At low idle pinch the fuel line. If it just fades and dies you are lean - turn the low/idle idle screw counterclockwise 1/8 turn. If after about four seconds it speeds up before dying you are adjusted well for most conditions. If after longer than four seconds it speeds up before dying you are rich - turn the low/idle screw in 1/8 turn clockwise. (The one on the opposite side of the throttle arm).

Take it to half-throttle for a few second and idle down each time between tests to get a good fuel flow going.

High end is different - that's the larger needle-valve.

I run a TT Pro-46 and it is a splendid engine. Mine accumulated enough dirt knaps that the needle arm housing was damaged and allowed air to leak in. It was impossible to tune for a good idle (or mid-range transition for that matter). I replaced the stock carb with a Perry carb and it is still going strong.