its not that hard to examine jets for blockages, just hold them up to the light and use a magnifying glass if necessary.
in the past i have see filter gauzes actually in the carb feed pipe spigot, so thats worth checking also.
if there is a drain plug on the bottom of the bowl, take it off and see if fuel pours out there when you switch on the tap
Theres a strong possibility that all you need is new crank seals though, as you said it runs on high revs for a short while, this is typical behaviour from a worn seal magneto side.
You have picked a difficult subject with the RS200, no haynes manual, no parts list to be found either