Maynard,
That sounds exectly like a problem a friend of mine had with an older trike a few years back. It also ran a silvertop 582.
If it was not so serious it would have been funny to watch his trike reach 100ft AGL, loose power and start descending, then he'd squeeze his fuel primer bulb, briefly get power back and start going up again, then down again, etc, etc. His engine also ran flawlessly in ground test runs.
I think I remember it being that the circlips on his carburettor needles were in the wrong position by one groove.
I have taken the liberty to email the text from your first post in this thread to him for his feedback and am trying to entice him to come to the Goulburn airport BBQ again on 22nd Dec.
He's also a self employed mechanic.
Cheers,
Glen