My Moto Guzzi V50 uses twin Dell,Orto carbs VHB24 The mixture screw is out 1 1/2 turns this sets the tick over mixture If you go to the Amal web site there is a fault and tuning down load chart showing throttle postions and problem cures www.amalcarb.co.uk the main jet should on restrict fuel at full throttle slide/needle mid range and pilot mixture jet/screw setting at idle Hope this is a help