I'll try to post a couple pics. 1) Is a screw of the proper thread with spring & lock nut on a Holley 570CFM "Street Avenger" hot rod series carb. It's on a moderately built 302 with a lopey cam and in this case, the ability to adjust the secondaries on the fly is nice.   2) Quick Fuel uses an Allen set screw.  Just my $.02   hope this helps, JEFF.............


64F100 57FAIRLANE500

With the carburetor on the engine, I’ve simply bent the secondary idle tab appropriately to get more or less air at that point to get the primary throttle blades in a more conducive transfer slot positioning.  This has eliminated the need to pull the carb off the engine and do a bottom side screw adjustment.  A pair of needle nose pliers has been used for that minor tweaking.

Lorena, Texas (South of Waco)

Got it! Thanks Steve.

  

Mark - This the stamped tab I am speaking of - and of course I could only find a picture of a carb that has the screw...... It would be nice if you could get the blocking screw out of the way and drill / tap for the proper item - but......


 
 Steve Metzger       Tucson, Arizona

Good suggestion. I will try that Tomorrow. I have another 390 which needs a rebuild and it has the adjusting screw in the Base and it does adjust the opening. Don't know why Holley changed the ability to use that Screw. I could probably swap the Bases but I don't have any Gaskets handy.  I will try your Way.

  

Mark, take a look at the point where the missing screw "should be" touching the vacuum secondary shaft linkage. That's where I have had to twist the sheet metal a bit to accommodate the need to open the secondary butterflies a bit. Its the stopping point for the vacuum pot - that keeps the rear butterflies from jamming when tightly closed. Seems like - this has been a year or three - I stuck a feeler gauge in there for a trial. 

 
 Steve Metzger       Tucson, Arizona

I it back together Today. It runs great in Park. As soon as its put in Drive it almost Dies. Turning up the Idle screw still within proper Range for the Transfer Slot doesn't give sufficient Speed to correct Stalling. The Mixture Screws still work so I know I am not turning the speed Screw too far. Turning it any further gives excessive Idle speed in Park. This is the same problem I had with mine initially several Years ago. Float level is correct. I can't use the adjusting Screw on Secondaries because it is sealed. What if any is the effect of changing main Jets to bigger Size? I have 57's in it now and I have a couple of 60's to try if it has any affect on Idle? If the Idle Airbleeds are plugged from sitting around would that affect idle in drive? Any other suggestions? Timing is 10 BTDC with vacuum line off and plugged. Thanks

  

I read the Installation Instructions on the Holley Website. Part of what it says is to adjust the Primary and Secondary Throttle Plates equally which is not possible because the adjuster screw on Secondary is no longer adjustable.

  

The CARB may be EMISSIONS CALIBRATED where the usual adjustments are limited.

Maybe run the LIST NO through HOLLEY and see if a TECH SHEET shows up?

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Always check the transfer slot before installing a Holley.  It is the BASIC start to all adjustments of the start, idle, and idle speeds.  If it is hunting an idle rpm, then give it more slot showing, if it is idling too fast and you can't control it with the primary blades adjusted to closed, then decrease the slot.  .015" may work, but .018" may work better, it is something you have to actually adjust to find the best quality for your combination.  It doesn't matter if it is a 390 cfm carb, or a 1050 cfm carb, they will all respond the same way to basic tuning and idle quality unless you have one of the reverse idle circuit carbs.  Joe-JDC



JDC