Carburator settings

If you have played with them the only way is to get it going pretty well is" ....
find the idle screw - usually larger - and turn in 1/2 a turn - hopefully that will keep it running - then find the 'slow' running screw turn it in until it stops then turn out 1 and 1/2 turns. Leave the fast one alone.
Get it started then adjust idle screw so its faaster if need be.,, now slowly turn the 'slow' screw in then out say 1/2 turn and listen for it either speeding up or slowing down leave it at the point where it sounds ok and try giveing a few 1/2 speed rev ups. If it goes back and idles as before - leave it.

The fast screw... (first make sure your exhaust outlet is totally unblocked - the slightest restriction here will cause it to never run right at high speed). Start it up and then try full throttle - same thing as before try adjust the fast screw first in a little then out until it runs well at what seems the faster speed it can - then check that it accelerates well from idle to full speed. If not adjust it a little more until it does.
Once it will idle ok and return to idle and also run full speed, then you can back off the idle screw until it will idle without the chain racing arond the bar.

Bear in mind th chain wil be racing around while you adjust it so keep fingers kids and idiots well away..because you are adjusting it with that chain moving..