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Rebuild Autolite 2100/4100 CarburetorsFrom the January, 2012 issue of Mustang Monthly By Mark Houlahan Photography by Mark Houlahan
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To remove the carburetor from... To remove the carburetor from the intake manifold, there are several connection points to separate the carburetor from the engine. First up is the throttle linkage. On the early mechanical linkage setup, Ford used a spring-loaded retaining clip. Pry it off of the linkage rod and slip the rod out of the clip and throttle shaft arm. In this day and age of electronic fuel injection, we find it strangely comforting when we walk up to a vintage Mustang at a show or cruise-in and see the age-old mechanical fuel mixer sitting atop the engine's intake manifold. Unfortunately, the old hot rod adage of "bigger is always better" often rules the day when it comes to carburetion (and camshafts, and exhaust, and valve size, and so on!). We regularly see mild 289ci and 302ci small-block Fords wearing 650-750 four-barrel carburetors, all in the name of more performance. However, a carburetor of that size is usually just wasting fuel and giving you poor fuel economy. Ford spends billions of dollars on engineering their cars with parts designed to work right and last, so we find it ironic when people remove a perfectly well-engineered part to put a lesser quality part in its place. This goes for vintage as well as newer Mustangs. To that end, many people think the original Autolite carburetors fitted to '60s Mustangs are "factory junk" that need replacing with aftermarket carburetors (that usually require a different intake manifold, throttle linkages, PCV connections, and more). In reality, the Autolite 2100 2V and 4100 4V carburetors are well-engineered and thought out pieces that often just need some TLC and service parts to make them factory fresh once again. On 1966 and later Autolite... On 1966 and later Autolite carburetors, the fuel filter threads into the main body. Disconnect the fuel line to the filter. We'll be replacing the fuel hose and clamps during the rebuild. If your Mustang is missing its Autolite carburetor, you can find usable cores at most swap meets or online, then simply go through the carburetor with a good rebuild kit, replace any fittings/linkages required, and setup the carburetor's adjustments for fast idle, choke, accelerator pump shot, and more to have an accurate and well-running carburetor that fits, looks the part, and runs efficiently. If you're looking for a more concours solution, there are several companies, such as Pony Carburetors, where you can have your carburetor professionally rebuilt and tuned, including show quality plating, or simply buy the proper carburetor outright. The carburetor we're going to crack open here is an older Pony Carburetors-built 4100 4V. The plating and finish are still in great shape, but due to lack of use and today's E10 fuels, the carburetor has started to leak and give starting and driving issues. So follow along as we take our aging 4100 from crusty leaker back to a show-ready atomizer that runs right.  The four carburetor retaining...  The four carburetor retaining nuts are removed using a 7/16-inch socket or wrench. Note the position of the throttle return spring bracket before removing the driver's side rear retaining nut.  On applications that use a...  On applications that use a hard line for the distributor vacuum source, you will need to loosen the pinch nut at the base of the carburetor and pull the line out. Access is easier if you remove the choke heat shield. Lastly, disconnect the hot air choke tubes, if equipped.  With the carburetor removed...  With the carburetor removed from the intake, find a suitable work surface where you can spread out the disassembled parts. We usually rebuild a carburetor on an old t-shirt or towel to prevent parts from rolling off the table. Remove the carburetor's air horn retaining screws and set them aside. If your carburetor still has an ID tag on it, take care to prevent damaging it.  With the air horn screws removed,...  With the air horn screws removed, the choke plate rod retainer is removed using fine needle nose pliers. The air horn can now be carefully separated from the main body and set aside.  Disconnect the float hinge...  Disconnect the float hinge pin retainer from the fuel inlet seat and carefully remove the float and needle assembly, followed by the inlet seat. This is the primary fuel bowl (front) shown here. If you choose to remove the main metering jets, be sure to note their size and locations in the main body.  Unscrew the primary booster...  Unscrew the primary booster venturi retaining screw and carefully pull the booster assembly free of the main body. Note on the primary side only there is a weight and check ball for the accelerator pump discharge. Carefully remove these as well.  As you disassemble the carburetor,...  As you disassemble the carburetor, it is best to lay the parts out in order of removal so you don't mix up screw lengths or linkages. For the four-barrel 4100, we also made sure to keep primary and secondary hardware separate as well.  Remove the four screws securing...  Remove the four screws securing the accelerator pump cover and then remove the diaphragm, spring, and elastomer valve from the main body. We left our accelerator pump linkage connected to the main throttle shaft for now.  The choke housing on the Autolite...  The choke housing on the Autolite 2100/4100 is removable. First remove the three screws and steel retainer holding the choke cap in place, then remove the three longer screws holding the choke housing to the main body.  