Holley 4160 vs dp fast idle ??

Hack · May 15, 2007

I have a Holley 4160 vacuum secondary double pumper on my 302 in my '70. It's an 89 roller motor with a Weiand Stealth and Duraspark ignition. This project is always second fiddle to other things I've got going, so it's been taking me a LONG time to finish.

Anyway, the carb wants to idle at 2,000-2,500 rpm. I have a Holley carb manual, and I've removed it and done the adjustments in the book. Should I be looking for a vacuum leak? I replaced all the vacuum hoses when I did the swap, so I don't have old, cracked stuff in there.

Any other thoughts of what I should start with? I'm also wondering if there isn't something wrong with the linkage. I've noticed that the curb idle screw doesn't even touch the linkage. There's a little slack in the throttle cable, so it isn't being held open.

Could a poorly adjusted choke do this?

BlackGMC · May 15, 2007

It kinda sounds like a big vacuum leak or the choke is stuck. How long do you let it idle? Did you try and rev it a few minutes after startup to see if it will release the choke? I think there is linkage on the choke side connecting it the butterflys. Check to see if the linkage is touching.

rbohm · May 15, 2007

first, i have never heard of a vacuum secondary carb with a second accelerator pump(aka double pumper). if someone converted a vacuum secondary card to a double pumper, it is likely poorly done, and the secondaries are being held open slightly.

ratio411 · May 15, 2007

NEVER convert a vacuum secondary to mechanical secondary (ala double pump)

Without the second accelerator pump circuit, you are crippling the carb and it will cause all sorts of maladys.
I agree with rbohm, if this mod has been made, your linkage is compromised and could be stuck open in a high idle position.

Has the intake been off recently?
A mis-seated intake gasket can leak too.
I have seen vacuum leaks occur inside the lifter valley due to a bad seating of the intake gasket on the bottom of the ports.

Dave

Hack · May 17, 2007

I must have gotten the name wrong. It's new, not modified and it is a 4160 with vacuum secondaries. My Holley carb manual describes a 4150 and 4160 in the same section and the wording is a little confusing to me.

I got a few minutes to work on the car yesterday and I pulled off the vacuum lines to the tranny and dizzy and plugged them. That maybe got me 100 rpm less, but not the solution.

I have access to an identical carb on a friend's '83 Capri, so I'm going to try a carb swap next to eliminate the carb as the cause.

D.Hearne · May 17, 2007

Holley terms to remember: "Double pumper" is not to be confused with "Dual line or Feed" A 4160 is a vacuum secondary without a secondary metering block. 4150 can be either a vacuum sec. or a double pumper (mechanical sec.) And if I'm not mistaken, the 660 center squirter carbs are also 4160's that lack the metering block on the secondary side but are mech. secondary carbs.

ratio411 · May 17, 2007

You're dead on D...
The difference between 4150 and 4160 is if they have a secondary block, or just a plate under the bowl.

This is super easy to convert though.
A spare block and 4 longer bowl screws and you have rear jets.
That's the way I prefer it anyway...

Hack · May 20, 2007

Well, I ended up pulling and reinstalling the intake, which made absolutely no difference.

I swapped my friend's 600 Holley onto it to see if that would change things and now it runs perfectly. So now I know it's my carb, but I have no idea what's wrong. I've been through the adjustments in the manual and they didn't even change the idle.

Could something be cracked causing a vacuum leak inside the carb?

D.Hearne · May 20, 2007

Completely remove the choke assembly and try it again. Wire the choke plate open. It's also possible there's a passage plugged in the metering block. I use spray carb cleaner in all passages, then blow them out with compressed air to be sure that doesn't happen

67efivert · May 20, 2007

does the carb have a manual choke or an elerctic the is a fast idle cam under the choke assembly that may be adjusted wrong eithor way look there

Hack · May 21, 2007

There are two adjustments you do with the carb off the engine. One screw sets how far the main throttle plates are open when the throttle is closed. The manual I have says to use a 0.035" drill. The second adjustment sets the secondary plates. It says to turn the screw in until you see the plates move and then one full turn more.

Well, when I follow those directions the carb idles at 2,000 rpm.

I looked at my buddies' 600 Holley that worked and just put my screws where his were. Essentially it just closed both sets of throttle blades 2 or so turns on their screws. Then I put the carb on the car and turned down the idle screw. It works great now.

Thanks for all the suggestions. I was lucky to have a second carb around; otherwise I probably would have ended up paying someone to do this. Who would have thought it would be something so simple.

D.Hearne · May 21, 2007

Both those adjustments sound far fetched to me. On the primary side throttle screw (idle speed scew) I completely close it then turn it till the screw just starts to move the throttle linkage. After that, I adjust it as needed after playing with the mixture screws and timing. I never have adjusted the secondary shaft blades, they're just not needed to let the engine idle. I have a few times found that a too light secondary spring and an engine that draws a lot of vaccum (the roller 302 in my Ranger is one, and using that same carb Holley 600 on a 390) will pull the secondaries open at idle and play hell with trying to set the primary idle.

Hack · May 22, 2007

D.Hearne said:
Both those adjustments sound far fetched to me. On the primary side throttle screw (idle speed scew) I completely close it then turn it till the screw just starts to move the throttle linkage. After that, I adjust it as needed after playing with the mixture screws and timing. I never have adjusted the secondary shaft blades, they're just not needed to let the engine idle. I have a few times found that a too light secondary spring and an engine that draws a lot of vaccum (the roller 302 in my Ranger is one, and using that same carb Holley 600 on a 390) will pull the secondaries open at idle and play hell with trying to set the primary idle.

Thank you for the tips. After the little bit of time I've spent playing with my carb, I believe that your advice is much better than what I saw written in the Holley carb manual. That manual had both sets of the throttle blades WAY too far open.

D.Hearne · May 24, 2007

Holley 4160 vs dp fast idle ??

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