A Little Help From Holley Users

Boo Boo Foo said:

My current carburettor is a 600CFM Vac Secondary 80457-2 model. Can I confirm the following please? (I haven't taken it off yet) Would my particular carby ALSO have the "little hidden stop screw in the base plate" as per the carby originally mentioned in this thread? If so, does anyone have a link to a source of photos or an online manual regarding my model? Since I first read this thread, I've done probably a hundred man hours of online research - including the official Holley site. But the secondary idle circuit reference seems to be thin on the ground.

Thanking everybody in advance for the wonderful learning curve in this thread.

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There is no secondary idle circuit on a Holley 80457. This is a 4160 model Holley, which have a secondary metering PLATE, in place of the model 4150's secondary metering BLOCK. ( this is the main difference between the two models, most other parts of these are interchangeable). As for your hiden stop screw, it's either there or not, it's not hidden, if it's there, it's on the passenger side of the carb, where the throttle rod pokes out. I've never had to mess with this screw,( all my engines idled without needing to have extra air flow) and never really paid much attention to what carbs had it and which ones didn't. The only Holleys that have a secondary idle circuit, are the 4150's ( some not all) and these are obvious, as they have the mixture screws sticking out the sides of the metering blocks ( not plates)

Have you checked vacuum since you have been tuning? Just curious if it has gone up.

D.Hearne said:

There is no secondary idle circuit on a Holley 80457. This is a 4160 model Holley, which have a secondary metering PLATE, in place of the model 4150's secondary metering BLOCK. ( this is the main difference between the two models, most other parts of these are interchangeable). As for your hiden stop screw, it's either there or not, it's not hidden, if it's there, it's on the passenger side of the carb, where the throttle rod pokes out. I've never had to mess with this screw,( all my engines idled without needing to have extra air flow) and never really paid much attention to what carbs had it and which ones didn't. The only Holleys that have a secondary idle circuit, are the 4150's ( some not all) and these are obvious, as they have the mixture screws sticking out the sides of the metering blocks ( not plates)

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I'm reasonably sure they all have it. It may not be totally hidden, but it isn't glaringly obvious, and can't be adjusted in most cases without removing the carburetor so I refer to it as hidden for lack of a better term as "isn't glaringly obvious, and can't be adjusted in most cases without removing the carburetor" is a bit cumbersome , you can call it whatever you like. Opening the secondary air gap simply provides additional air for idle speed, so that the primary can be closed down a bit. This is useful when setting the idle with only the primary causes the transfer slots to be uncovered. This serves the same purpose as holes drilled in the throttle plate(s) (which is the next step). Some Holley’s are notorious for needing this with radical cams (3310's for example) Some Holley’s have holes in the throttle plates from the factory thus work without this on radical cams. Demon now has the "idle eze" feature to overcome this problem.

However, DHearne is correct about it not being an "idle circuit" 4160 and a good portion of 4150s do not have 4 corner idle. My own 3310 is now a 4150 (Holley sells a kit to do this) but still doesn't have 4 corner idle.

If you cannot locate a picture online, shoot me an E-Mail and when I get home (a few weeks) I'll take a photo of it for you.

PoliceInterceptor said:

I'll take a photo of it for you.

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I can snap a pic if you need. What part is a pic needed?

brianj5600 said:

I can snap a pic if you need. What part is a pic needed?

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Boo Boo Foo was asking for a picture of the mostly hidden secondary stop screw...