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Off Your Carburetor - Dirt-Tuning the Motorcraft 2100

Posted in How To: Engine on July 3, 2013
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One of our favorite rules of engineering is the KISS rule. Keep it simple, stupid. Simple things that work and work well are often taken for granted, but without them you’d be in trouble…or at least not as able to have fun with your Jeep on a given weekend. One such item that angers us when it does not work properly is the carburetor. Many may argue that a simple fuel injection system is the best fuel-delivery system for a Jeep, and while that may be true, fuel injection is generally not cheap. Carburetors are cheap, and chances are your older Jeep came with a carburetor—so you’ve already got one. Over the years, we have paid attention when people have told us what things have worked for them. Here are a few simple and easy modifications that you can do to your carburetor to get it to work better off-road. We are mainly gonna focus on the Motorcraft 2100 two-barrel that was available on mid-to-late ’70s Jeeps, as well as on many Ford cars and trucks. This carburetor is a great place to start, as they are relatively easy to find used, are easy to rebuild, and are relatively easy to get parts for. They also have a pretty good reputation off-road when adjusted properly and have been adapted to several Jeep engines. We talked to a couple of friends who have been running Motorcraft 2100s for several years on their Jeeps. Shane Thompson has been running a 2100 on a well-built Buick 225 odd-fire in his ’67 CJ-5, and Brennan Metcalf has been toying with the 2100 that feeds the 225 odd-fire that powers his ’42 Willys MB. Both carbs are on odd-fire V-6s, but 2100s are also great carburetors for AMC V-8s (many of which came from the factory with a 2100 or 2150) and can be easily adapted to feed the 258 I-6 and others.

You want to find a Motorcraft 2100 carburetor from a small V-8 or inline six-cylinder for your Buick V-6, 258, or smaller V-8. You want the 1.08-inch venturi size; the venturi size is embossed on the driver side of the carburetor body. Common sizes are 1.08 and 1.21—others are 1.14 and 1.02. Some of the earlier Motorcraft 2100s share jets with Holley carburetors, making tuning easier and less expensive. Having the right size venturis, jets, a good rebuild, and proper tuning will make or break the 2100’s function. Oh, and pesky vacuum leaks—those too. Initial tuning should start at 11⁄2 to 2 turns out on the idle mixture screws.
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Brennan’s 2100 Sidehill Baffle Trick
Brennan has tried several tricks to optimize his 2100 carbs function for off-road. One modification he made to help carb idle steadily while negotiating extreme sidehills was to build a new top gasket leaving the area over the bowl solid gasket material. He then made a hole with a .45 caliber shell casing in the solid gasket maker on the driver side and used a lathe to machine a plug for the vent on the driver-side top plate of the carburetor. He then left the passenger side vent hole in the top plate open, but added a restricted riser to the passenger side vent. We’d probably just make the new gasket and plug the driver-side vent. The idea is that this creates a baffle system in the carb so that when the Jeep is leaned to one side or another, wet fuel won’t pour out of the vents.

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