Hi
Just saw your post & I guess you've sorted it by now, but anyway the bike (240 Rotax) was fitted with an AMAL 2627 carb, with settings as follows:
Slide '22' - yes 22 - this was a special slide for armstrong and it's just a 2.0 filed a bit to make it 1/2 way between 2.0 and 2.5
Needle 2B1
Needle jet 106
Pilot jet 20
Main jet 130
Spec. L2627/1
I have tried both a new AMAL and a new Dellorto and the AMAL seemed better. However, to get the engine to pull well at the bottom end it was necessary to retard the ign. timing to the most retarded position as specified in the SWM 240TL manual ( I don't think Armstrong ever made a manual for this bike ??). Otherwise it's a nice bike.
'hope this helps
John