Hi folks...motor is working great, but had some questunes on the T&T...my manual dosnet go in depth on how to work the old 'A' style, with the knob for 'engage' on the front. I remember other posts saying to leave the vent screw open, that it was self bleeding. Now, what does the 'engage' knob do, what position is it supposed to be in, and when do I turn it?<br /><br />thanks!