I have an '81 still equipped with the computerized carb. The car has only 40k miles so it has sat more than it has been driven. The problem is that if I floor the gas the back barrels won't open. It doesn't bog or hesitate, but they just won't open or at least I don't hear the roar that the Quadrajet is known for. It idles great and runs great other than that.
Any ideas?

 

The E4ME carb will give performance equal to other Quadrajets, but the engine has to call for it. The exhaust on the L81 is very restrictive to begin with, and if the cat is clogged, or the header is rusted out where the primary pipes come together (or both), the car may just not have enough umph to give that Quadrajet rush.

There are a few other things you can check though:

1. Check that the secondary rod lifter cam is functioning.

2. Be sure the secondary lockout disengages.

3. Be sure your throttle linkage is unobstructed.

Here is how to check all three:

With the engine fully warmed and OFF, take the air cleaner off and open the secondary air valve (the butterfly on top of the secondaries). You should see it lift the secondary rod hanger (the wishbone that mounts right between the secondary bores).

Next, while still holding the air valve open, have someone press the accelerator fully to the floor. You should see the secondary throttle plates (the butterflies at the bottom of the secondary bores) open fully.

If they do not open at all, the secondary lockout from the choke is probably maladjusted and is engaging the pin on the passenger side of the secondary throttle shaft.

If they do not fully open, look down the primary bores and be sure your primary throttles are fully open.

If the primary throttles are fully open, your linkage needs adjustment.

If neither the primary nor secondary throttle plates are fully open, you may have something obstructing you gas pedal (carpet under the pedal in a wad, etc.)

God bless, Sensei

 

Remember that the secondaries are vacuum and not mechanical. They are only opened when there is sufficient load. You probably won't generate the load if you're reving it in park (or it will only open a little).

My guess is that as long as you can open the secondaries by pressing on the butterflys and as long as you are not experiencing any symptoms, they are working fine.

Unfortunately, stock 81s don't roar

 

Thanks for your responses!! I will check these things when i get home today.

CA-Legal, are you saying that the '81's don't have the sound as the older Q-jets or that it just doesn't run as hard as the older ones? I know it doesn't run real hard(quick-fast-etc). I was just going by the sound of the carb. comparing it to the ones "back in the day" when I would tromp the pedal just to hear the carb.

 

Sorry for the delay, I missed your response.

I was saying that the 190 HP will only make so much roar. Still sounds better than a Honda Civic, but I don't think you can expect it to sound like a big block with side pipes.

 

I had the same computer carb on my 81 Z28, and it did make the Q-Jet roar you refer to, so I would think yours would too.

 

are all Q-Jets vacuum...I have an '84 Q-Jet on my '77 - i thought it was mechanical??? How can you tell?

 

Heard that. Unless you clean out the catalytic converter. Then they come a helluva lot closer to roaring.

 

This is a common misunderstanding. All Quadrajets have mechanical secondaries. What that means is, with the engine off (no vacuum), the secondary throttle plates will open when you press the accelerator pedal.

Where the confusion comes in is that the Quadrajet has a secondary air valve that is controlled by vacuum. It basically makes the Quadrajet a variable CFM carb. This is why an 800 CFM Quadrajet can give the crisp throttle response of a 500-600 CFM carb, but still deliver the performance of an 800 CFM carb.

People complain about the complexity of a Quadrajet, but it is that complexity that gives it advantages like this over "simple" carbs. This is why I say, for a street driven machine, a Quadrajet is the only carb to have.

God bless, Sensei

 

Verify that the secondary throttle plates will open completely when someone depresses the accel pedal [in the car]. Throttle adjustment, carpet thickness, etc. can limit throttle linkage travel. Also, there are adjustments on the carb to prevent the secondary plates from opening if operating conditions are not 'appropriate'. Choke adjustments and vacuum can operation are critical for allowing the release of the secondary lock-out lever. Info can be found in the Chevrolet Chassis Service Manual on carb adjustments.