you don't need 20:1 after the break-in. I do 32:1 and it runs great. Checked the spark plug at that mixture and it was slightly tan/brown. that's exactly where you want it to be. in my opinion 20:1 is too rich.
Your opinion may not be right.
As I mentioned in the other thread, my engine's instructions recommended 16:1 for break-in, then 20:1 thereafter.
I've stuck to that for 510km and
never had an oily plug or any problems, once the carb was tuned correctly.
Although, again, as I said in the other thread, 32:1 won't do any harm and is OK to run, it is really too little oil for these badly manufactured, poor tolerance engines. There's a good reason that the manufacturer suggests 16:1 then 20:1. If the plug oils up or is black, the fuel/air mixture is at fault,
not the fuel/oil ratio.
The 'slightly tan/brown' plug that you mention tells you that the fuel/air mixture is about right,
not the fuel/oil ratio.
Rich/lean is always used to refer to the fuel/air mixture,
not the fuel/oil ratio. By saying '20:1 is too rich', you're confusing the issue.
skipS, it sounds like it might possibly be running a bit rich at WOT. Most of these engines do if there are no air leaks. If this is the case, the answer is a smaller main jet. The slide needle only has effect up to 3/4 throttle, then the main jet takes over.
Is it 4-stroking at WOT?
What colour is the plug?
You might need to do a WOT plug chop.
There's a bit more info in
NT carb tuning basics.