I have had the car in the garage for the last couple months working on some minor projects. Before sitting, the engine would idle nicely at about 750 rpm when warm. I took her out today, and it was running at about 2,000 rpm. It would settle down to about 1600 rpm with a mash of the accelerator.

I gave it plenty of time to warm up, so it shouldn't be the choke, should it? The fast idle choke setting wasn't ever set as high as 2,000 rpm, anyway.

I have an Edelbrock 600cfm carburetor. I know very little about adjusting it, but did attempt to adjust the idle speed screw. Usually I can change the idle rpm with that. Backing the screw off (to lower the rpm's) didn't do anything. The throttle linkage was such that I could advance the idle speed screw to raise the rpm's, but when I backed the screw off, none of the throttle linkage followed- ie, the rpm's would not drop.

Any help? What am I missing?

Thanks,

Matt

 

Vacuum leak?

 

OK, this is a possibility. One of those "minor projects" is listed in another post as "vacuum leak in ac control."

I had been having a leak in that area, and disassembled the control valve to investigate. I may not have put it back together correctly. Could this cause that big of a difference in performance?

Thanks,
Matt

 

Not sure. Block all the ports that are irrelevant to engine performance and see if it goes away. If you are fairly sure the A/C is a major culprit, disconnect it and block it with your finger to see if the idle drops.

-Steve

 

Matt: My 79 has an A/C soleniod that kicks up the idle when the A/C is turned on. Could that be your problem? The soleniod is about 1" in diameter and about 2" long. It is located almost underneath my carb and has a single wire running to it. The wire can be disconnected from the soleniod if you really need to. :smash:

 

Assuming it is the electric choke - when warm, hold the throttle open slightly and pull the primary choke plate fully open. This will tell you if the fast idle it hanging up. The fast idle linkage and adjusting screw is most likely on the drivers side below the throttle idle speed screw. You want to make sure the fast idle is not hung up and make sure the primary and seconday throttle plates are not hung open too much. If you backed the idle screw all the way down and idle is still up toward 2000, you have something mechanical hanging up, need to find it.

Vacuum leak, put a gauge on manifold vacuum and see what you have. Stock 350 at 2000 should be running around 18-20". If low, one at a time plug each vacuum takeoff from the carb and the intake manifold and see if the idles down.

 

It is definitely the fast idle linkage.

After warming it up, the engine still ran at about 1500 rpm. I was able to manipulate the linkage. The rpm's dropped down to 800. I then opened the throttle/ depressed the gase pedal, and the the idle rpm would reset to 1500. It continuously catches at the fast idle.

How do I fix this? Does it need cleaning? Lubing?

Thanks!

Matt :crazy:

 

I have an Edelbrock 600cfm carb also. I just came in from the garage. I haven started my vette in nearly a week. Here is what happend:

I opened hood and removed the air cleaner.

Snapped throtle to close choke plate. (When doing so gas is squirted into the primaries)

Turned the key and it fired up. (My fast idle was at 2300rpm)

Snapped throttle a second time and the rpm dropped to 1300 while watching the choke plate to ensure the electric choke is functioning properly (choke plate was slowly opening)

Once opened (choke plate) snapped throttle a third time and idle dropped to 600rpm (nice idle) All of this took place in a span of less than two minutes.

With a cold engine, remove the air cleaner to check if the electric choke (assuming carb has one) is functioning properly.

Snap the throttle, this closes the choke plate (same as pressing accelerator)
Start engine. Snap throttle again, rpms will drop and watch the choke plate until it is fully open. Once open, snap throttle and the rpms should dropto the idle speed you have set.

Remember thefast idle cam will disengage once the choke plate is FULLY OPEN. Give this a try and let me know what happpens.

Of course one would not remove the air cleaner when starting vehicle to be driven. I suggested doing so you can see and understand what is happening once the engine is started. Once this is done, check for vacuum leaks, etc and make necessary corrections/adjustments.

On edelbrock's web page there is a printed copy of a carb manual which explains how the fast idle screw should be set.





[Modified by Oldguard 7, 12:22 AM 3/13/2004]


[Modified by Oldguard 7, 12:25 AM 3/13/2004]


[Modified by Oldguard 7, 12:29 AM 3/13/2004]

 

Saw the last post on blipping the throttle when warm and it goes down to 800 and but then if you open it up it goes back to 1500. Your choke setting is too rich and is causing the fast idle cam to engage when ever you open the throttle. When the engine is fully warm the choke plate on the primary must be 100% open. If not, adjuist the choke cover a notch or two leaner so it is open fully. I am pretty sure you said you have an electric choke. 1) check for 12vdc on the choke. If not - troubleshoot back. 2) if 12vdc is the choke housing warm or hot? If cold, you have an open element. Sert your meter to ohm's and see what it says across the ground to +12 terminal (with +12 dicsonnected. It should be almost continuity of 0 ohms. If not, you have an open element.

If you have the manifold heat spring or divorced type the spring is probably shot.

 

Nice call, I found the problem. As usual, it was self-induced. :rolleyes:

The choke plate was not opening as the engine warmed up. I tried adjusting the choke as shown in the manual. This didn't do anything, either. Hmmm....
I wonder if it's getting power? I checked, and it wasn't. Followed the wire back through the firewall, and found it loose on the other side.

While working on those "other projects," I had inadvertently disconnected the wire to the choke. It's hanging loose near the fuse box on the driver's side kick panel. The problem is... I can't figure out where to reconnect it. Anybody know where my choke wire should go after coming through the firewall?

Thanks,

Matt

 

Well done Matt,
The wire can be connected to any source of +12vdc that is "hot" oly when the ignition key is on. Since you seem to have it tied into or around the fuse panel, take the meter and find a source only when the key is on. Or - if you have the +12vdc line that was feeding the throttle solenoid that is hot only when the key is on. Tie in there or run a wire from that source to the choke. Good luck and when you have the hot line to the choke adjust the choke for a leaner or less spring tension for this time of the year. Several notches to the left of center should be ok. If it still runs on choke too long in warmer weather, go one more notch. That way you are not dumping raw gas into the engine on warm days. Set it back for colder weather.