OK,
The first thing I did was eliminate the DuBro Ezyfueler from the system. I think there may have been a slight, very slight, kink in that line somewhere but couldnt see it as its buried in the foam. A test flight revealed the same problems though less severe surging but none the less it was still there. Bubbles from the needle valve to the carb line also present, tiny tiny litle ones at WOT, and larger at lower throttle settings. Removing needle valve and putting a piece of fuel tubing over, and re-inserting produced way less bubbles but there were still some. Im suspecting leaking O-ring on the needle valve so a quick pack up and trip to the LHS, none in stock of course, but looking at another OS 50SX in the shop the o-ring is the same size (duh). Mine doesnt show any sign of damage anywhere and the LHS guy thinks Ive got other problems and suggests to reset the low end idle settings and top end mixture.
So a trip back to the field, wind the low end all the way in, then back out 1.5 turns, needle valve to 2 turns open and start er up. I let it idle for a minute with glo power still on then went to WOT (glo off) and set the needle valve to 4 clicks rich of peak. Back to idle for 20 secs and open it up, cough blubber and it runs, so shut down, in 1/8 of a turn on the low end. Restart and go to WOT and back to idle, let it idle for 20 or so secs and WOT, picks up smooth and clean. Some small bubbles were evident but didnt cause any rough running or surging. So off into the blue for an air test and it seems MUCH better, no surging at WOT, minor surging at mid range, pick up from idle in flight is good but is a little rough. BUT it doesnt 'seem' to be reving as hard as it did initially when it ran good. Vertical lines arent as long before running out of steam and it just sounds a little weak. Now the cowling is off so that could (probably is) be making a difference to its sound and maybe to its WOT full speed as well, it certainly seems to slow down quicker on approach to land without the cowl on.
Is there a better prop for this engine ? Will a 11.5x7 or 12x6 make it any better or worse ? I guess actually putting one on it and testing in-flight is the only way to really know.
I am much happier with it now and will wait until I can fly it again with the fuel dots system and cowling back on before I compain about it again

Thanks Edge guy, I checked on my return home this afternoon and its OK, no freeplay in the carb barrel.