Ruby throttle hesitation.

[Nick Salmon]

In my experience, whilst the slow running needle screw makes relatively little difference to tickover, it does have a marked effect on whether or not the engine picks up cleanly when the throttle is opened. I would warm the engine then with it still running turn the screw right down. It may stall. Back it off a quarter turn restart and test throttle response. If it doesn't pick up cleanly unscrew the needle another quarter turn and try again. The optimum position is almost always within about a half and one and a half turns.