AOTW, looking at the schematic, T1 and N1 will still control the opening and closing, but I think the main metering valve helps open it because of rapid acceleration (causes an increased fuel pressure). So it will still open and close as per normal but not open during rapid acceleration. I think helmet fire is right, and what is actually happening is that when emergency fuel is selected, the reference point that the bleed band opens an closes changes and the mechanical linkage from the N2 govenor (via the rocker shaft) re-references it back- I think!! I know it pretty hard to visualise without the schematic I'm using (I'd like to be able to scan it but its a hugh poster and I haven't got a scanner that big, plus all the detail would be lost) but i'll get there eventually. Thanks to everyone so far for the help. As a huey tech intructor, I'm embarressed that I don't know!