Holley 4150 Fast idle adjustment

[Dick G.]

My fast idle on my 65 350HP corvette is not functioning. It is a Holley 4150. I went out this morning and with the choke closed, still no fast idle. I have most of the shop manuals for this car but still not sure which is my fast idle cam or how to proceed to adjust. Should I remove carb from car?Can someone give more details?
Thanks
DG

[Jimmy G.]

Re: Holley 4150 Fast idle adjustment

I just rebuilt one this am for a 396. Fast idle screw is hidden below the choke body. It is a real pain to adjust but it can be done with a 1/4 " wrench I think. Helps if you are a double jointed person with fingers the size of a small girl also. Make sure all the cams, rods, and linkages are free and moving as well as the choke plate in the main body. Some times these parts can jam and cause issues. Also make sure the thermostatic coil is working as it is engineered.

[Dick G.]

Re: Holley 4150 Fast idle adjustment

Jimmy
When do you adjust this screw? Should I do this when the engine is cold? I will need to hook up my tach and adjust to 1750rpm, but again what temp should the engine be at? I would guess the optimum time to adjust fast idle is with a cold engine with choke closed, correct?
Thanks
DG

[Jimmy G.]

Re: Holley 4150 Fast idle adjustment

Engine has to be cold, normally . However you can cheat the system by manually closing the choke therefore setting the fast idle and watching the difference in the accelerator rod position on fast idle versus normal. In fact, with the car running at idle, you can set the idle on the hi rpm notch on the fast idle cam and adjust it then. It is a little more difficult this way, but possible. Generally if you set the choke after the car is warm, it dies from being too rich, but the choke and fast idle cam are independent of each other. A quick flick of the accelerator will reset it to normal idle position.

[Clem Z.]

Re: Holley 4150 Fast idle adjustment

the fast idle speed in the GM shop manuals is with a fully warmed up engine. you set the pri throttle opening with a specific diameter wire gage using the fast idle screw with the choke closed with the carb off of the engine. then adjust it on the engine after warm up