Not the needle, the jet. When you rebuild or dismanle the carb, assuming you have an HS6 with the fixed needle in the piston, then you need to centralise the jet.

If you look underneath the carb, where the adjustment nut is you'll see the jet assembly is held by a nut. The actual jet slides in a tube, it's the position of this tube you adjust. The hole in which the jet assembly sits allows for movement. You loosn the holding nut off and radially move the jet until the needle in the piston sits centrally in it. You can tell when its correct, the piston when decending should hit the bridge in the carb body with an audible thunk.

Other than physical damage, this is pretty much always the cause of the piston sticking. If the jet isn't centralised, but sort of OK the needle will wear the jet and you'll never get it to run properly. Its worth spending some time over. I reckon its impossible to do properly with the carb on the manifold, take it off.


Regards


Pete