According to a KTM bulletin for 2006 models, .3 L. You can view the bulletin here: http://74.125.95.132/search?q=cache:rFOyaY4tY0EJ:www.ktmriders.nl/modules/downloads/KTM%2520Engine%2520Oil%2520Recommendation.pdf+gear+oil+for+a+KTM+65SX&hl=en&ct=clnk&cd=3&gl=us
KTM recommends Motorex Top Speed 4T 15W50.
Transmission oil Motorex, SAE 15W-50
250 cc
240 ML of 5w fork oil.
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KTM recommends .5L of Motorex Top Speed 4T15W50.
.7 L
40-1 is what i would run 50-1 is what AMSOIL recommends. Less smoke, cleaner plugs, great lubrication. Use what the manufacturer of the oil says for your application. That would be 50:1 with AMSOIL Dominator or Interceptor 2 cycle oil.
I am assuming you mean gear oil, KTM recommends .7L of Motorex Top Speed 4T 15W50.
.7 L