Idle Issue - '72 LT1
Thread Starter
Intermediate
Joined: Apr 2013
Posts: 37
Likes: 0
Idle Issue - '72 LT1
I could use some advice regarding an idle issue on my 1972 Corvette LT1. The engine is completely rebuild, has a solid lifter camshaft, 9.5:1 compression, and the original (fully restored) holley carb; it made 408 HP at 6000 RPM on the dyno. I have about 9,000 miles since completing a frame-off restoration.
The issue is that I can't get the engine to idle smoothly below 1,200 RPM; otherwise the engine runs great and performs extremely well. If I adjust the idle speed via the solenoid, the engine will run at 900 RPM but will slowly die. The idle mixture screws are currently backed out 2-1/2 turns. How many turns is typical? I have read anything from 1-1/2 to 4 turns.
I would appreciate your thoughts.
Thanks.
The issue is that I can't get the engine to idle smoothly below 1,200 RPM; otherwise the engine runs great and performs extremely well. If I adjust the idle speed via the solenoid, the engine will run at 900 RPM but will slowly die. The idle mixture screws are currently backed out 2-1/2 turns. How many turns is typical? I have read anything from 1-1/2 to 4 turns.
I would appreciate your thoughts.
Thanks.
Le Mans Master
Joined: Oct 2010
Posts: 6,903
Likes: 834
From: melbourne florida
2023 C3 of the Year Finalist - Modified
Hook up a vacuum gauge and adjust it to your highest vacuum reading,then re adjust your idle .don't play with the solonoid that's not how you adjust the carburator. Send Lars an e mail and get his carb adjusting papers.
Last edited by 7t9l82; Apr 26, 2016 at 09:50 PM.
Le Mans Master
Joined: Oct 2010
Posts: 6,903
Likes: 834
From: melbourne florida
2023 C3 of the Year Finalist - Modified
Really you are better off getting Lars to send you his holley papers by email, there is alot of detail and it takes you step by step through it. He doesn't charge anything for them.there is a positivity you have a vacuum leak too. CHeck for that first.
Instructor
Joined: Apr 2016
Posts: 104
Likes: 7
From: Denver Colorado
I could use some advice regarding an idle issue on my 1972 Corvette LT1. The engine is completely rebuild, has a solid lifter camshaft, 9.5:1 compression, and the original (fully restored) holley carb; it made 408 HP at 6000 RPM on the dyno. I have about 9,000 miles since completing a frame-off restoration.
The issue is that I can't get the engine to idle smoothly below 1,200 RPM; otherwise the engine runs great and performs extremely well. If I adjust the idle speed via the solenoid, the engine will run at 900 RPM but will slowly die. The idle mixture screws are currently backed out 2-1/2 turns. How many turns is typical? I have read anything from 1-1/2 to 4 turns.
I would appreciate your thoughts.
Thanks.
The issue is that I can't get the engine to idle smoothly below 1,200 RPM; otherwise the engine runs great and performs extremely well. If I adjust the idle speed via the solenoid, the engine will run at 900 RPM but will slowly die. The idle mixture screws are currently backed out 2-1/2 turns. How many turns is typical? I have read anything from 1-1/2 to 4 turns.
I would appreciate your thoughts.
Thanks.
Did you rebuild the Holley? If so did you remember to put new mixture screw seals in the holes where they screw in? If you failed to put new seals in those holes it will suck air along with the fuel. The typical adjustment of those screws is 1-1/4 to 1-1/2 turns out but with leaking seals they'll require 2 to 3 times that much. Does the car have A/C? If so I would suspect the solenoid is used as a fast idle aid when the A/C is ON and the actual method of adjusting the idle speed would be the screw in the base plate.
Race Director
Joined: May 2006
Posts: 18,626
Likes: 2,553
if you look at the emissions sticker for a 72 LT-1 the solenoid is used to adjust the idle speed not a screw on the base plate. The instructions call for the adjustments to be made with the gas cap removed, the vacuum hose to the distributor removed and plugged. If the engine ran on the dyno without a problem did you forget to connect any vacuum lines when you installed the engine. Why do you have to readjust anything if it ran on the dyno? What transpired between the dyno run and now?
Thread Starter
Intermediate
Joined: Apr 2013
Posts: 37
Likes: 0
The engine ran well on the dyno but once installed in the car, the idle quality was poor. The '72 Corvette has several vacuum connections which the dyno does not simulate. Who is Lars? How do I contact him to get the information?
Thanks.
Thanks.
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Melting Slicks
Joined: Oct 2010
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From: "ɹǝpunuʍop", Adelaide, South Australia
Race Director
Joined: May 2006
Posts: 18,626
Likes: 2,553
Vacuum connections
Can you disconnect and plug those connections and see if you can then correctly adjust the carburetor?
Le Mans Master
Joined: Dec 2003
Posts: 5,727
Likes: 38
From: Fremont CA
Sounds like you might have an issue in your cars chassis vacuum system. Isolate the motor by itself and tune it.....then add the brake booster into the system.....then chassis vacuum system.....then isolate wipers from headlamps.......work your way around.....
