and no, it’s not only setting the fueling screw right…

the order of arrangement in term of modifications. from most important to less

1. Spring
2. Needle
3. Oil and damper

1. Spring
   depression rate
   blue, red, yellow and green
   don’t stretch them! then you’re adjusting the whole rev range while changing them don’t effect pressure at light throttle.
   the spring gives the range the carburetor works in.
   how to choose them; at full power the spring and so the carburetor piston needs to be on the top of it’s range
   if too strong, piston will rise but not all the way. power is decreased. will become too rich as a first and then too lean in the top end as a result of not rising all the way
   if too low, piston will rise too fast, and goes to lean
   a stronger spring will make te needle richer so that’s why this needs to be addressed first.
2. Needle
   needle chart which tells needle stages
   needle graph which indicates you what the effect gives; as small changes in the lower range give big effects and big changes in the higher rpm’s give way less effect. difference is from about 12 percent at stage 3 to nearly 1,5 percent at stage 13
   So it’s better to change the needle if possible
   HS4 = 0.090 inch diameter
   position 3 till 6 are important for throttle pick up and cruising conditions
3. oil and damper
   makes it run richer on acceleration but also makes it fall fast enough so it can use the vacuüm to pick up again
   available oils:
   jack oil 8w32
   20w50
   SU own oil SAE 20
   10W40
   ATF which is around SAE 20

extra’s
Vacuüm is needed for road cars but not for race cars as they don’t run on the same rpms for longer times.
about 16 till 20 degrees maximum

bad running engine checks:
-check for vacuüm leaks, especially around the inlet on the engine
-spark plugs, do they fire? you may check by loosing one while the engine is running or go and try change them anyway
-measure compression, and if your doing this and press to discharge the air out of the meter and moisturized air comes out it might be water or petrol.
-choke not coming back in, it might be the choke being stuck so it keeps running rich
-damper stuck or heavy, check if it moves and comes back again easily

sources
https://www.youtube.com/watch?v=b2y486A5j6A