My father-in-law just gave us his 1981 corvette with only 80,000 miles on it. It is bone stock other than the catalytic converter being removed 20 years ago! He said he has had carb issues with it since the early 90's and even had the stock one rebuilt in '95. Anyway, this thing runs terrible, just like I've read in several forums . In neutral, runs fine, put a load on it or let it get warm, it limps at best. I do live in Ohio and have no emission testing to contend with, so I'd like to remove all the emissions parts and swap the carb, intake, and distributor. Anybody willing to give some advice or directions on how to do this?

Thank You!
-Jared

 

It would be much cheaper to make what you have run right. There's nothing wrong with the stock set-up on these cars as long as everything is there and working. If the car is as complete as you say, it would be ashame to deflower her. IMO, fix what you have.
Others will way in and you WILL get both sides of the fence.

 

boatdoc is right, it'll likely be cheaper to fix what you have. The only catch here is that the 81's running correctly, only put out about 190hp. I think this is what prompts most people to go after the "smog" stuff in the first place. The problem isn't really the smog stuff though. These engines weren't designed to make big hp numbers. The heads, cam intake, compression ratio and so on were designed for emissions more than anything.

All that being said, a stock 81 running well is a nice daily driver. It's smooth, fun and it'll get you a speeding ticket if you really want one. If you want more hp, your talking about a cam (heads if you can) and intake, modify the existing carb or a replacment, distributor (the stock one is computer controlled) and headers and true duals if you don't have them already. Then if you're doing this on top of an 80,000 mile bottom end, you should seriously consider rebuilding it too. It's really not as easy as bolting on a new intake, carb and distributor, and it's really less expensive to get it running correctly in stock trim...

 

I also have an 81 and just went through what you are experiencing.

http://forums.corvetteforum.com/c3-t...ustration.html

I found that to do what you want, the easiest way would be to buy a rebuilt M4ME quadrajet carb (the same as what you have without computer control) and an HEI distributor. If you go with a different carb and intake you can run into hood clearance issues with no real increase in power. I have been told that the intake on these is actually pretty good. I don't know what your skill level is, but swapping the carb and dizzy is not difficult if you are comfortable with tuning a carb and orienting and setting timing on the dizzy.

That being said, I decided not to go that route. The ECM will throw error codes that can be used to diagnose problems. If you can get a shop manual it has some very good troubleshooting charts. My ECM would not generate the error codes so I replaced it, and in doing so the other problem I was having went away and I have a great running car. In looking at the cost of $400 or more for a new carb and dizzy for no performance improvement I decided against it. We have 190hp cars and, short of doing the mods that damoroso mentioned, that is all they will be.

 

I really appreciate the feedback. I guess I made up my mind to junk the factory stuff because it ran so poorly and my father-in-law said it has for some time. I know this thing is far from a race car and I really just want something I can fire up and drive or my wife can take my son for a drive without worrying about limping it back home. I priced the Edelbrock 1406 carb for $299, Edelbrock 2701 intake for $139 and the MSD 8362 Distributor $132.95. I have a friend that is an ASE mechanic that said he'd swap the parts out for FREE but said his days of chasing down issues like the stock problems are over. I don't know, maybe I am just so frustrated because the car looks so nice but runs embarrassingly bad! Oh Ya, it has the "Twin Turbo" hood and an unknown body kit on it.

 

Certainly your call, these aren't hard to troubleshoot if you know what your doing. Could be as easy as a bad O2 sensor or temp sensor. It's worth getting the service manual and checking out the codes. Hell, a replacement computer is less than $100, a carb rebuild is about $75 for the best parts you can get....

 

 

Thanks for the advice. The car does still look very nice but I am afraid to spend too much money chasing the issue??? The problem is, I don't know what I'm doing. However, I did just buy the temp switch today. For $15, I'll put it in and see what I get. A few of the hoses are cut and the cat conv was removed in the 80's! I can't imagine trying to get the O2 out being that its never been changed. I sincerely appreciate all the help and am not against trying to fix it. I did notice that the vacuum switch off the drivers side of the coolant inlet is broke. Will that cause any issues? The check engine light does intermittently come on and off, so it appears to be working. Also, it smells extremely rich and if you hold the choke open, it runs a bit better???????

