I'm w/ Dave on this one.  I would borrow a carb from someone, and swap it out. 
This will atleast rule out the carb.   
Then go onto wires.  This is if it is just those 3 cyl fouling every time.  There isnt to much after the plugs and wires that would only affect 3 cyc.     
The other thing is not to change to much at once w/o testing between each time. 
I know it sounds like common sense, but that has burnt me when working on problem w/ my camaro.   
Good luck w/ it.