I would invest in a temp gauge[ TT0 ] about £25. its the best way to jet and run new bored /tuned 2 strokes, , I "v been jetting my DT400
, and have dropped from 190 main to 150. , and dot let anyone tell you the air screw and pilot affects ONLY , idle and 1/8 THROTTLE.
, I turned air screw in 1/4 turn, and running speed temp dropped 20 degree F, . get the sensor to suit your spark plug size , [12mm / 14mm]
heres a link, [ usa] but you get them in UK,.[ search]
http://www.ebay.co.uk/itm/Trail-Tech-TTO-Temperature-Meter-Digital-Gauge-14mm-Spark-Plug-Sensor-72-ET3-NEW-/381631066379?hash=item58dafbf10b:m:mMuD7UU-217AkY5q9559__A