There are three distinct circuits in the RS carb, each of which is designed to cover a different throttle range. The Main covers top 1/4, the needle from about 1/4 to 3/4, and the pilot first 1/4 (these are quarters of full throttle turn).

If one of them is off, you often end up leaning another one out to compensate. Based on your mileage, it sounds like either your main or your needle is off. Based on the number of turns your PMS screw is out, it might be the main (needle lean to compensate). This is just a guess though.

You should start with the main. Test it using the WOT test (tech tips - stock carb). If it is good (little to no change in acceleration when backing off - be sure to read the article), then you can probably assume your needle clip position needs to be adjusted.

You need to start with the main, since changing it changes everything else.

Do you know what main, and what needle clip position the dealer set you up for?

Do you still get backfire on decel at 4 1/2 turns on the PMS? Look out for this far out, the PMS screw can vibrate completely out...

Also, what air kit, exhaust, is AIS intact, is manifold ported, and does your exhaust system still have the baffles ??

GRAM