worn throttle shaft?

[Bronchopper]

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.

not sure, but i think it is a motorcraft carb. the rebuild kit said pn. motorcraft 2100 D.

 

[67PONY]

now it did increase idle speed when i sprayed some quick start fluid around the throttle shaft on either side.

That would indicate to me that it is indeed leaking around the shaft.

Do you have a vacuum gauge that you could use to do some quick vacuum analysis to see how steady it is?

 

[justinoshea]

I had a similar issue, could not pass emissions. spray some carb cleaner at the shaft and see if the idle falls. if it leaks the carb is junk. the only carb i got to work good was EFI. good luck

 

[Bronchopper]

That would indicate to me that it is indeed leaking around the shaft.

Do you have a vacuum gauge that you could use to do some quick vacuum analysis to see how steady it is?

yeah, with the movement that is there and the fact that i pulled the shaft and there is at least .030 wear on both ends and a good amount in the middle as well, coupled with the fact that the idle goes up quite a bit with a shot of quickstart to EITHER end of the shaft, i am sure it is sucking air at the shaft/carb body interface.

it runs fine once i am off idle, just idles badly like a big vac leak. i checked all other possible vac. leak sources. they are good to go.

so any good suggestions for a replacement carb? i don't want to get a re-manufactured one for fear of another worn throttle shaft and no better carb than what i have now. i am a holley guy, so a new holley replacement sounds like the route i am going with this.

 

[Jonboy69]

I am interested in carb choices too. Sorry to hijack but a similar issue with mine. My stock Autolite has developed a case of spraying gas all over the motor compartment lately. The guy I just bought the truck from replaced all the gaskets when it was leaking out the front of carb in a couple of spots & it ran pretty good but a little rough. He said the jets may be a little bit big. Today I take it for a spin and come to a stop & it is just coughing & sputtering at idle, try to drive again & has no power then dies. Try to restart but no luck. Opened the hood & it had & was dumping a crapload of gas out the back. Now I am thinking that I just want to go get a new/rebuilt stock carb. A few years ago I put a rebuilt (by Holly) motorcraft 2150 on my 1973 & it worked great. I have a manual choke too & I think I would like to do a electric choke if not too tough to install.

Any thoughts on carb choice ? I want to stay pretty stock as I just use the truck to cruise around town mostly.

 

[broncnaz]

A most of the replacement / rebuilt carbs will have the throttle shaft rebushed making them as good as new. Id go the reman route as the aftermarket route will endup costing you more. Just check the throttle shaft on the carb before you buy it.
You pretty much out of luck as trying to fix it dont put rtv or anything else on the throttle shaft RTV doesnt like gas much and theres always the possiblity of it geting sucked in and causing the shaft to bind or stick not a good idea.

 

[Bronchopper]

A most of the replacement / rebuilt carbs will have the throttle shaft rebushed making them as good as new. Id go the reman route as the aftermarket route will endup costing you more. Just check the throttle shaft on the carb before you buy it.
You pretty much out of luck as trying to fix it dont put rtv or anything else on the throttle shaft RTV doesnt like gas much and theres always the possiblity of it geting sucked in and causing the shaft to bind or stick not a good idea.

i did not know that about the re-man carbs. i guess i might have to try that. i was just afraid that since i am going to do this over the internet (like i said, i am stationed in Turkey, so can't go to the local auto parts store and pick one up) so i will not be able to try the wiggle test first. might be able to get pops to go pick one up for me. I was just kinda joking about the RTV. if it were my driver i could live with it for a while like it is, but since it is the wife's truck, i am stuck listening to her complain when it does not run perfect. thanks for the advice.

jonboy, sounds like you just need to adjust the float level on yours. if your float is set too high, it will slosh fuel out the vents, stumble and flood and run poorly in general. wish mine were that simple a fix. try that before you buy a new carb.

 

[Jonboy69]

Thanks Broncochopper. After it poured out the other day & I attempted to restart it, I believe it popped/backfired back through the carb & may have blown out the power valve. I looked at it tonight and it looks like it may be leaking there at the gasket. Can I just change out this gasket and be all good after adjusting the float leverl ?

 

[Bronchopper]

well, just to bring this post back from the dead. Guess i was right. i got the remanufactured carb from summitt (holley reman'd version of my original carb) model # 64-5336. now don't get me wrong. i am no slouch at rebuilding carbs. i have rebuilt a ton of different carbs (motorcraft, holley, quadrajet's etc.) over the years with outstanding results. that is why this one baffled me. the second time i rebuilt it i paid careful attention to everything since it was still not right after a recent rebuild. it still ran like crap. i noticed during that rebuild that there was quite a bit of slop in the throttle shaft. not much i could do about that. well when i pulled that carb to replace it i also noticed there was gas running out of both sides of the throttle shaft that i didn't notice before. guess the cleaning during the last rebuild let it leak there. anyway, the re-man carb did the trick. truck runs PERFECT now. better than ever. choke works right too. can't beat that. that and a new fuel filter did the trick. the fuel filt was not the problem because it was new when i was having the problem. anyway, here's a couple pics. check out how nasty this fuel filter was from only about 2 months of using this crappy turkish gas! I am actually running a clear plastic filter and the one that screws into the front of the carb. I guess that is a good thing now that i see this!!

 

[Chief Master Sergeant]

I'm glad you got this issue fixed. I had to have mine professionally rebuilt, as my rebuilds sucked. ;D Getting parts overseas sucks.