Hi, My 2008 Future 4rt 300 (Wiggys old bike) once warmed up starts to release an uninterrupted (even with revs) & continuous jet of steam from the top valve cover breather hose (a drip of water forms approx every 10 seconds from the condensate forming in the hose). First thought it was head gasket so replaced this, no luck, so I then swapped a complete top end from a standard 250 working bike (apart from leaving on the aftermarket S3 barrel & piston which all looked fine) & ran it twice for about 25 minutes (not ridden just on tick-over with a few revs of the throttle) & both times it boiled up within 3 minutes, fan kicks in as normal, engine sounds normal, no steam from bottom crankcase breather or radiator, no white smoke from exhaust, water pump impeller fine & both engine & transmission oils still perfect with no sign of water & oil emulsifying.
With the standard 250 valve head now fitted the only difference with this Future bike to a standard one is a small brass decompression valve (reducers engine brake) fitted to crankcase just below barrel (probably similar to what Honda fitted as standard from 2014 onward).
A long-shot but has anyone had a similar issue or may know the cause? Thanks in advance.