Wont idle down. Vac leak, timing, carb or ????
07-03-2016, 03:43 PM
#1
1st Gear
Thread Starter
Member Since: Apr 2015
Location: Happy Vette City Vetteville
Posts: 1
Likes: 0
Received 0 Likes
on
0 Posts
Wont idle down. Vac leak, timing, carb or ????
Hi all,
Long term lurker but first post.
I have a project 81 car. its a 4 speed with a GM crate 350. Has sidemount exhaust, smog delete. New HEI distributor and rebuilt quadrajet. New Harmonic balancer, TDC verified.
Now, I'm getting older and seem to have forgotten more than I can remember so take it easy on an old guy.
Finally got the car running and was excited that she started on its first attempt. When cold, high idle was around 14-1500rpm. After a few adjustments and after it was warmed up fully, could not get the idle down below 1000rpm.
I'm thinking of either a vacuum leak, timing off or a poorly adjusted carb.
Here is what I plan to do.
Block off all ports on the carb and see if it makes a difference. If it does I know its a vacuum issue somewhere.
Timing, have it set to 34 degrees all in by 2800rpm vac disconnected and plugged. Vacuum advance limited to 14 degrees.
Carb, tried to set up as per all the various things I have found online. Winding the idle mixture screws in all the way kills the engine.
Have it set for best vacuum at idle.
I did notice the choke flap when engine hot was still quite loose and could easily be moved by air flow and engine vibration. Should the flap not be held fairly securely by the choke spring?
I did wonder if perhaps it wasn't coming off the fast idle cam but only thought about this after I came in from the garage.
At the moment, the idle speed screw is backed all the way out and is not even touching the throttle shaft, as far as I could see the throttle butterflies were closed.
What do I need to re check/verify and what else could be causing my issues.
Unfortunately I'm not very good with technology and do not possess a digital camera.
Thank you.
John.
Long term lurker but first post.
I have a project 81 car. its a 4 speed with a GM crate 350. Has sidemount exhaust, smog delete. New HEI distributor and rebuilt quadrajet. New Harmonic balancer, TDC verified.
Now, I'm getting older and seem to have forgotten more than I can remember so take it easy on an old guy.
Finally got the car running and was excited that she started on its first attempt. When cold, high idle was around 14-1500rpm. After a few adjustments and after it was warmed up fully, could not get the idle down below 1000rpm.
I'm thinking of either a vacuum leak, timing off or a poorly adjusted carb.
Here is what I plan to do.
Block off all ports on the carb and see if it makes a difference. If it does I know its a vacuum issue somewhere.
Timing, have it set to 34 degrees all in by 2800rpm vac disconnected and plugged. Vacuum advance limited to 14 degrees.
Carb, tried to set up as per all the various things I have found online. Winding the idle mixture screws in all the way kills the engine.
Have it set for best vacuum at idle.
I did notice the choke flap when engine hot was still quite loose and could easily be moved by air flow and engine vibration. Should the flap not be held fairly securely by the choke spring?
I did wonder if perhaps it wasn't coming off the fast idle cam but only thought about this after I came in from the garage.
At the moment, the idle speed screw is backed all the way out and is not even touching the throttle shaft, as far as I could see the throttle butterflies were closed.
What do I need to re check/verify and what else could be causing my issues.
Unfortunately I'm not very good with technology and do not possess a digital camera.
Thank you.
John.
07-03-2016, 04:16 PM
#2
Melting Slicks
See if anything is binding or holding the throttle blades open.
Especially the throttle cable. Do you have the recommended two springs pulling it closed?
Especially the throttle cable. Do you have the recommended two springs pulling it closed?
Last edited by mikem350; 07-03-2016 at 04:19 PM.
07-03-2016, 04:55 PM
#3
Zen Vet Master Level VII
My .02 on getting your idle down....
I'm thinking of either a vacuum leak, timing off or a poorly adjusted carb.
Here is what I plan to do.
Block off all ports on the carb and see if it makes a difference. If it does I know its a vacuum issue somewhere.
Timing, have it set to 34 degrees all in by 2800rpm vac disconnected and plugged. Vacuum advance limited to 14 degrees.
Yes, vacuum leaks are the pain of our existence- I bet you find some issues as we all do. I'd start there.
14 seems pretty high. You can knock down the idle speed quite a bit if you bring her back to 8. I'd adjust that one after the vacuum leaks.
I'd mess with the carb last.
Good luck and keep us looped in on your progress.
I'm thinking of either a vacuum leak, timing off or a poorly adjusted carb.
Here is what I plan to do.
Block off all ports on the carb and see if it makes a difference. If it does I know its a vacuum issue somewhere.
Timing, have it set to 34 degrees all in by 2800rpm vac disconnected and plugged. Vacuum advance limited to 14 degrees.
14 seems pretty high. You can knock down the idle speed quite a bit if you bring her back to 8. I'd adjust that one after the vacuum leaks.
I'd mess with the carb last.
Good luck and keep us looped in on your progress.
07-04-2016, 06:25 PM
#4
Team Owner
A Q-Jet has a 'fast idle' adjustment (for start-up idle when on choke) and a curb idle adjustment. You need to make sure they are both set properly.
Last edited by 7T1vette; 07-04-2016 at 06:26 PM.