so i have to admit this is a ford question. the wife drive a '71 bronco. i am her live in mechanic of course. so i tuned it up when it started running poorly a couple weeks ago. new plugs, cap and rotor. didn't help. so then new fuel filter. still not it. today it got a new fuel pump and i blew out al the lines and made sure that the tank senders (2 tanks) were clear. still didn't do it... so i rebuilt the carb.

this is a fairly stock 302. it does have a msd ready to run dist. and a blaster 2 coil, but otherwise stock. has always run perfect up till now.
in the process of rebuilding the carb, i went as far as taking the throttle plates out and removing the throttle shaft. i did this out of curiosity since i felt some movement in the shaft. sure enough, the throttle shaft is pretty well worn on both ends where it goes through the carb body as well as in the center between the baldes. this is a 2 bbl carb.

the problem is it idles erratically. acts like a vac leak... i replaced all gaskets and checked all possible leak potential areas. now it did increase idle speed when i sprayed some quick start fluid around the throttle shaft on either side.

the thing that baffles me is that it runs fine for a while and then either hunts around up and down in rpm or just starts to kinda bog down and slowly die.

plugs look good... timing is spot on.

so is it time to buy a new carb? there are no bushings or seals on the shaft, so nothing to replace to fix it. i thought about putting some rtv (i know... shadetree to the max) around the shaft to see if it helps. doubt it though.

oh and by the way, sorry about the ford questions, but ya'll always are on your game around here... the bronco forum i frequent amazes me at the lack of knowlege or bad advice i see sometimes

The throttle shafts do wear out and will leak air - Holley has a bushing kit for theirs for this reason IIRC.

Unless you really need that exact carb, I'd just go for a new version of it.

But I'm not sure how to tell if that is really the core problem, as what you're describing could still be debris somewhere in the carb, too.

yeah, the throttle shaft is pretty worn. i would say about .030 worn at both ends of the shaft where it passes through the carb body. quite a bit of movement. also like i said, the idle speed goes up about 400rpm when i give it a squirt of quickstart around the shaft.

replacement is kinda what i was thinking. I don't think they sell a new motorcraft 2100 (direct replacement) so i guess i will have to figure out what is an equal aftermarket replacment. I am a holley guy, so that would be the route i would go i think.

Those 2brl carbs are a simple design that are easy to rbld so go to your local napa/autozone/pep boys etc and get a stock repl rblt carb that correct for your application and you should be fine.

That way everything with fit correctly and it will have a warrentee too.

If it were a more complicated carb like a q-jet i would NOT rec a genaric rblt carb but for a simple 2 brl you should be fine with a general rebuilder carb.

Scott

Those 2brl carbs are a simple design that are easy to rbld so go to your local napa/autozone/pep boys etc and get a stock repl rblt carb that correct for your application and you should be fine.

That way everything with fit correctly and it will have a warrentee too.

If it were a more complicated carb like a q-jet i would NOT rec a genaric rblt carb but for a simple 2 brl you should be fine and they should rebush the throttle shaft if needed too.

If you decied to try a store rblt carb take it out of the box to make sure & wiggle the throttle shaft on the new/rblt carb to ensure its still tight or has been rebushed prior to buying it so you dont end up with the same issue.

Or find a used carb at your local bone yard with a good tight throttle shaft & hosuing and swap that assembly over to the new carb if you have the time to play arround like that and it may save you a few $ too .

Scott

You may have more than one problem. Worn throttle shaft will definitely cause unstable idle, but other than some leanout, not too much effect when the engine is making some RPM. Replace the carb, you may get lucky and that's all you need.

Those 2brl carbs are a simple design that are easy to rbld so go to your local napa/autozone/pep boys etc and get a stock repl rblt carb that correct for your application and you should be fine.

That way everything with fit correctly and it will have a warrentee too.

If it were a more complicated carb like a q-jet i would NOT rec a genaric rblt carb but for a simple 2 brl you should be fine and they should rebush the throttle shaft if needed too.

If you decied to try a store rblt carb take it out of the box to make sure & wiggle the throttle shaft on the new/rblt carb to ensure its still tight or has been rebushed prior to buying it so you dont end up with the same issue.

Or find a used carb at your local bone yard with a good tight throttle shaft & hosuing and swap that assembly over to the new carb if you have the time to play arround like that and it may save you a few $ too .

Scott

You may have more than one problem. Worn throttle shaft will definitely cause unstable idle, but other than some leanout, not too much effect when the engine is making some RPM. Replace the carb, you may get lucky and that's all you need.

as soon as i am off idle, it runs fine. it just acts like a bad vac leak idling. i am military stationed in turkey, so the boneyard is no option for me. not like i can find a bunch of old fords around here. may be able to make a fiat carb work... not.

I am leary of doing the re-conditioned carb. they are just rebuilt used carbs too. so what is to say that it will be any better than the one i just rebuilt. i just rebuilt this one, and i have rebuilt plenty carbs in my time, so i am sure that i did everything right.

like i said, i am a holley guy. i am leaning toward a new holley 2bbl replacement. so i will have to work out some linkage issues and maybe a fuel line... not a big deal. any carb guru's out there know what is a holley equivalent of a motorcraft 2100?