Mikuni TM28SS on an air cooled RD350

[2t Fan]

I am using RG250 GJ Mikuni TM28SS carbs on my RD350AC. Bike has a Dyna S ignition , UNI pod filters and Banshee reeds. Present set up is MJ-190 , PJ- 25, slide cutaway-2.0 , float valve-2.5 , Needle- 5DP39 , Needle jet 425-P-0 . What is the ball park jetting for such a bike ?  Bike shows some hesitation after 85km/hr. Plug is black oil fouled looks. Compression is around 125 psi in the left and 120 psi in the right cylinder.  if I want to use a leaner needle jet than 425-P-0 which one I should use ? Can I use 175-08 jet and 514 needle (OE RD350) on these carbs ?

thanks

[teazer]

I would start by just changing the needle.  P-0 is not a very large needle jet and changes won't make much difference at half throttle and above.  I don't have the dimensions of a 5DP39 needle, but look for one with the same root diameter and is thicker at the pointy end. 

5DP needles all have the same two taper angles, but the tapers start at different points, so they change fueling relative to each other.  For eaxmple 5DP2 tapers starts at 32mm where a 5DP7 starts at 26mm down, so the DP2 is overall much leaner than DP7