I agree with Mustangman.
When you get the idle about right, throttle respons is good when the engine warms up, and worse with cool engine.
tweak the needle little by little. !/4 turn may be waaaay too much.
Finally, get some plugs of the same brand, in different heat ranges, and check out which performs best.
then maybe change brand, and do it all over again. OS#8 and OS-F are good plugs to start with. Novarossie #6 and #5 are quite good as well, Enya #3 and #4. Just a few of my suggestions.
This is tedious work, I know, but perseverance never failed anyone.