Carb problem?

[gedmeyer]

OK, got a few questions here. Hopefully not too much.

1) When I start her up cold, she doesn't run at a higher rpm to warm up. She starts up and tries to idle at about 600rpm cold, which doesn't always sound too good. I have to give her a little gas until she smooths out. Is this a choke problem? I also question some of the check valves off the exhuast, does this have merit?

2) I can't get her to spin her tires to save my life (from the line or going to second). I would think that she would have no problem doing this without dropping the clutch from insane rpms? Would this be a function of a out of tune motor or secondaries that aren't opening? It seems like she doesn't run as well when I hit the gas hard. I'd compare to her wanting to take a breath of air that isn't there.

Finally, I am wondering if should pull the carb off and rebuild it while she's sleepign during the winter. Would there be any major benefit to doing this? I would like to get the motor running at her fullest potential. I would probably rebuild myself if I were to do it.

I know this is probably a lot of question asking, I've been reading the forums for a while now, just haven't been posting...

 

[Dave L.]

Welcome gedmeyer! I also have a gray 81 4 speed. Is your engine completlely stock?
If it is I don't think you'd be able to 'spin'your tires even at optimum performance. Our cars have a 2.72 rear gear ratio.,great for highway cruising not good at all off the line acceleration. Those electronic carbs are a little tricky to rebuild. A freind of mine who has alot of expierence with that E4ME type Rochester rebuilt mine and it made it big difference. One of the things you mentioned, when you hit the gas hard and it stumbles is most likely a mixture control solenoid issue. When you turn your key on just before it starts do hear a clicking sound coming from the carb? You should. Thats your mixture control solenoid. It would be a good place to start getting your carb rebuilt to solve
the problems you're having. If you are going to do it yourself,get the 1981 GM shop manual first,it goes into great detail about repair of the E4ME carb.
Got any pictures to post of your car? My car has the camel interior,how about yours.

happy motoring...Dave

 

[atmmac]

sounds like accelerator pump and choke problem i would recommend rebuilding.

 

[gedmeyer]

I've never posted a pic before, so hopefully this works...

I don't recall hearing a "humming", but I'll have to check next time I get a chance. Are there any "good" carb rebuild kits that you would recommend? I know ours is a little different because it's computer controlled.

How does the smog and exhaust recirculation fit into the scheme of things? I am wondering if I'm losing any efficiency through worn out components. I have a fair understanding of most things under the hood, but other than knowing it's purpose, I do not know what the AIR system connects to.

 

[Tom Bryant]

Bud's will spin the tires in the dirt. Don't ask me how I know. (I'm still sorry Bud).

As Burglar said you are going to have to get a copy of the ST-304-81 Chevrolet Shop Manual. If your choke isn't closing properly when cold and pulling up the fast idle cam there are several adjustments that may need to be made. The manual shows these on pages 6C4-12 and 13 with diagrams that are worth way more than 1000 words. If you rebuild your carb following the manual to the letter and making all of the adjustments it should run great.

One of the most important adjustments on a Q Jet is the secondary air valve preload. If the spring tension is set too light the valve will fall open too soon and you will get bogg. If it's too tight then you will have delayed opening.

After you have done all of the adjustments from the manual take the car out where you can play without getting in trouble. With the engine warm start with the spring tension a tad tighter than the factory setting in case the old spring is getting weak.

Proceedure:
1) loosen the lock screw with a hex key.

2) Turn the tension screw counter clockwise until the air valve starts to open.

3) Turn the screw back clockwise until the valve just closes then turn it 1 full turn further.

4) Lock it with the set screw.

Make a full throttle rolling start and accellerate through 1st gear. It whould feel like you need more air. Loosen the valve preload tension spring screw 1/8 turn at a time, making a full throttle pass after each adjustment, until you hear and feel a little bogg start to set in. Then tighten it back up 1/8 turn. The valve preload should now be optimized and your secondaries should come in right on que.

You might want to run through all of these external adjustments before you pull the carb for rebuild. You may be very happy with it after it is adjusted right. Also make sure your ignition and wires, plugs, timing, EGR, fuel filter and air cleaner are right before you start twisting on the carb.

What is your concern about the check valves on the exhaust? Are you talking about the ones on the A.I.R. tubes?

Tom

 

[gedmeyer]

Hey thanks a ton, that was a big help. I guess I have to get that shop manual. I've been following them on Ebay trying to avoid the 80 bucks, but I'm not sure if that's gonna really be worth my time. I think I'm gonna have to wait until the springtime before I go through that procedure because the insurance rolls over on her on Oct 9, so she's in the garage hibernating after that. More than likely, I will do a carb rebuild over the winter to ensure that everything is up to snuff. In the spring, I plan on doing new plugs/wires too.

My concern with the AIR system is more of a question I suppose. I wasn't sure if it could creat and leaks or blockages that would effect engine performance to any degree of severity.

 

[Tom Bryant]

No. It just blows air into the exhaust manifolds to complete the burn of unburnt fuel exiting the port.

