How many miles as your TMX done. I say this as over time,as my TMX on a TS1 got richer and richer and I ended up with a 58 needle on 2nd clip and a 17.5 pilot. Did plug chops and colour was OK through rev range and did 2 coast to coast with this setting. However, in reality, I was compensating for the needles and fixed atomiser wearing with use.
So for this years Euro rally, and after talking to Andy Francis, I went back to the recommended 20 pilot and 56 needle on 2 clip. Really boggy between 1/4 and 1/2 throttle, in fact it was hard work getting through those revs. But after 1/2 throttle, ran great.
At the rally, I bought a brand new 35TMX from Andy Francis and put in the recommended setting of
22.5 pilot
310 Main jet
56 needle on 2 clip
and it ran a treat all through the rev range with a great plug colour.
Well it did run OK till I blew a hole in the piston just outside Eindhoven, but that was due to an air leak with my inlet manifold.
So the point of this story is that your Mikuni may be that worn that you are finding it difficult to get the correct setting, as I had been doing.