Holley vacuum secondary, or is it mechanical

[Paul G]

In the pic you can see a small bolt in the secondary slide arm. It forces the secondary open with throttle position. I have a 727. Would it be beneficial to remove the screw?

[alcusswhen]

A lot of people including me put the screw there to over come the weak vacum that comes with a big cam. But with an automatic yours [if you keep it] needs to be in the middle of the slot to give some progression to the linkage. And to make up for no secondary pump. You can buy weaker springs to tune your secondaries to your engine vacum. It looks better that way but don't work any better.

[Runner]

A lot of people including me put the screw there to over come the weak vacum that comes with a big cam. But with an automatic yours [if you keep it] needs to be in the middle of the slot to give some progression to the linkage. And to make up for no secondary pump. You can buy weaker springs to tune your secondaries to your engine vacum. It looks better that way but don't work any better.

    the secondaries open from a vacuum signal on the prinary side,   its from air drawn through the carb, not vacuum that the engine might be loosing at idle from a big cam.   my take on this is,  if you want mechanical secondaries then put a double pumper on it. if your not happy with the speed that the secondaries open then put a weaker spring in, or buy a quick fuel secondary kit, they remove the check ball from the vacuum diaphram housing and put a needle and seat type adjustment in so you can adjust how fast the secondaries open with the turn of a screw.

[Ghoste]

   The spring kits are cheap.  Not as cheap as a screw but  .

[471_Magnum]

It is a common misconception that the function of that mechanism is to override the opening rate of the secondaries. Not true.

It is actually to limit the opening rate, and pull them shut.

That carb has been hacked.