Hi!
Running as much as 25 % nitro in a sport engine is inviting trouble (to high combustion temperature due to the high percentage of nitro)
Use 5-10% nitro and your engine will run perfect! And a OS 8 or Enya 3 glowplug.
Setting the highspeed needle is the same as running the engine at fullthrottle...and at the same time... leaning the mixture out to max rpm (this way you should never fly because of problem with engine leaning out due to reduced fuel pressure when the tank empties).
A rewcounter (Tach)is very seldom needed for setting an engine be it sport or racing...learning to set an engine you do by ear! That's how we do it in pylonracing! And I thing most competitors do it.
Regards!
Jan K
Sweden