1957 Holley 4160 tuning

[Boozeman]

Good morning, all -

I've swapped out my Holley 4150 for a new 4160 due to my carb bowls and accelerator pump cover on the 4150 being warped and leaking over these many years. I have not played with the jets on the 4160 yet - this is just as the carb came out of the box. In tuning the carb and the timing with my vacuum guage, I'm pulling an maximum of 20 inches of vacuum, which is good. My idle is sitting right at about 500 rpm. However, I have the idle screw completely backed out to get there. Is this normal? Seems like I should have to screw in the idle screw some to get the correct idle (I did on my 4150). Any and all ideas appreciated!

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[Jay Fitzpatrick]

Good morning, all -

I've swapped out my Holley 4150 for a new 4160 due to my carb bowls and accelerator pump cover on the 4150 being warped and leaking over these many years. I have not played with the jets on the 4160 yet - this is just as the carb came out of the box. In tuning the carb and the timing with my vacuum guage, I'm pulling an maximum of 20 inches of vacuum, which is good. My idle is sitting right at about 500 rpm. However, I have the idle screw completely backed out to get there. Is this normal? Seems like I should have to screw in the idle screw some to get the correct idle (I did on my 4150). Any and all ideas appreciated!

I just replaced my 57 stock carb with a Holly 9510 w/ an electric choke. The new carb was revving way too high even with the idle screw not engaged. There is, however, another idol screw hidden under the choke, and when I let that out all the way, the reves came way down and I could then adjust the primary idol screw to get the proper rpm's. Worked for me.

 

[Boozeman]

I just replaced my 57 stock carb with a Holly 9510 w/ an electric choke. The new carb was revving way too high even with the idle screw not engaged. There is, however, another idol screw hidden under the choke, and when I let that out all the way, the reves came way down and I could then adjust the primary idol screw to get the proper rpm's. Worked for me.

Thank you for that information, Jay - very helpful! I've seen there is a mod by which you can remove that screw and replace with a allen head screw or a thumbscrew to make adjusting it easier. I'll try adjusting that screw to see if it will help my condition, and report back.

 

[Ward 57]

I had my carb rebuilt after the power valve started leaking probably due to the ethanol in the gas. It too would not come down to a low idle. I could force it down by manually pushing down the linkage. I was expecting the springs on the carb itself to pull the idle down. Nope, I then readjusted the throttle linkage lengthening it and used the throttle return springs on the linkage itself to bring the idle down. MUCH stronger springs and now it works perfectly.

 

[Boozeman]

I had my carb rebuilt after the power valve started leaking probably due to the ethanol in the gas. It too would not come down to a low idle. I could force it down by manually pushing down the linkage. I was expecting the springs on the carb itself to pull the idle down. Nope, I then readjusted the throttle linkage lengthening it and used the throttle return springs on the linkage itself to bring the idle down. MUCH stronger springs and now it works perfectly.

Thank you to Jay and Ward for the advice. Removed the secondary idle screw and replaced it with an allen head screw last night. Got the carb back on the car, and adjusted the linkage out a bit. With the secondary idle backed off and the linkage adjusted further out, I got a pretty solid idle. I still didn't have to use much on the primary idle screw to get there, but it now idles at right about 600 rpm. Thanks again!

 

[Ward 57]

Thank you to Jay and Ward for the advice. Removed the secondary idle screw and replaced it with an allen head screw last night. Got the carb back on the car, and adjusted the linkage out a bit. With the secondary idle backed off and the linkage adjusted further out, I got a pretty solid idle. I still didn't have to use much on the primary idle screw to get there, but it now idles at right about 600 rpm. Thanks again!

Just remember that the secondary idle is for the cold start idle setting. Check your choke setting as this is what activates the secondary idle. Hills has just the thermostat spring by itself if yours is worn out. Many others sell the spring & cap together. Mine didn't work for years until I figured out the logic.