Holley choke adjustment

[Gary S.]

Good morning to all. I am having a bit of trouble with the Holley on my 1972 LT-1, which I just took out of hibernation. This is the original carb, rebuilt by Jerry MacNeish two years ago. The carb is flawless in appearance and when warm. Here's the rub - if I pull the air cleaner and manually pull the accelerator rod, the carb goes on to the high idle cam and stays there. As soon as I start the car, the carb falls off of the high idle cam and stays off no matter how much "blipping" of the throttle I do. I don't really understand the workings of the carb and why it falls off of high idle as soon as I start the engine. It almost appears as if the vacuum is pulling the carb off of the high idle cam, but then I am clueless on this part of the carb.

Any thoughts? I am comfortable with the basics of the carb, idle and float adjustment, and I had previously taken it apart to install new gaskets. Beyond that, I am somewhat in the dark on the idle system and secondary system.

Thanks in advance,
Gary

[Clem Z.]

Re: Holley choke adjustment

Good morning to all. I am having a bit of trouble with the Holley on my 1972 LT-1, which I just took out of hibernation. This is the original carb, rebuilt by Jerry MacNeish two years ago. The carb is flawless in appearance and when warm. Here's the rub - if I pull the air cleaner and manually pull the accelerator rod, the carb goes on to the high idle cam and stays there. As soon as I start the car, the carb falls off of the high idle cam and stays off no matter how much "blipping" of the throttle I do. I don't really understand the workings of the carb and why it falls off of high idle as soon as I start the engine. It almost appears as if the vacuum is pulling the carb off of the high idle cam, but then I am clueless on this part of the carb.

Any thoughts? I am comfortable with the basics of the carb, idle and float adjustment, and I had previously taken it apart to install new gaskets. Beyond that, I am somewhat in the dark on the idle system and secondary system.

Thanks in advance,
Gary

sound like the choke pull off,vacuum break, is not set correctly and is pulling the choke open to far on startup. the pull off should just open the choke part way till the temp come up and opens the choke all the way.

[Joe C.]

Re: Holley choke adjustment

Good morning to all. I am having a bit of trouble with the Holley on my 1972 LT-1, which I just took out of hibernation. This is the original carb, rebuilt by Jerry MacNeish two years ago. The carb is flawless in appearance and when warm. Here's the rub - if I pull the air cleaner and manually pull the accelerator rod, the carb goes on to the high idle cam and stays there. As soon as I start the car, the carb falls off of the high idle cam and stays off no matter how much "blipping" of the throttle I do. I don't really understand the workings of the carb and why it falls off of high idle as soon as I start the engine. It almost appears as if the vacuum is pulling the carb off of the high idle cam, but then I am clueless on this part of the carb.

Any thoughts? I am comfortable with the basics of the carb, idle and float adjustment, and I had previously taken it apart to install new gaskets. Beyond that, I am somewhat in the dark on the idle system and secondary system.

Thanks in advance,
Gary

Gary,

You are correct, in that the choke pulloff diaphragm/link will do just that. In warm weather, this is normal, as smog carbs are designed to come off choke quickly. There are 2 fixes:

1. Set choke, turn key with throttle closed, and leave it there. Do not open throttle until you're ready to release the choke.

2. Set choke spring 1-2 index marks "richer".

These suggestions are made, assuming that the fast idle speed link is set to the proper length, and that the fast idle speed screw is set properly. If either of these are not set correctly, then you should look at the Shop Manual for adjustment procedure. You can also call Holley Tech Support for procedure. Yours is a model 4160. If you post the list number, we can give you a link to Holley "Carb Numerical Listing" chart with relevant specs.

http://www.holley.com/data/TechService/Technical/4150-4160%20Exploded%20View.pdf

Joe

[Terry M.]

Re: Holley choke adjustment

The Holley on the 1970-1972 small blocks is the "divorced choke" style with a coil spring in a well in the intake manifold. There is no way to set the spring to any index marks.

I don't have access to the adjustment procedure or the list numbers at the moment, but the procedure involves bending the rod connecting the coil spring to the choke plate arm using a rod or drill bit of the proper diameter to set the opening of the choke while holding the vacuum pull-off with a rubber band holding the throttle linkage open. Three hands would be useful for this. It is an adjustment that must be done on the car, and can not be correctly done otherwise.

All the dimensions, and a step-by-step procedure, with illustrations, are in the Chassis Service Manual (CSM). This should be on your list of essential tools to "take care of your baby," as some on this board are wont to say.

[Gary S.]

Re: Holley choke adjustment

The Holley on the 1970-1972 small blocks is the "divorced choke" style with a coil spring in a well in the intake manifold. There is no way to set the spring to any index marks.

I don't have access to the adjustment procedure or the list numbers at the moment, but the procedure involves bending the rod connecting the coil spring to the choke plate arm using a rod or drill bit of the proper diameter to set the opening of the choke while holding the vacuum pull-off with a rubber band holding the throttle linkage open. Three hands would be useful for this. It is an adjustment that must be done on the car, and can not be correctly done otherwise.

All the dimensions, and a step-by-step procedure, with illustrations, are in the Chassis Service Manual (CSM). This should be on your list of essential tools to "take care of your baby," as some on this board are wont to say.

Actually, I do have the 1972 GM Service Manual. Unfortunately, I didn't/don't really understand how the divorced choke system and vacuum pulloff works so reading that was like reading some electrical engineering book.

Ok, I will break the manual out, figure out what the parts are and what they are called and then do an on-the-car adjustment. Your comment, Terry, about bending the rod connecting the coil spring... seems to make sense. Between the comments, the parts breakdown and the SM, I should be able to get this fixed.

Stay tuned - news at 11.

Thanks Terry and all.

Gary

[Charlie C.]

Re: Holley choke adjustment

One other thing not related to choke that Terry mentioned to me years ago is to make sure that you have the insulating gasket which is about 1/4" thick between the carb and the manifold. Adding this made a significant differenct in how the carb performed. It keeps the gas from getting too hot in the carb.

1972 LT-1