Idle problem with #4

Hello,
I just bought a '78 650 SR and after having had the carbs out twice for cleaning, I've found that it generally runs o.k. except cylinder #4 header doesn't warm up while idling, but put the choke on and it heats up to the same temp. as the rest.
Compression is the same as the rest, for good measure I've replaced 1-4 coil with another that tests good; spark is strong with the plug out.
The brass tube that extends down into the float bowl for the enricher is snapped off flush with the carb body.
I've cleaned the pilot circuit from air jet to air screw to pilot jet to carb bore.
Since #4 header warms up with the choke on, can I assume the enricher will work without that tube?
Since #4 header won't warm up at idle without the choke(the others do) and the pilot circuit is clear, what else is there?
I've almost cased this thing; please help!
I'm in saskatchewan, Canada.