Trns83

My Quadrajet carb on my 83TA (with a 350 Chev and TH350 trans with 2500rpm stall) has recently started getting "stuck".

When I start up, it revs up quite highly to over 3000rpm and then slowly descends.

When driving, sometimes it hold the revs after throttle and I have to brake to reduce the revs.

I had a look at what the carby is physically doing, and the part that turns when applying the throttle (excuse my lack of knowledge) isn't turning back.

There are two linkages, a spring and the throttle cable.

What do you think is the problem? Is it the linkages or perhaps a vacuum issue? From my understanding there is a vacuum from the transmission to the carby?

Vader

Likely a throttle linkace problem or throttle shaft bindnig. You may also want to check the choke/high idle cam for free movement.

Sonix

iTrader: (1)

I had a similar issue before, turns out the secondary throttle tang was bent a bit, so that when I went into the secondaries, they wouldn't close on their own, so it'd hold the rpm up about 1k or so, until I blipped the throttle and it snapped back, or I hand turned it shut. Just had to rebend the tang.

the part that turns when applying throttle can be called the throttle arm, or linkage...

I definately think it's a linkage issue of some sort. Does the throttle return have a dual spring?

Trns83

Sonix, I thought it would be to answer your question with a picture (attached). I have highlighted a part which looks suspect, this may be what your eluding to. Perhaps I need to tighten this? (if so how is it done?)

Would lubricating any of these parts (with carb cleaner spary) help at all?

five7kid

iTrader: (14)

No, what he's talking about is on the other side of the carb.

Sonix

iTrader: (1)

five7, you've confused me, what are you talking about? referring to me?

I had a problem with the yellow circle area. That rod pointing upwards was bent a bit too far backwards. Probably not your problem here, but thought i'd mention it.

The area you should look at is with the green arrow. That's your primary throttle linkage.

the thing you circled I think is the cruise control slider dealy. Maybe someone can confirm/deny this, but I think I remember removing that....

the linkages aren't meant to be lubricated, as oil/grease whatever, just tends to attract dust, and act like a liquid sandpaper, roughing up the moving parts. Carb cleaner wouldn't lubricate it, but would clean it, maybe you could try that. Most are brass, and have nice bearing surfaces on them, just need to be clean.

You can try a squirt of wd-40 though.

five7kid

iTrader: (14)

Ah, gotcha. Now I know what you were talking about (I thought it was the lock-out tang).

Damon

9 times outta 10 the problem is what Vader said- worn out throttle shaft bushings. GM liked to have the throttle cable and the return spring both pulling in the same direction (backwards) on the QJet. Nice for a clean, space-efficient design, but hell on throttle shaft bushings. A simple switch of the throttle return spring to the top of the throttle arm (not the bottom, like stock) going FORWARD to a spring bracket can often eliminate 80% of all throttle shaft wear on a Qjet. It can even eliminate the problem you are having now, even if your throttle shaft bushings are already shot.

Problems:

1. Not mucdh room around the stock air cleaner to have the spring up top/in front of the throttle arm.

2. No bracket to attach it to up front- have to make one yourself.

99Hawk120

Absolutely--I've noticed that most chevy carbs have worn out throttle shafts, while most Buick and Olds carbs I've worked with tend not to. Those have a bracket as part of the ILC assembly which the spring mounts to. Won't do you much good if you have a Chevy throttle shaft, though, as I don't think there's any place on the arm to attach the spring.

That's reasonably easy to solve; start combing the junkyard for a buick/olds to steal the ILC off of. I've seen ILCs just like the chevy (electric), vacuum controlled, and even brackets which go where the ILC goes but don't do anything but hold the return spring.