hello all. i purchased a 66 mustang recently and the carb went bad on me.
i ended up using the carb off the old motor out of my 71 f100 on it and it works
great with only a mod to the throttle arm. ( hole on top in mustang carb for
linkage rod in bottam on truck carb). runs great now but seems to use almost twice the gas. i was wondering if the bore in the jets on the 2100 carb from
the truck is bigger, or any other ideas why this may be. i am assuming the
truck carb is a 2100 . it's the original carb. any answers/advice on this would
be greatly appreciated.

 

The truck carb may very well have bigger jets, but the only way to tell would be to remove the tops of both carbs and compare the jets. The truck carb may also give the engine a bigger squirt of gas from the accelerator pump. It might not hurt to check the plugs to see if the engine is getting the proper air/gas ratio, indicated by a light tan color on the porcelain. This is best done with new plugs. And finally, have you checked for any gas leaks?

 

When was the carb rebuilt? If the carb needs rebuilding and is leaking gas or air, it can easily kill your mileage. My 2150 2bbl was so bad, I went from 6 mpg to 8.5 mpg by putting an adapter on my manifold and bolting on a 4 bbl 600 CFM Holley Street Avenger.

The other thing I would look at is air flow. 66 Mustang is a pretty restricted engine compartment, you might need more air flow for the carb. you bolted on. Did you check the underside of both carbs and make sure the holes for the 2 bbls line up with the holes on the manifold? The 71 probably had an aluminum carb spacer, did you reuse this too?

At any rate, I would put a vacuum guage on it and make sure you are pulling at least 17 and adjust the carb for the engine. If you went from a FE to a 302, I would not be surprised it did not work perfectly without being set up.