Thank you all for the additional responses! 79 USA 1 mentioned the choke pull-off. I think it was this past Monday, when I had to move the car for street cleaning, I did the usual three steps on the pedal before starting—as advised by the carb guy, then started the engine—it was in fast idle. After about five minutes of letting it warm up, I tapped the pedal to lower the idle, it didn’t lower—tried it again, no change. I shut off the engine, gave a quick, strong tap on the pedal, then re-started, it was in low idle. It gets stuck like that once in awhile. Pretty sure this ain’t right!
Fast Idle Faster!
- Thread starter DWCaprice2017
- Start date
Nope. That's not right. You may have some sticking or misadjusted fast idle. And again, check that choke pull off. Easy to do. Put a vacuum source on the tube going to the front choke pull off. Draw it in, you should see the choke pull off rod be pulled in. Hold it for 10 seconds, and if it holds, great. If it bleeds off, you've got an issue. Some Chevies have a bleed hole in them as I understand it, so put a piece of tape over that bleed hole first. Don't forget to pull it off after the test. God forbid the linkage isn't damaged or whatever. That's another one of those things you can't bench set and leave it that way. You have to adjust all that on a running vehicle. I believe this is going to take some carb finesse to fix, and there's no way to tell you how to finesse your situation over the interwebs. Not very easily, that is.
Sounds like idle hang, where the idle hangs at fast speed not wanting to kick down.
the idle should come down with a tap on the pedal when warmed up the linkage could be hanging up or a week return spring or choke not opening i have even put a spacer on top carbs because the linkages get stuck on the air cleaner ..when you restarted it and it was on low idle did it run good ?
A 1984 has an electric choke, right? I have dealt with poor functioning choke elements before. It must be grounded properly, [no gasket] , and the hot wire must have a good 12 volts. A fresh new element may just solve this. It also may help to remove all the vacuum hoses and plug the fittings just to see if that changes anything. There could be a leak far downstream that you are missing.
As mentioned, choke operation is all open loop. Another thing to check is the choke pull-off. When cold the choke needs to close totally. The first pump of the pedal releases the choke linkage so the choke flap closes and the fast idle cam sets. [It also pumps a squirt of fuel- don't over-do that] There is a spec for the fast idle speed adjusted by the screw in the video. Upon start-up, the vacuum pull-off opens the choke flap to a certain spec. That is measured with a choke flap angle tool that no one has. I go back to the early non-CCC carbs for a spec that is usually between 1/8" and 1/4". That is a good starting point. The rule is that if the engine stalls, too much air, close the flap a bit. If it runs rough, not enough air, open the flap a bit. This is adjusted by the screw on the choke pull-off linkage. Upon start-up it should go to the specified fast idle speed and run smoothly.
As mentioned, choke operation is all open loop. Another thing to check is the choke pull-off. When cold the choke needs to close totally. The first pump of the pedal releases the choke linkage so the choke flap closes and the fast idle cam sets. [It also pumps a squirt of fuel- don't over-do that] There is a spec for the fast idle speed adjusted by the screw in the video. Upon start-up, the vacuum pull-off opens the choke flap to a certain spec. That is measured with a choke flap angle tool that no one has. I go back to the early non-CCC carbs for a spec that is usually between 1/8" and 1/4". That is a good starting point. The rule is that if the engine stalls, too much air, close the flap a bit. If it runs rough, not enough air, open the flap a bit. This is adjusted by the screw on the choke pull-off linkage. Upon start-up it should go to the specified fast idle speed and run smoothly.
On low idle, it runs a bit rough. I'll check the spark plugs, but I doubt that's an issue, they were replaced about two years ago and I barely drive the car--up until this past June, I was driving it about 30 miles a week, for about a year and a half.
The only code checking I did was to connect a paperclip into the two terminals in the diagnostic port--no codes came up. I made sure to watch for the three-repeat of the codes. I ran it twice--key on/engine off. There had been a few times when the Check Engine light came on briefly, but I wonder if the engine was about to stall when that happened. It hasn't come on when I speed it up on Mondays to re-park it.
While that can be several things, start with the easy stuff. Fresh spark plugs, or at least cleaned and gaped plugs. Vacuum leaks. Are you under emissions testing? If not, and the idle mixture plugs are exposed, you can hook up a vacuum gauge and adjust the idle mixture. [A 'rebuilt' carb should not still have the mixture screw plugs in place] They are probably the 'double D' type screw heads. A friend had his cousin come up from Florida with an '84 Monte Carlo SS. It idled like crap. Noticing that the plugs were missing and the screws were 'double D' I used my Snap-On 'double D' adjuster tool to adjust the idle mixture. I had to open the screws quite a bit, but man did she respond! Whoever 'rebuilt' that carb left them super lean and it ran rough as can be. I told him he probably won't pass emissions now, but he said in Florida there is no emissions test. He said after I richened up the mixture it ran better than it ever did.
Thank you for your response!
Yep--California...smog test needed. I went in for a preliminary test, I was told it might/might not pass.
I decided I better increase my odds of passing by getting the engine as good as possible. Yes, I need
to check the spark plugs, but they were replaced about two years ago, and I barely drive the car--when
I was driving it--taking the bus since June. I was putting on maybe 40 miles a week to get to work and
back--I don't think that would be enough to wear out the plugs, unless they were the wrong ones to
begin with.
Yep--California...smog test needed. I went in for a preliminary test, I was told it might/might not pass.
I decided I better increase my odds of passing by getting the engine as good as possible. Yes, I need
to check the spark plugs, but they were replaced about two years ago, and I barely drive the car--when
I was driving it--taking the bus since June. I was putting on maybe 40 miles a week to get to work and
back--I don't think that would be enough to wear out the plugs, unless they were the wrong ones to
begin with.
Idle is the most delicate mixture to get right due to the low airflow. The most common cause of rough idle are vacuum leaks. Did the mechanic check for a worn primary throttle shaft? If its worn it can cause rough idle. Qjets can be rebushed with either brass or homemade Teflon bushings. Also if the idle airbleed valve has bad o rings that can cause a vacuum leak.
With old emissions systems its handy to have a Mityvac to test various components for vacuum leaks. The stock idle needle setting for eQjets is 3 3/4 turns from lightly seated. If your valve stem seals are old they can quickly oil foul your spark plugs.
Moreover, you are blind attempting to work on CCC systems without either a analog dwell meter or a OBD1 scanner. The best method I found for finding vacuum leaks is to wave an unlit propane torch at suspect areas while watching the computer response via a dwell meter. When the leak ingests propane the computer will respond lean, which shows up on the dwell meter. Its actually easier to find vacuum leaks on CCC engines than non CCC because how sensitive the computer is.
With old emissions systems its handy to have a Mityvac to test various components for vacuum leaks. The stock idle needle setting for eQjets is 3 3/4 turns from lightly seated. If your valve stem seals are old they can quickly oil foul your spark plugs.
Moreover, you are blind attempting to work on CCC systems without either a analog dwell meter or a OBD1 scanner. The best method I found for finding vacuum leaks is to wave an unlit propane torch at suspect areas while watching the computer response via a dwell meter. When the leak ingests propane the computer will respond lean, which shows up on the dwell meter. Its actually easier to find vacuum leaks on CCC engines than non CCC because how sensitive the computer is.
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