Causes of unsteady idle/WTB heater control valve?

[MopaR&D]

I got two questions here... First, I recently built a 360 Magnum for my '70 Duster which runs GREAT except for a bit of an unsteady idle. I've made sure the initial timing is correct (~10* BTDC) and played around with the idle mixture/speed but it still seems to fluctuate by about 100 RPM and my vacuum gauge goes down by about 0.5-1" every couple seconds; it's not really steady just every 2-3 seconds the engine slows down a teeny bit then speeds back up. I only have about 200 miles on the engine which has a new bottom end, is this normal for a fresh engine to do? Specs are 10.5:1 static comp, Lunati Voodoo 60401 cam, Air-Gap intake, and Carter AFB 625 cfm carb.

Second question, this same car came with A/C from the factory and has a control valve which shuts off flow to the heater core when the heater is turned off. Mine started leaking so I just bypassed it for now but would still like the functionality in warmer weather since it no longer has A/C and the cabin gets pretty hot with the heater core always 'on'. Where can I get a new one of these, they seem kinda hard to find?

 

[pishta]

Could it be a lean surge? Richen the mix by a 1/2 turn on both sides and see if it makes a difference, its free, and reversible.

 

[rklein383]

I always suspect a vacuum leak first.

 

[MopaR&D]

I think you were right the idle mixture was too lean, I turned the screws out bit by bit and it seemed to run smooth. I have a new big problem though; I just drove to another town about an hour away and I nailed the gas once on a back road. When I let off the gas and slowed down to turn the engine started to run really rough. I checked the ignition system and it seems to be OK, I feel like it's the carb because it only runs rough at low speed/just off idle; if you give it enough gas it accelerates smoothly with no misfiring. What should I look for?

EDIT: No vacuum leaks either I checked all that over