I have a stock Rochester Quadrajet. I haven't done anything with this carb in the 20 years I've had the car and its now starting to have issues that I believe its the carb.

Stumbling when I start, little to know starting power, smell of gas if I punch it. I know I could use a rebuild but figuring maybe its time to just replace it. Remember I live in California so I'm somewhat limited. Also, don't want to dump a bunch of cash on this so looking for something resasoable.

Let me know your thougths.

Thanks

 

ECM works?

 

How about sending it off to someone who'd competent in rebuilding them (Lars?)?? I'm guessing cheaper than buying a new one, and a lot less screwing around.

/

 

OP has not told us if the 'first-ever' Corvette ECM system on his car is operational....or not.....

 

What is ECM

 

That would be "Electronic Control Module".
the computer thingy that tells your car how to run and in some cases how to shift.

 

I don’t think Lars works on ecm controlled quadrajets. FYI.

 

The 1981 is an ECM-controlled carb, and cannot be swapped out for anything else if you intend to pass emissions. I don't do any ECM carb work, but Henry Olsen may be able to assist on that one.

Lars

 

I've seen guys on online searches who sell rebuilt carbs, they seem to have a thorough checklist, incl 81's. I don't have any personal recommendations.

 

My thought is that if I ever bought an 81' Vette, even if it was perfect, it would get a 1978-80 Carb and GM performance pre-curved HEI......the CCC carb and distributor work until they do not and yours is not working due to the idle mixture control solenoid. You can put one in it if you can find one....they are about $100.....but I would take the the opportunity now to change it all out. Bad IMCS will run pig fat......as you are experiencing.

Jebby

 

For what it’s worth, I put a rebuilt carb on my 81 about a year ago. I didn’t have high expectations since it was a eBay purchase. The price was around $350.00 and it works perfectly fine The car has never idle so well, with that being said I did have to tweak it a little. Got lucky I guess.

 

It's in front of the battery and gets input from several sensors, including the throttle position sensor on the carburetor (driver's side electrical connector). It then controls the air-fuel mixture in the carburetor by pulsing two needles in the mixture jets (passenger side electrical connector).

The factory manual is very easy to follow, and you don't need any special tools other than a volt-ohm meter and the ability to read the flashing codes from the check engine light. For me the hardest part was locating the test connector under the ashtray and inserting a screwdriver in the correct slot to tell the ECM to flash the codes.

Any old-school mechanic can rebuild your carburetor, but it has t be tuned on the car as part of that process, and that requires connecting and reading a volt meter. Lots of guys get all in a tizzy with that last part, but it's really no big deal. The only caveat here is that in order to adjust the throttle position sensor the rebuilder will need to drill out an aluminum plug that prevents monkeys from playing with the tiny adjustment set screw. That's not unlike the idle mixture screws (which are also plugged by the factory). Then use blue Locktite to keep the screw from backing out.

Lots of guys will tell you to just toss it and go mechanical but the other thing that the computer does for you is adjust the advance on the distributor. It also locks up the torque converter. Since you have the misfortune to live in The PRC you will also need it for the emissions functions. Since I happily live in a state that respects my freedom and my old cars I was able to remove most of that junk that tends to make the engine run poorly and pollute more.

The easiest way to check to see if the ECU is working is to unplug the four-wire connector to the distributor. Set your timing at 6 degrees BTDC and then reconnect it while the engine is running. It should advance the distributor quite a bit, off the factory scale. Then do the same thing to the carburetor. Remove the passenger side electrical connector, start the engine and listen to the carburetor. Reconnect it while the engine is running and you should be able to hear a faint but steady clicking sound, several times per second, which are the mixture needles bouncing up and down.

My ECU was burned out when I got my car. When that happens the carb runs full rich, and then that clogs the single catalytic convertor. I diagnosed my ECU fail through the factory manual. A rebuilt one took a day to get to me, over the counter at Autozone for $82.

 

If it's a stock driver, the easiest thing is to just get the carb rebuilt or put a rebuild one on it. 81's that are computer controlled run and idle smooth. They'll idle smooth all day long b/c the idle is computer-controlled. That is ...when everything works fine. And when things don't work fine, it's usually not that hard to figure out the problem (if you take it to the 'right' guy, or take the time to learn the system).

 

The idle speed is set by a screw...

 

...Constantly monitored and adjusted by a MC Solenoid.

 

My fear on these 81's is that the wiring now is 39 years old. I was replacing GM ECM's and PROM's and ICS's and CCC Distributors 30 years ago.......about one in one hundred GM ECU's will take a ****, now add 39 year old wiring to the mix and it is a losing proposition.......
Now I know that 20 people on here have 81's that run fine......it is when it doesn't.....one year only distributor and carb that is almost unobtainium would make me swap this stuff out before it quits. It is not because the 81' didn't run right new.....it just has almost zero support, is not conducive to ANY upgrades short headers/exhaust...maybe an intake....and the distributor curve map is pathetic.
In the case of the OP's car.....you can stick a Idle Control Solenoid in it but the chances that it will quit again are high....they are not an easy part to find anymore and most are "rebuilt".
I am one of those "right guys" that you could take your car to.....and I say fix it if you want......but change it all out if you can.

Jebby

 

The system has OBD-I diagnostics built in. If the ECU is functional, it will guide you to the problem; with the fault-tree info in the GM Service Manual for 1981, it can also lead you to the wiring or the ECU, if they are the fault. If the system is NOT operational, it is up to the owner to decide to stay with the early '81 electronic control system or replace ALL of it with a system of the 'past' or with a system of the 'present day'.

From my point of view, if the car has not been in a flood or a fire which could do major damage to wiring and electronic items, 40+ year old wiring should be deemed 'serviceable' until it is found not to be so or if it can't pass simple visual inspection judgement. Those who just pull out wiring because it is OLD could be wasting their money, if the wiring isn't presenting any obvious problems. If someone is doing a complete restoration and they choose to replace wiring and electrical items at the same time, that is certainly appropriate action. IMO, discarding functional items which are not exhibiting problems is likely a waste of time and money. I would not discard any 'factory' parts for today's reproductions for ANY REASON other than significant part wear, damage, malfunction or safety risk. Just being OLD doesn't fall into any of those categories/

 

Sorry, I'm with Jebby. I'd pull it out and put in an earlier carb, distributor. Or, change it out to a more modern EFI setup.
but hey, I'm running EFI on my 77. And yes it runs great. And if it takes a **** in 10 years. I'll bet there will be an even better system to replace it with.
40 year old wiring, 40 year old computer controlled carb?
certainly there is a better fix.
Just my honest opinion.

 

An 81 in Ca. must retain all original smog to comply.
All carb and smog parts are available with exception of diverter valve and EGR control solenoid.
Quadrajetparts.com has all the parts.
DUI has new distributors.
In Ca. you are allowed to upgrade to a newer engine IF you transfer all related smog equipment to the car with the transplant.

 

Or check and see if any local shops near you can repair ( or remember how ) to set up , you can give a decent baseline on the bench but at some point it has to have a final mixture dwell adjustment " on the car " which makes it hard to just send it to somebody for repair