Thanks everybody for your inputs and sugestions.
this is the fuel im using:
manufacturer: morgan fuel
says on the bottle: omega 5% f-om-5, castor/syntetic model engine fuel

according the tag on the bottle; what are the content or characteristics of this fuel?
what 5% means that? what is the amount of blend content?
is this fuel good for 4 stroke engines?
should i add something extra to this fuel? if yes, what?
thanks again.