Pulling my hair out

I had a very similar sounding problem with my 340. To make a long story short, I knew that the car wasn't preforming right.....seemed to be holding back, stalling out, sputtering, etc (you get the picture). Ended up that my linkage from the transmission was to short (because of the highrise intake) and this caused the throttle to be open prematurely........thus poorly running engine. I added about a 3" section to the passing gear rod at the carb & about the same amount from the tranny up to the passing gear pivot. This made the throttle plates come to their proper place and NOW, the fine tuning of the carb made all the difference in the world in it's running!! :thumbup:
Don't know if this is your situation or not, but a quick look down the throat of the carb should tell you if the plates are open too much or not.
Hope this helps.
Greg............mtn_jake