I,m going to refer you back to Amateur's suggestion that you look at the two rubber tubes that connect the carbs to the boost bottle. I even recommend that you put new ones on because they are probably dried out and have split, or are about to. If either one splits , air will enter, and cause the problems you are describing.
The factory settup is a alum. tube that the hoses attach to, with the boost bottle the normal curv of the tubes is changed slightly which will put a little extra pressure on the tubes, causing one or both to split if they get dried out.