Remove that bolt, and put a lighter spring in. You also in all likelihood need to lean out the accelerator pump. The fact that you can mechanically open the secondaries and not bog indicates the pump shot was far too rich to begin with. It was too much for just the primaries, but is ok for all 4 barrels.

In other words, the carb wasn't set right.

 

loads of good explanation here

my take on this is: if you have to manipulate your carb to have it run better then something was wrong in the first place. so yes. change the carb back to original and go from there

 

One more point, get rid of that air cleaner! One backfire through the carb and they have been known to catch on fire. Also, they degrade over time and bits of foam get sucked into your engine.

 

+1 on the air cleaner. I had a Holley and one of those air cleaners and caught it on fire.

I changed to a Carter AFB and a chrome air cleaner. I still have the Holley, but haven't used it since.