did you check for an air leak on the inlet using a spray ?
Even an extremely small leak would have a profound effect on your mixture .!
To test the mixture is correct before and after changing jets and atomisers you need to run the engine up to temperature then apply a little choke at idle, 1/4 throttle 1/2 throttle 3/4 throttle and WOT .
Each of these checks will tell you what needs to be changed ie pilot jet, atomiser or main jet.
(The last 2x checks need to be done quickly to avoid stressing the engine too much.)
If you don't make these checks at each throttle opening you'll just be changing jets at random and learning nothing.
What should happen is the engine should immediately bog down ie too rich.
If the engine continues to run normally or it momentarily picks up revs a little then the mixture is too weak
at that particualar throttle setting .so then you will know exactly what is working correcly and what needs to be changed.
Your mixture does not stay the same throughout the rev range,.... it is determined by a combination of things at each part of the throttle opening
Did Allstyles tell you which atomiser they were supplying ???ie 5899-2 etc ??
edit looks like Allstyles drill a 5899-2 out from 1.75mm to 2mm which is basically the same as a standard 5899-5 except the idle fuel and air holes are different .
If that is the only difference you can buy micro drills on ebay and drill your own 5889-2 atomisers and experiment with say 1.8mm 1.9mm and 2mm etc