B40 cuts out when I open the throttle from tickover

[dougc]

Engine runs ok, coughs a little on tickover when I open the throttle even very slightly and slowly it cuts out but starts again easily on the net kick.

[rhyatt]

Initially , I'd suggest the transition between the idle circuit air screw and the air slide.
Have you been through the carb

[V500]

I'd suggest a quick-and-dirty test of trying it with half choke and seeing what happens. If it has no choke I would try raising the needle and retrying it.

[iansoady]

That transition is governed by the throttle slide cutaway. I've found that many bikes prefer a slightly richer (ie lower number) than originally specified, possibly because of modern fuels.

[Derek996]

From my experience that suggests a slightly weak pilot mixture. Try screwing the idle mix screw in by ⅛ to a ¼ turn to see if that improves it. You may have adjust the throttle stop screw slightly to get the desired idle speed.