. Remove all the screws on the top AND the big stud that the air cleaner attaches
to so you can remove the airhorn assembly. Now do your final float level check for both the primary and secondaries 'wet'. Make any necessary adjustments and you should be set to go. The service manual for the 61 and 62 Tbird has a section on the carb. It offers a lot more information then you will ever get in a rebuild kit's sheet. If you have the service manual, review the section on the carburetor. This will really help a lot!