You might take out the idle mixture screws and shoot a healthy 3 second blast of starting fluid or brake kleen into each port then replace the screws. First counting the # of turns CW in to lightly seated before removing them will let you do this (effective in alot of cases) test in 2 minutes cuz you can quickly return them to their original position(s). the idle circuits are the smallest passages in the carb & dirt in the fuel will make that system act up the quickest