First time posting.....
I own an 81 corvette that was in pretty rough shape. Been spending all my money and time getting it back up to par and now i've run into a problem with the carburetor.
Let's start at the beginning. It was running fine with just a slight kickdown problem but it idled great and ran decent.
My mechanic informed me that the four barrels weren't opening he suggested a rebuild but he didn't want to do it. I found a differant mechanic/friend that was more then happy to do it..... come to find out my quadrajet wasn't from an 81, the numbers matched an 80. upon removal found out that the the gasket had a huge hole in it. He rebuilt it in about 2 days. Now the problem comes in.
When we reinstalled it we can't get it adjusted. To get it to idle we have to turn the it up to around 1500 -1600 rpms anything lower and it sputters and dies.
Also noticed that we had it running at around 1000 and as soon as we put the air cleaner back on it shot back up to 1600.
The mechanic that didn't do the rebuild says it's running rich. (You can smell the fuel in the exhaust)
I can only assume that it was the rebuild since it was running fine before even with a bad gasket. On the plus side the 4 barrels now open.
Any input would be helpful.

 

OK, lets back up a bit. The 81 came with a E4ME Electronic carb, the 80 had a regular carb.
Does your car have the CCC system, computer, distributor and carb on it?
Take a few pics and post em up, we will help you get it sorted out.

 

Welcome to the forum. Sounds like another excellent tech lesson coming from Lars on the QJ.

 

it's set up for mechanical carb

 

Here comes some helpful input.

Judging from your description, it sounds like it's running LEAN, not rich. Putting the air cleaner on (air restriction) removed air from the equation and made it run richer.

You can smell fuel when you have a lean miss - the miss will cause unburnt mixture to be pumped directly into the exhaust system rather than process it.

I'd start with finding a better carb shop to go to.

What do you mean by "the 4 barrels open now"?

 

the four barrels would not open before the rebuild, they were not seized they just would not open when you accelerated

 

How can you tell they're opening now?

A q-jet has two systems to control secondary opening.

One is the choke lockout. This prevents the secondary throttle blades from opening. Once the choke is disengaged, the secondary linkage is fully mechanical, not a vacuum secondary like some Holleys/Edelbrocks.

Second, is the secondary air valves. This has a vacuum component and a mechanical component. The vacuum component is part of the choke pull off system, and this is designed to dampen secondary door engagement/disengagement on shifts. Think of it as a shock absorber for sudden load changes. The mechanical component is spring tension, found on the passenger side of the carb. This controls the amount of load(vacuum) required to open the doors. Many mechanics foolishly think that the doors not opening are a sign of reduced performance. They unwind/remove the door tension so that the doors will open up with no load. This will create a bog condition, as now you have more flow available than what the engine can support and air-speeds drop considerably. The car will eventually recover and start to feel powerful again. Most people confuse this as "the secondaries kicking in".

You should NOT feel the secondaries kick in. It should be a smooth delivery of power from start to finish.

 

so are you saying that the spring tension on the secondaries may be what's causing it not to idle at a lower rpm?

 

No - I was trying to hone in on how you knew the 4 barrels were working.

I'd imagine that the thing is running lean, could be a float set ridiculously low, or jetting/rods that are too far out of spec. If the mechanic merely thought it was rich, he could well have made it even leaner by trying to compensate for it.

Did he use a vacuum gauge to set your idle, a smog machine, wideband, or a hunch? Hunches aren't always right.

Q-Jets are tricky beasts. I had mine rebuilt twice before I got something satisfactory, and even that is not good enough. I'm pretty sure I have a secondary valve tension issue as well. I'm postponing my own experiments on that front until after my transmission swap project is complete.

 

think he used a vacuum tester on it. i will try to post this evening after i talk to the rebuild guy and my mechanic so i can get all the answers

 

Losing my mind. Now that I think of it, these are classic symptoms of a massive vacuum leak.

Could be he used the wrong gasket at the base, air horn, main body->throttle blades or else where. Could be an open vacuum line. Try capping all the vacuum connections and see if that has an effect on the idle. At that point, if it's still bad, start spraying around the gaskets w/ carb cleaner to try to find the leak. Could even be a warped main body, bad throttle shaft bushings, etc.

 

OK. First, the secondaries not opening has nothing to do with rebuilding the carb...it has to do with the adjustments on the carb. So, it's possible that your carb did not need rebuilding, only adjustment.

As mentioned, there is a secondary 'lockout' lever. That is engaged (so the secondaries can't come in) prior to the choke being released. So, properly adjusting the choke usually resolves a choke/lockout problem.

As far as what your buddy did so that the carb which was running well is now NOT running well....you'll have to ask him.

 

K this is what i found out. The secondaries were wired shut. The linkage to the secondaries is missing so they open but they just flop open. He did check for leaks with Carb cleaner and found none.

 

So it had a bad gasket originally as i have posted it had a huge chunk missing. So now that the Carb has been rebuilt and the leak fixed it runs worse

 

It has to be in the Carb right? If it had a leak before and ran fine , rebuild the Carb and fix the leak and now u can't get the idle down that means it has to be the rebuild right?

 

Linkage to the secondaries... the air valves or the throttle blades?

Right now, you'd be better off locking the air valves shut to try to figure out your current idle issue. Those need to be functional for a QJet to work as designed.

Here is a really good video of how the air-valve setup works:


You can see as the truck accelerates the valve opens more and more. When the shift is completed, the air valves relax.

 

Seems likely, but make sure to isolate the vacuum fittings by capping all the ports on the carb and testing again.

There's a chance he hooked something up wrong, forgot to hook something up, or in the process of removal damaged a hose (not necessarily his fault, these things are likely old and brittle!).

 

How the heck do i post a pic from my phone on here? And i think it to the throttle blade. The linkage would be on the driver side clearly visible near the top of the Carb
It's still at the mechanics and not in front of me at the moment but i snapped some pics earlier

 

I think there are some help forums with that. There is no throttle linkage on the driver's side TOP of the carb. The passenger side top will have choke linkage. Driver's side, the secondary throttle linkage is low, near the base plate.

 

I sent my q-jet off my '81 which is a ECM controlled carb to All-American Carbs in Florida. They re-manufactured the carb, came back like new and did not have to change any settings once back on...just perfect out of the box. Cost for me was $300 for work and I paid shipping to and from which was $20 each way. Best deal I've found and the work was perfect. They are on the web, just search them out if interested. Will use them again and again if needed.