Senior Tech Team
Join Date: Jul 2002
Location: The Centennial State
Re: Holley Carbs Idle Adjustment
The RI screws have fat heads, BUT the more important part is that they look differently than the standard idle screw at the NEEDLE end. The standard screws are long and slender, while the RI screws are more blunt tipped and short. Holley might be making a fat head standard screw now, so it might be worth it to confirm they will work before ordering.
One thing you should check is to see if there is a number on the metering block somewhere that matches your carb list number. People sometimes swap them with other Holleys, but they don't interchange. If you're metering block isn't "numbers matching", it will never idle right. Square and spreadbore metering blocks are two different animals (idle system).
If you are using long slender ended mixture screws, the reason why your car is not idling right is that its running too lean. It's getting the set amount of gas, but it's also getting too much air. WHen the blunt ended RI screw is in there, it cuts off more air due to it's fatter end, which makes the mixture richer.
If you're putting this carb on a mild engine, it really should work fine. Like any other carb, it takes a little time to set it up right and correct the mistakes of previous owners.
"The man who lets a leader prescribe his course is a wreck being towed to the scrap heap."