My '78 with a completely stock L-48 and a Quadrajet has trouble idling.

It idles sometimes but it takes forever.

I just completed installing a new exhaust and took it for a ride around the block but it still won't idle.

When I backed into my garage I blew my radiator hose. I don't know if the hose blew because of the high idle or just a weak hose.

I just got the car a few weeks ago and my first project was the exhaust system.

I was told that the carb was rebuilt. I bought it from a performance shop that did all the work so I believe him.

Anyway it idles very very high. When I take the air cleaner off and close the butterfly it calms down but idles up when I let go.

I've checked the vacuum hoses and everything seems to be connected and I've sprayed carb cleaner on the linkages.

I don't think it's the idle adjustment screw because it has kicked down a few times.

I'm new to Quadrajets and all these vacuum lines.

I have a feeling this is a common problem so I'm hoping someone can help me with this.

Hoses won't blow because it revs too high right?

Any change the PO put a auto carb on a 4 speed car? And would that make a difference?

 

What do you consider too high of an idle? Give us some numbers.

Welcome to the club. Don't let this discourage you.

 

Thank you. Since I blew a radiator hose I can't start it up again.

I believe it was around 3 grand.

 

The choke linkage, fast idle links, pull off, and thermostat are all on the right side of the carb. I'd look at the link from the thermostat to the carb, make sure it's not hanging up and that all of the fast idle cam is not sticking.

 

First thing you do is isolate the problem, meaning disconnect the throttle linkage. Then you will know if its the carb or new carpet hanging up the gas pedal. It happens.

 

No carpet at all yet. It's not the linkage because it does kick down. It just takes forever.

 

There is no heat stove on the manifold. There is no hose connected off of the snorkel that would normally connect to the heat stove. Could this be the issue?

 

It would be great if yiou can take a good clear photo of the passenger side of the carb where the choke assembly is located....and also let us know if you still have a heat riser on the exhaust.

The heat riser is controlled by a TVS ( temperature vacuum switch) that is in the intake and will cause the heat riser to open and allow exhaust to get out once the water temp gets hot enough to cause the heat riser to move. If you heat riser is always open...your choke will take forever to heat up and get the choke to pull off.

SO...If you do have a heat riser and the vacuum pod that attaches to the heat riser that moves the flap in the heat riser...take a photo of that also or at least clearly describe what you have.

If you have no heat riser...it will take a long time for the choke to pull off....because you carb does not have an electric choke.

Do you know how to manually get the choke to pull off by pushing down on the linkage on the passenger side??????

DUB

 

I can take a picture tomorrow night. The heat riser has been removed by the PO.

I do not know how to get the choke off as you describe.

How important is the heat riser? Would that fix the idle problem? Should I put one back in?

 

You got Dub's attention! He is one of the best around here and always willing to help. Answer his questions and you will be on a good path.

 

I will wait and see what you have going on.

No problem...when I see what you have going on..I will post a photo of where for you to push on the carb to get the choke to go off....unless someone else posts photos and shows you.

A functional heat riser is very important if you are having a choke
operation issue.

Yes..it possibly can..because if the high idle setting is correct ( about 1500-1600 RPMS)...but your choke is not pulling off...then the engine will always be at high idle.

This may be possible...but will have to wait and see what you have missing. Or possibly converting to an electric choke...which can lead to other issues in trying to make sure the air cleaner base fit correctly.

DUB

 

Thank you so much DUB. I'm wondering if it's a vacuum issue. I don't know the name of it but the choke thing on the back of the carb doesn't have a hose attached to it. There is also a hose coming off of the back of the carb that I had attached to the air cleaner. You can see it in the pictures. I'm not sure if that's where it goes or not.

 

But the idle comes down sometimes. It has idled. But it took a very long time.

 

It is not clear in your pictures if you have a cam installed on the choke assembly intermediate shaft. The red arrow on my picture shows the cam. Maybe you don't need it due to the second vacuum pull off on the rear of your carb?

 

'Norcoasatal'

Thanks for all for the GOOD photos. They were a really good help. And also THANKS to 'bmotojoe' for posting a photo of where to push down to get your choke to go off and idle.

NOW....I think this is not the correct carb due to I ahve never seen a Corvette of your year model with that other pull off on the right side rear of the carb.

Can you post the carburetor number???

Below are images on where to look for the carb number and they might be lightly stamped in the main body so take your time when you are looking at it.





I can say that I now need to see the heat riser or at least the exhaust on the right side...especially where the exhaust pipe attaches to the exhaust manifold. It may be possible that IF you still have a heat riser..it may be able to be controlled with a cable....OR....

Possibly take off the choke on that carb and install an electric one.

I know why it takes so long for the choke to finally pull off and you have an idle... and that is because I can see that you do not have either two of the temperature vacuum switches in your intake/thermostat housing. One of them if for your EFE system..which is what allows this type of choke design to function. Which is why I really need to see what you have going on a the exhaust on the right side.

DUB

 

Hi DUB and thank you.

I took off the air cleaner to replace the radiator hose just now and while I did, I put the vacuum hose that wasnt connected to anything to the vacuum choke diaphragm. I also sprayed the carb on the choke side with carb cleaner. I also pushed down on the choke cam.

When it started up it didnt immediately go to choke mode. It actually started at normal pace and settled in with a really nice slow idle. It's a little rough, but not bad at all. I think it's running rich because it smells like it and my wife is complaining that the whole house smells like exhaust.

The history of the car is that I bought it from performance shop. The shop said that it had a stroker motor in it and he bought it just for the stroker motor; but the original matching numbers motor was on the floor beside the car.

Since he was a performance shop, he sold the stroker and put the original in the car. He went through (checked) the bottom end, rebuilt the heads with a new valve job and installed the motor back in the car. He said that it didn't have a carb so he built a carb from a bunch of parts that he had lying around.

So the carb is a frankencarb. There is NO heat riser on the passenger side between the manifold and the exhaust pipe. There is a spacer where the riser went.

I'm thinking that maybe I need a new carb. I wonder if someone on this forum has a carb that belongs on this motor?

 

I wonder if someone on this forum has a carb that belongs on this motor?

We know your car is a L48, is it auto or manual transmission? A/C or no A/C?
There are several numbers used in 1978 depending on options.

I think you posted it's a 4 speed car correct?

 

Yes it's a 4 speed with no AC.

 

If it's running rich, is it as simple as turning that dial towards "lean"?

 

The correct number carburetor for your car is 17058203.
The running rich condition could be a number of things. The frankencarb does not help things.
Sorry I can't be of more help.