[Michael C Henry]

If it's any help now. Quick Fuel Technology has a vacume secondary housing that has a needle valve incorperated in the housing.It's to control how fast the secondaries open. I've seen a newer version in the Car Craft mag that has the needle valve screw incorperated into the anodized cover .I'm using the older Quick Fuel Tech vacume secondary housing with the needle screw in the housing it's self,and a quick spring change cover.I sent my carbs to quick fuel Tech and had them redo them ( two 600 cfm 1850 holleys) . I had ordered the new housings earlier but hadn't installed them. They installed a small tube into the carbrueter main body , that accsess vacume from the primary away from the ventury wall edge under the booster.You'll see it in my gallery, it's not very large . They said they installed the purple springs. The way I understand it's the spring that determines when and the screw determines how fast the vacume secondaries open . They describe the operation should seem smooth and not a hesitation and a surge .