Adjust the low end then, just screw it in a touch and see how it goes. The low end screw is quite exposed isnt it?....some carbs have them recessed inside the throttle barrel.
4 stroking is when the engine idles and sort of misses a beat every couple of seconds.
It sounds like you need to screw the low end in just a touch...otherwise you are there.
If you hover and punch the collective up if the engine bogs down then the main needle might be too rich....but dont get too involved. Its ok to run a bit rich...too lean will cause damage .
You must be about right with being able to touch the backplate, its a good indicator of whats going on.
If you notice a difference in performance after a half tank thats ok...and during the day the humidity might change and affect performance too...in either case you might need to land and adjust the MAIN needle...a click or two open or closed...not sure which as I havent run a nitro for a while...though will be doing so soon
Always use a filter on the fuel line, its not a bad idea to use a filter on the pressure line from the muffler to the tank...it keeps some of the rubbish out.
Dont get carried away with fuel tank acessories etc, keep the system simple...less to go wrong then.
Use good fuel tubing inside the tank for the clunk...and check it from time to time...make sure the clunk has a good gap between it and the tank end...too close can cause problems when you least want them.
Rob