Idle problems with 1980

[king80vette]

My 1980 idles rough and has been this way for as long as I’ve had the car, 3 years now. It runs fine above about 12k RPM. Mechanics and other people have told me it could be a vacuum leak or the carburetor needs to be rebuilt.



It has the L48 engine, auto with 14k miles on it. The stock intake manifold was replaced with an aftermarket non EGR and the air pollution stuff was removed when I got it.



In an effort to fix the problem I have rebuilt the carburetor, replaced the intake manifold with the correct EGR GM one, installed the pollution stuff, replaced vacuum lines, gasket between the carburetor and intake, gas filter, cap, rotor, spark plugs and wires. I think that’s it.



When I was checking numbers I found that the distributor is a high altitude one. And I do not live in a high altitude area. Is there a way to confirm this, maybe on the build sheet? I have the history of the car and it was sold new in this state and has always been in this state. Could this be the wrong distributor for the car and could this cause the problem? The car also runs lean the ceramic on the plugs turn a reddish color. Do you think the carburetor should be re-jetted to give it more gas? If this truly is a high altitude car would the carburetor have been jetted differently then a non high altitude car?



Any help with this problem will be appreciated.



Thanks, Steve

 

[king80vette]

Correction it runs fine above about 1500 not 12k RPM. I don't think it will run good at 12k RPM.

 

[Stallion]

Sounds like it might be timing. Have you had a timing light out on her?

 

[king80vette]

I should have added that the timing is way off. I'm having a hard time getting the timing on the indicator. If I adjust it to get the timing near the indicator it runs so rough it's hard to keep it running. I have been just setting it by ear.



I put the distributor back in the way it came out. Could it be off a few teeth? When adjusting the idle mixture screws how many turns out should I start with?

It could be a combination of bad adjustments.
:confused

 

[wishuwerehere82]

Adjust your idle mixture screws(Needle valves) to 1-3/4 turns initially after you pull them out and shoot some carb cleaner through the passages. Do it a few times until you can see it spraying in the carb throat. Replace the needle valves after cleaning them off.
1) Set the timing
2) Adjust the idle mixture on both sides with a vacuum gauge until you get the highest vacuum at idle or a tachometer to get the highest RPM.
3) Re-adjust the idle speed to 650 RPM.
4) Re-adjust the idle mixture again.

 

[king80vette]

Thanks everyone. I'm going to work on it this weekend.
Steve

 

[Stallion]

Adjust your idle mixture screws(Needle valves) to 1-3/4 turns initially after you pull them out and shoot some carb cleaner through the passages. Do it a few times until you can see it spraying in the carb throat. Replace the needle valves after cleaning them off.
1) Set the timing
2) Adjust the idle mixture on both sides with a vacuum gauge until you get the highest vacuum at idle or a tachometer to get the highest RPM.
3) Re-adjust the idle speed to 650 RPM.
4) Re-adjust the idle mixture again.

But if it was his idle mixture, then wouldn't it be a constant sputter throughout all/most RPMS? Or not...

 

[king80vette]

It still runs rough at idle and I can not turn it below 1000 RPM or it will stall. I can not get the timing set properly because it just runs rougher or stalls as I get closer to 6deg. Could this distributor be the wrong one for my car. At 1000 RPM the vacuum jumps back and forth between 14 & 16 in Hg. Turning the idle mixture screws seams to have little or no affect on the idling.



Steve

 

[wishuwerehere82]

It still sounds like the idle circuit in the carb is clogged solid. They should be smoothing out the dile as you adjust them and the vacuum should vary as the mixture is adjusted.

Timing can be bumped up to around 12 degrees to keep it running.

But, you are going to have to unclog those jets first.

 

[king80vette]

When you say jets you’re talking about the idle mixture screws (Needle valves) correct? I also noticed the choke and idle solenoid are not working. Should they have 12 volts going to them all the time? I'm going to work on it Wednesday night.

Thanks,

Steve

 

[wishuwerehere82]

Yes, there are passages on the carb the run from the float bowls to the needle valves and then go into the carb throat. If those passages are clogged, the gas won't flow and you won't have any control over the idle mixture. That '80 carb has a lot of electronic gobbledygook all over it, and if the idle solonoid is not working, that could be disabling the flow internally, but I am not too familiar with it.
Have you considered a replacement?

 

[king80vette]

I think if I can't get it working this week I will look into a replacment.

Steve

 

[wishuwerehere82]

As best as I understand.

The high idle solonoid should be engaged when the engine is cold or when the A/C is on. The choke should be engaged at startup until the engine comes up to operating temperature, and the temperature sensor in the air cleaner throat turns it off.

 

[wishuwerehere82]

You should be able to get a rebuild kit for it with step by step instructions for rebuild included. Here's one from NAPA.http://www.napaonline.com/cgi-bin/ncommerce3/ExecMacro/NAPAonline/search_results_jt.d2w/report?pcc_ids=1435&acc_pcc_ids=&ENG=44%7C5.7+L+350+CID+V8&ENG_FUEL_DELIV=11%7C4+Barrel+Carburetor&search_string=&org_string=&considered_txt=PC

 

[wishuwerehere82]

http://www.napaonline.com/cgi-bin/ncommerce3/ExecMacro/NAPAonline/search_results_jt.d2w/report?pcc_ids=1435&acc_pcc_ids=&ENG=44%7C5.7+L+350+CID+V8&ENG_FUEL_DELIV=11%7C4+Barrel+Carburetor&search_string=&org_string=&considered_txt=PC

 

[wishuwerehere82]

Sorry, the full link isn't copying down all the information.

 

[smithjw]

I had a similar problem this spring on my 81. I did most of the things that you have already tried. My problem turned out to be the fuel pump. I took it off the car and found that it had a small nail in it which was blocking the passage in the pump at idle speed, but overcame the blockage at higher rpm's. I have no idea how the nail got into the fuel pump, but upon installing the new pump, there was a trick needed to get the push rod up high enough to get it inserted into the pump. I think the previous owner had already replaced the pump once and used a small nail to prop the push rod up. After getting it inserted, I think the nail fell into the pump as well. I used a different trick to keep the push rod up when I did the install by backing out a bolt and replacing with a longer length bolt that would reach the push rod and keep it pinned up. Anyway, the new fuel pump solved the problem.

 

[brusso]

I should have added that the timing is way off. I'm having a hard time getting the timing on the indicator. If I adjust it to get the timing near the indicator it runs so rough it's hard to keep it running. I have been just setting it by ear.



I put the distributor back in the way it came out. Could it be off a few teeth? When adjusting the idle mixture screws how many turns out should I start with?

It could be a combination of bad adjustments.
:confused

May need to replace the harmonic balancer. (The thing that has the timing mark on it) Sometimes the rubber rots and the outer ring can shift. It's a two piece item that is bound together by rubber.

 

[king80vette]

These are good ideas that I will have to look into. I did not think of either one of these things.

Thanks,

Steve

 

[king80vette]

I finely go my car fixed today. The problem was the screws going up through the carburetor from the bottom were loose. After making them tight and reinstalling everything the engine idled smooth. I was then able to adjust the idle mixture screws and the idle RPM’s. Then the timing could be set properly. The vacuum is now at 19 inHg and it is running better then ever.