 

[mikejpss]

gedmeyer- here's a different perspective:
Junk your old computer controlled carb and buy a new (professionally) rebuilt one . The downside is you'll have to replace the distributor too, with a vacuum advance one. This will bypass all the computer functions. I did this earlier this year and have yet to regret it. My original carb was shot, even after rebuilding so my choices were narrowed quite a bit.
also, been looking for an excuse to post a pick of my lil baby, so heres one :
b/t/way- if anyone needs an original computer controlled q-jet, shoot me an email. My old one is just sitting on a shelf and would be glad to help out another 81 owner. Caution: the carb is xtra ugly!
my 81 with a new paint:

 

[Dave L.]

Mike...beautiful looking car!

Dave

 

[chockey]

gedmeyer
I was having similiar problems and considered a new carb, but a mechanic talked me into a partial tear down to see what was the problem and found gasket problems. With the gasket replacement and adjustments it ran 200% better, no hesitation, no fast idle and I'm very happy. I also put a K&N air filter in her, total cost $70, now she has some kick when I step on it, big difference.

Chuck

 

[gedmeyer]

I don't think I can get put a new carb on it. For 2 reasons, cost being one and other is originality. I've still yet to come to grips on my overall vision for the car (stock vs going for performance and what not.) I feel like I paid for a stock car and I'm worried about destroying any relative value that it had.

So I think rebuilding is the best option right now. Anybody know of a good source for rebuild kits?

 

[AUSSIEVETTEMAN]

I agree with mikejpss!

gedmeyer,

If you could afford a new carb, my suggestion would be to change your dizzy and purchase an Edelbrock Qradrajet carb (1903).
It is an exact copy of your old faithful there! Looks eactly the same only with an Edelbrock tag, which can be removed!
Only difference is that it doesn't hook up with the ECM.
All the other vacuum lines, fuel line and other bits just fit right on.
My girl has a Mallory MSD ignition and Blaster 3 Coil. You could of course, see if they have a copy of the old HEI dizzy, as I know they sell a coil that sits on the dizzy like the original.

I had a Holley 650 Double Pumper on my car when I purchased her in April this year.
It did the same as yours does now, coughing and spluttering in the morning and had a major flat spot and would not pull the crust of a rice pudding!
To get her to leave rubber, I had to pull the hand brake on!
We tried everthing, including changing the power valve and the jets. Nothing.

The solution was a Quadrajet Carb.
I searched the net and found some prices (around $440 US) and then did a search on Ebay. Yep, there was a new one there!
Managed to pick it up for $330 US, which by the the time it landed here in Oz, was around $1080.00 Oz.
Best dam decision we made!
Touch the gas and away she goes. No tyres left if you don't want them anymore, she actually runs like a small block Chevy now.
Problem I think was the Holley didn't have the air flow needed to make HP and the overfueling caused a big flatspot.
I have not changed the air cleaner housing, it is stock as is everthing except the dizzy.

Food for thought!

Cheers

Tony

 

[mikejpss]

Another alternative is the Jet Performance Co.'s rebuilt Rochester Q-Jet without the computer hardware. This is the one I chose & am very happy with it. It is a reconditioned carb with all new stuff sunk into it. You can find it at their website, or at Jegs.com. Mine is a stage 1 which was $359 shipping included. It was actually cheaper at Jegs then going thru the Jet Performance Co.'s web page/phone order line.
It was a perfect match with all attachment hook-ups (vacuum lines,throttle linkage, etc), less the computer plug-ins.
Am tickled pink with mine, but I have not tried to smoke the tires with it either. Mike J.

 

[gedmeyer]

I think I'll try to work with what I already have (including the computer) and see if I can get some better results. I am still real hesitant about swapping out original parts to put in aftermarket stuff. I would have bought a cheaper vette in need of work if I was going to replace everything in it.

I appreciate the advice, but I think doing a rebuild myself will be the best way to go. The carb is by no means toast. Freshening up is all it needs.

 

[Dave L.]

gedmeyer- Go with a kit from GM. I'll post the part #'s you'll need when I get to work in the morning. Carb kit, float and a filter will fix you up. I would stick with the stock setup also. When properly adjusted,the stock carb and distributor will work fine. I see no need to go spend $300-600 when its not necessary.

Take care...Dave

 

[mikejpss]

gedmeyer-
best of luck on the rebuild job. If you find that you may need parts from another carb, remember I got one on the shelf you can have, just let me know and I'll ship it to ya!
It has a new rebuild kit in it to boot.
Let us know how it comes out.

Burglar- thanx for the compliment on my new paint job- needless to say I'm kinda excited about it. When I get finished with the interior we'll put up some more pics.
later, Mike J.

 

[gedmeyer]

hey thanks guys, you've been a tremendous help in sorting this out!

happy driving

-tim
aka gedmeyer

 

[chockey]

Tim
I see you are in upstate NY, just curious where. There is a club in the Ithaca Area (Generations Corvette Club) and in the Binghamton Area (Southern Tier Corvette Club) and another one in Elmira area but I don't know the name.

Again, I'm really glad that I had new gaskets, intake manifold and another on the carb. With adjusting it runs like a top and still its original.

Chuck

 

[gedmeyer]

chockey, I'm 15 min north of Albany, so all of those clubs are along ways away. There is one in Glens Falls (about 35 min from me) that I might join... I really would like to see some other peoples '81's just so I can have some comparison... If you ever decided to head east my way, I'd be glad to hook up at some point.

 

[Dave L.]

carb kit GM# 17076043
float GM# 17067445
filter GM# 5651803

Dave