Im trying to figure out what this piece of linkage controlls on my carb.
I notice that when i tighten the nut in the picture my car doesnt bog as much on take off.

But overtime the nut loosens and causes bogging again. Is there a specific setting that the nut should be set to? Do i need some sort of locking nut for it?

What does it control exactly? I hear squirtying when i tighten it so im assuming fuel?

Here it is

 

thats your accelerater pump. it shoots extra fuel to help with pulling out etc etc. look at the holley tuning guide. you can use a feeler gauge to adjust it but i cant recall the number of the top of my head.

 

Adjust it by pushing on the lever on the bottom by hand, as far down as it will go; then open the throttles to WOT; then adjust the nut so that there's .050" of distance between the screw head and the pushed-down link at WOT. You just want to make sure that it won't quite bottom the lever out at WOT because that will bend stuff.

At idle, there should be NO GAP WHATSOEVER. The lever should in fact be partly pushed. Gas should begin getting shot out of the pump squirters with THE TINIEST motion of the throttles off idle.

To lock the nut, just go to the hardware store and get a 2nd nut, and put it on top of the adjusting lock nut.

THe spring controls the pump shot duration, in conjunction with the squirter size and pump volume. Large squirters = shorter shot with higher volume.