I have a 1969 corvette 427 with the 3x2 carbs and I have a sticking idle. The car has a few modifications like a comp cam, MSD non-HEI distributor (The one with the internal module), and roller rockers.

Here's my problem: When I start it up it idles fine but then as soon as you drive it and it goes over roughly 2500 rpm the idle hangs when coming to a stop. It hangs just under 2000 rpm at a dead stop. I tried a few things to fix this (I am new to the 3x2 set ups) I adjusted the air to fuel ratios on both sides of the middle carb, checked timing, made sure the choke was fully open and lubed the linkage as well.

Any fixes to help me resolve this issue would be greatly appreciated.

 

Check the operation of your fast idle cam and make sure it's dropping all the way down when the choke opens.

 

where would that fast idle cam be? Thanks just because I’m new to the carbs

 

Hi Lucus ,its on the passengers side of the middle carb ,just above the coke arm and is green .

 

Is there a throttle return spring on the center carb? I'd completely remove the rods for the end carbs and see if the throttle shafts are sticking and then drive it to see if the problem is still there. Make sure you follow the shop manual procedure for adjusting those rods when reinstalling.

 

DO NOT DRIVE IT WITH THE OUTBOARD RETURN ARMS DISCONNECTED!!!!! Not saying 3X2 said to do it but it reads that way if you dont understand what he meant

Those arms close the outboard carb butterflies. LEaving those arms disconnected invites the carbs to go WOT and stay there. IF you run with he arms disconnected you also run the risk of and arm hanging up on the manifold and not letting the middle carb close. IF you must run with the arms disconnected unplug the vacuum hoses going to the outboard diaphragms and plug the hoses.

THere are multiple problems that could be the issue provided you have everything set up correctly and have a return spring on the center carb. Check fort the obvious like sticking choke and choke high idle like Lars said. Make sure your throttle cable is loose at idle. If all that is fine its usually a vacuum leak. CHeck for lose manifold bolts and carb studs. Carb studs do not need to be over torqued..IF all that is normal then its a leak from either warped manifold flanges, warped carb bases or sticking out board butterflies do to the carbs being warped.

Go to youtube and watch Harold Demes six pack videos. You will learn a lot. If you need them worked on send them to him or Allstate but under no circumstance send them to the HOlley Speed shop. They are butchers and hacks
https://www.youtube.com/results?sear...wer+carburetor

 

Another possibility is that you have the center carb idle adjust set too high openning the butterflies open too far and are idling on the transition slot instead of the idle circuit. Did you see any change when you adjusted the idle set screws? The correct setting is the idle set so that the butterflies have a pin point openning on the transition slot and you adjust the idle with the idle mixture screws. IF you cant there are other things you can do to insure that that transition slot is mostly covered

 

Rescue, for clarification, I said to completely remove the rods as in no longer on the engine. That is why I did not say "disconnect the rods", for the reason you mentioned.

 

JUst letting the OP know...Reading your post quickly or not knowing exactly what you meant would be a bad day for him. Thats why I had said that after my initial statement. Someone being new or not knowledgeable about how these things function can jump to a conclusion and not know what will happen further on down the line. You have years of experience with these things and now do things out of instinct and knowledge versus a new guy that has to be told all the small things. Which is another thing that I missed......

For the O.P. Adjusting the idle set screw with the outboard carbs connnected can cause the outboard butterflies to crack open causing a "vacuum leak" as they will lei it more air than you want at idle. YOu need to get the car to operating temps so that any heat expansion has occurred and the choke is fully shut, shut off the motor and then disconnect the outboard linkage. Make sure it wont hang up on the manifold. Restart the motor and verify your timing is where you want it. Reset your idle and idle mixture screws. Shut down the motor and test openning the outboard butterflies and ensure they fully close on the vaccum pod spring themselves. THe pods internal spring should let them rotate closed by themselves without hanging up. Then screw the outboard linkage arms a bit then slip them in so that they fit into the holes without pulling on the throttle levers. restart and see if anything has changed.

 

Yes I saw changes when adjusting the curb idle screw and with it's rpm adjusting. Then when I also did the air/fuel ratio screws on each side, the car was responding to both of those screw changes. This leads me to believe that it is the high idle cam sticking on the linkage. My question would really be does anyone have a video showing how the hot idle cam works on these carburetors because I all could find were videos with adjusting newer electric choke carburetors. Thanks for all the responses

 

Im looking. There are how to's foe Quadrajet divorced chokes...still looking for holley. Make sure the choke pull off is working, it has a vacuum line going to it. If you can manually push the choke rod up you can see how it works. The high speed idle is green and there is an arm with a square end. There is a slot the fits a flat head screwdriver. It is adjusted By twisting the square end so it catches more or less steps on the green ramps when you step on the thrttle to set the choke on a cold engine.

If you get your motor hot then pull the valve cover that green ramp should move freely and the sqare on the Lever should bot be touching it

 

Here I’m going to attach a few photos of my car’s choke linkage. Let me know if you guys think anything looks out of the ordinary. The pictures are also taken with the choke fully open




I also would be tempted to fully disconnect that fast idle cam because I have no use for it as I live in San Diego and the coldest it ever gets is high 40s or low 50s

 

You can see where the square is touching withe red arrows. Just use a screw driver in the slot and twist it so it doesnt touch when its warmed up

 

Just twisted that linkage and it doesn't rub it now when warmed up. It made the issue better from reducing it from getting stuck at 2000 rpms to now around 1500ish. The weird thing is that when It would hang around 1500 I would turn down my curb idle speed to where it would be at a good idle. Then when I would rev it up the rpms would fall without hanging. So my main question is do you think that I just had my idle speed screw to far high so when it was colder it would idle but when up to temperature it would stay in too high of rpms?

Also I have been doing my homework and watching a lot of Harold demes YouTube videos, I was wondering if you have his contact information so that I could talk to him as well. Thanks

 

The choke will effect a cold motor regardless of air temp as the springs are set to 180 plus degrees. You can pull the clip and pull that plastic piece out or leave it and set the choke so it stays at 1500 rpm when the engine is started and will go down after its hot. Im sure it wont take long to waarm up in your neck of the woods.

Theres another thread that may have his email. I will look if someone else doesnt post it before i can

 

Heres another thread thats a Good read
https://www.corvetteforum.com/forums/c3-tech-performance/4654077-tri-power-carb-and-intake-issues-rebuild-fix-thread.html

 

Harolds email as it was given to me. I havent talked with him yet
mailto:chucknorbid@gmail.com

 

team
anyone have a clue where to find that plastic high idle plastic cam sproket. I have the opposite problem the center carb choke works fine but the motor falls on its face because it cant hold the fast idle
thanks Bob

 

its on the passenger side right next to the linkage for the air/choke flap.

 

open this link and there is a pic in thew first post... the big green plastic thing is the choke cam, the metal square piece sets the choke, where the throttle is held is controlled by the metal square with the flat screw driver blade slot. YOu stick a screw driver in that and twist the square to touch the cam steps at the correct speed for where the choke is set for a given temp

https://www.corvetteforum.com/forums...wer-choke.html