 

I would recommend a compression check before spending any money..but yes if it checks out you will gain HP and fuel mileage by replacing those items and disabling the 'puter!

 

No worries, but you really ought to consider getting a service manual for the car. You can get one at any of the vette part suppliers and it'll give you everything you need from A/C, engine, transmission and carburetor overhaul directions to info on how to adjust you windows and tops. It's really worth the $100 bucks or so. Plus, it'll walk you through troubleshooting your current issues. As for holding the choke open, these cars have an electric choke and if you don't have power at the choke, it'll never open and that'll cause all kinds of problems like your describing. The O2 sensor will come out, hit it with some PB blaster (or similar) and let is soak for a bit, it'll come out. Yes, the vacuum switch can cause issues, it controls the charcoal canister that's tucked in the drivers side fender. That could be where your fumes are coming from, plus make sure you have the correct gas cap on the car.

Swapping the intake, carb and dizzy MAY increase HP, but not enough to make a real difference. There are three serious limiting factors here. 1) the heads don't breath particularly well, 2) the cam isn't designed for hp, it's designed for emissions, and 3) your lawnmower probably has a higher compression ratio. This engine is running 8.5:1. Unless your running a blower or turbocharger, this isn't really good for making horsepower.

Seriously, I suggest you buy the book, it's a good investment and give it a read before you start buying parts....

 

OK, so several people have chimed in in strong favor of maintaining the factory equipment. Obviously this is a sensitive subject as people are either heavily for or against their choice of parts. But....... I have decided to try to make it work in stock clothing. I replaced the broken ported vacuum switch, plugs, wires, cap/rotor, coolant sensor, fuel filter, and choke thermostat. The pull off is working fine and and I cannot find any vacuum leaks. The check engine light continues to come on and off, but it's actually slightly improved and drivable now. It sill bogs or falls on its face when you get on it. Also bought the o2 sensor and have had no luck in getting the old 1 out. My mechanic is heavily in favor of a trip to out hometown speed shop - Jegs! Not giving up just yet, but I am getting very frustrated with this thing!

 

Hey, this is my first time responding as I am I new member. I too have an '81 with the orginal carp however the computer has been removed. Mine is getting very poor fuel milage (less than 12mpg). What caught my attention is what you said about the fuel cap. Mine has been replaced. Should I replace the gas cap since I know nothing about it? It is a combination locking gas cap. Would I go to the local Chevy dealer or local auto parts store or Corvette speciality store? Thanks.

 

Don't give up trying to make things right. You must have (or develop) a great capacity for patience with these cars that are 30+ years old. Many of the rest of us have been through similar situations and feel your pain but we continue to torment ourselves because we love to keep these old cars so we can continue to drive and enjoy them.
Terry

 

These cars WILL drive you nuts but when the project is done, oh what a feeling!!!!

 

On my '81, i swapped to 600cfm holley carb, carb adapter, taylor HEI distributor, and disabled the computer and it runs great. I also blocked off the egr and removed the air pump and all the mess of vaccuum lines. My engine looks alot cleaner and runs alot better. I should also mention the original carb and distributor were missing when i bought the car and the computer was already disconnected. good luck with yours

 

Jacobs81, how can I tell if my '81 has the original HEI distributor? I know the computer is gone. From matching photo's, I still have the original Rochester. With the computer gone, i guess it would be a bad idea to purchase a new computer provided I still have the original distributor? Thanks in advance.

 

OK, so it's done! And I have to say, I tried all I could to get it running good in stock clothing, but to no avail! Every mechanic I know wouldn't touch it but was willing to assist in the swap. It all went very smoothly, fires right up and purrs like a kitten. The good news for me is that my father in law replaced the TH350c with a non computer controlled TH350 15 years ago. So no issues with the lock up!

 

Id get a Holley carb and a $54 ebay distributor and save some money.

 

You can't just pull the ECM off an '81 C3 and expect the ['81] carb to work properly. The fuel mixture is set by the ECM; if you remove it, the carb reverts to its "default" setting of running very rich. That is what you will have to work with unless you swap the carb out for a pre-81 carb or put the ECM back on the car.