Banshee engine

He's right, if you look the intakes are down and back of the cyls. I believe that would be a case reed intake. some sno-mo engines use it.
 
It could be a TZR250 parallel liquid cooled twin. Possibly an RD250LC.

I'm not sure if either of those are case reed valved or not but it's possible.
 
Update: If that is a 250cc engine, it's a TZR250. The first version of the engine was a YPVS liquid cooled parallel twin with case reed valves. It had to fit in a backbone frame for a race bike so the carbs were low...
 
yamaha claims 50 BHP @ 10,000RPM. The idea was a road going race bike but that number seems a bit inflated for a stock trim engine that was designed to last any kind of time