66 Coupe - 427/425 Holley 4150 Fast Idle adjust

[John L.]

66 Coupe - I am trying to do a final fast idle adjust on my Holley 3247 (4150). I have read John Z's article and the Chev Chassis Overhaul Manual on how to do this however I still have a question. I know I have to bend the tab that controls the step on the plastic cam. The question is -- when and how do you bend it. I know you use a flat bladed screwdriver. Do you bend it with the plastic cam all the way down and out of the way ??? Do you bend it with the plastic cam half way up ?? How firm should the tab be against the plastic cam ?? Hot Engine or Cold Engine ?? thanks in advance

[Marco H.]

Re: 66 Courpe - 427/425 Holley 4150 Fast Idle adjust

There are two parts to the operation of the choke. The spring on the intake, and the cam pushing against the tab. Assuming the spring works as intended (not worn out or tired), it will, based on ambient temperature, push the cam up more or less, upon depressing the gas pedal. (Setting the choke). The tab will allow a final RPM adjustment. To accomplish that, you need to set the choke on a cold engine and fire it up. While running, you can adjust the tab, as you mentioned, with a flat blade screw driver. I believe the 66 427/425 is expected to go to 1700+- RPM upon start up and the rise as it warms up. The PV manual will have the specific and correct data listed.
The "hot choke" RPM (as it is mentioned in the Chevy Service Manual), is considered the RPM with the choke engaged and the engine warmed up (before you kick the choke out.)

Hope this helps,
Marco

[John L.]

Re: 66 Courpe - 427/425 Holley 4150 Fast Idle adjust

Marco - thank you very much for this response. An NCRS friend from the Delaware Valley Chapter I once belonged to, before the health issues, also saw this post and called me and had her husband go over the procedure with me. I was able to also ask additional questions during the call. He also saw your post and said you were spot on with your response. Kudos and thanks to both of you as I now have a good starting point and will do some more tuning tomorrow morning.

[Duke W.]

Re: 66 Courpe - 427/425 Holley 4150 Fast Idle adjust

To accomplish that, you need to set the choke on a cold engine and fire it up. While running, you can adjust the tab, as you mentioned, with a flat blade screw driver. I believe the 66 427/425 is expected to go to 1700+- RPM upon start up and the rise as it warms up. The PV manual will have the specific and correct data listed.
The "hot choke" RPM (as it is mentioned in the Chevy Service Manual), is considered the RPM with the choke engaged and the engine warmed up (before you kick the choke out.)

Hope this helps,
Marco

Just to be clear the fast idle speed specified in the service manual is set with the engine fully warmed up, and on a cold start the initial fast idle speed, once stabilized, will typically be 200-300 revs less.

Duke