Invert the main body and remove...  Invert the main body and remove the four screws retaining the power valve cover and gasket, then remove the power valve with a 1-inch boxed end wrench or socket.  While the main body is still...  While the main body is still inverted, the idle mixture screws can be easily removed. If your carburetor ran fine and you're just rebuilding it due to leaks, take a note of which screw you are removing and begin by carefully turning the mixture screw in (clockwise) until the screw seats, counting the turns, then remove it. Repeat for the other mixture screw. Be sure to write the number of turns down so you can return them to the same settings.  For you 4100 owners, the vacuum...  For you 4100 owners, the vacuum secondary diaphragm is not included in the rebuild kit. You can gamble that it is okay, but if your 4100 has not been rebuilt in several years, the diaphragm will most likely look like ours, so go ahead and order one with your rebuild parts. Don't forget the check ball in the passage at the top of the secondary diaphragm housing if equipped.  Now that you have a bare main...  Now that you have a bare main body (there's usually little need to remove the actual throttle plates and shafts), give the main body and its passages a good cleaning. You can either soak in a solvent bath or use canned carburetor cleaner. Just be sure to clean all passages and blow them out with compressed air. Check all gasket surfaces for debris and clean with a razor blade as needed.  Once you've verified that...  Once you've verified that all passages are clean and you can feel air through them, the main body can be assembled with new service parts, starting with a new power valve and housing gasket. Our rebuild kit is from National Parts Depot and includes all necessary gaskets, needle and seat assemblies, power valve, and small parts. If your Autolite needs a replacement anti-stall dashpot, secondary diaphragm, or other small parts, they can set you up.  The kit's fuel inlet seat...  The kit's fuel inlet seat is installed, followed by the inlet needle and float assembly. Following the rebuilt kit's instructions, the float level is checked and adjusted to spec. The secondary float is shown here, but the primary float setting is adjusted the same way.  Before installing the primary...  Before installing the primary venturi booster, don't forget to slip a new check ball and the original weight back into the center hole. Follow with a new venturi gasket and screw (with a new gasket under the head), then tighten the assembly, being careful that the booster venturi seats properly. Repeat for the secondary booster venturi (minus the check ball and weight).  When reinstalling the choke...  When reinstalling the choke housing, the small gasket on the lower leg is often missed (those exploded view diagrams are tough on the old eyes!). Insert the attaching screw, as shown, to hold the gasket in place and carefully assemble the choke housing to the main body.  The choke cap can be a little...  The choke cap can be a little frustrating because you have to engage the choke's thermal spring on the thermostat's lever link and piston assembly. You'll know you have it when you can rotate the cap and feel the spring tension. Secure the cap (don't forget the gasket) with the original choke cap retainer and screws and set the choke per the rebuild kit's instructions (two rich for our carburetor).  The air horn gasket is laid...  The air horn gasket is laid onto the main body followed by the air horn itself. Be careful of the vacuum tube for the secondary diaphragm passage on the 4100s. You don't want to get it caught or hit/bend it. Tighten all of the air horn screws evenly.  NPD sells Motorcraft service...  NPD sells Motorcraft service replacement fuel filters like this Motorcraft FG-15. It might not pass concours judging, but it certainly will function and fit the application.  To keep our '66 Mustang as...  To keep our '66 Mustang as correct as possible, we opted to use new concours fuel line and clamps from NPD. If you read our Mustang tools story last month, then you surely ran right out and grabbed a pair of these crimp clamp pliers. The fuel line kit includes enough hose and clamps to do the whole car, not just the fuel filter.  If you rebuilt your Autolite...  If you rebuilt your Autolite because it was running poorly, then you'll need to seat the idle mixture screws (gently) and then turn them counterclockwise one to one and half turns as a baseline. With the engine at operating temperature and the idle speed set, attach a vacuum gauge to the engine. Turn the idle mixture screws evenly to obtain the highest vacuum reading possible on the gauge while maintaining the proper idle speed.  Your Mustang's carburetor...  Your Mustang's carburetor needs clean fuel and clean air to operate properly. We've already replaced the fuel filter while rebuilding the carburetor, so it goes without saying that a new air filter is a given with our rebuild. NPD has stock paper filters, the correct Hi-Po open element filter (shown here), and even K&N direct replacement performance filters. The choice is yours.  While we don't have the room...  While we don't have the room in this rebuild story, and frankly carburetor identification is a whole story onto itself, we did want to mention the Ford Carburetor Guide from Pony Carburetors. This pocket guide is a useful tool when looking for the right carburetor for you vintage Mustang. Full details include venturi sizes, ID tag info, caveats, and more.
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