How to be idle

[Billington]

My 1930s BSA runs okay but if I close the throttle it dies. The bike is has a Amal 6/122 carburettor which has a Throttle stop adjusting screw and a Pilot Air/Adjusting screw.



I understand the purpose of these are as follows:

THROTTLE STOP SCREW. Set this screw to prop the throttle open sufficiently to keep the engine running when the twist grip is shut off.

PILOT AIR SCREW. This screw regulates the strength of the mixture for idling and for the initial opening of the throttle. The screw controls the suction on the pilot petrol jet by metering the amount of air that mixes with the petrol.

I’m hope you can help me with a good method for setting up the closed throttle idle. I was thinking about starting the bike up with the Throttle stop screw full screwed in, then taking it for a short ride to warm it up. After this unscrew the Throttle stop screw until the engine beings to stall then turn it back in until a smooth running is achieve.

After this I may experiment with the pilot air screw by turning it first in then our until a slow continues tick over is achieved. 
Does this sound about right or is there an authordox method.

Thank you for any help

[john.k]

The simplest way to set idle is to hold engine speed as desired by the hand controll,then simply wind up the carb screw until the revs rise........you will also feel the spring pressure disappear as the slide is raised by the screw.......then nip up the locknut...............you should note ,some bikes are setup to die as the grip is closed ,because they dont have a magneto cutout,stopping button that works........so owners prefer the engine to stop if they should fall off.

[iansoady]

.... but I would expect the BSA to have a valve lifter which is the normal way of stopping the engine. It was usually only Villiers runabouts that shut off completely.

What model is it?