300 mile service on Roketa 54B

[4getful2]

As far as i can tell by your plug and my old eyes, it looks to be just a skosh lean.
It looks like the electrode has gotten hot, unless it's my view of the picture.
They've got those things set so lean for emissions and fuel economy, it's no wonder they run hot(predetonation)
If the fuel screw isn't out to 1 1/2-1 3/4 turns out ,you should try it and see how it starts with the engine warmed up. The fuel screw works from idle 'til about 2000 rpm, after that the needle starts to move up, then from 3/4 throttle to full throttle is when the main jet works.
If you're wanting to get into the jetting thing, go for the quickest and max speed(main jet selection)first, then go for the drivability-needle adjust and fuel mix adjustment.You'll kill 2 or three hours doing this but be glad you did after it's done.
Check the valve adjustment before you do this as since you have a low mileage unit, it may have never been checked.