If oyu are doing pulldowns properly,you shouldn't have hardly ANY feeling in your biceps. The point is to pull with your lats if you and I are on the same page here. Just using your arms as levers won't pump you up at all.....
that said, I found an UNGODLY pump by leading in with straight set concentration curls (Arnold style),straight set barbell/cambered bar curls, alt DB curls superset with close grip chins,preacher curls,then FINALLY 2 drop sets of Nautilus Machine curls....THAT pumps you so tight you'll need to shave at arms length for 3 days! Get an extension for your Machs and Schicks!