It's sezed but I'll take a look at it the weekend,
What should I be looking for when I open the over flo, how hi should the fuel rise to

Is it possible to find this valve that is assembled in the right cover? It retains the oil coming from the pump in the way to the filter.
Thank you all

Hi there, yes you will find it after taking off the clutch cover, it is quite obvious.

After starting the engine, the oil pressure generated by the oil pump will push it open to allow oil to flow to the engine, and after shutting off the engine it will retain some oil i the oil lines and channels to the crankshaft/piston and cylinder head. If the ball valve is leaking, the oil will seep out from the oil pump, and the engine will have to fill up the oil filter housing at the next start before oil gets delivered to the lubrication points. Much more annoyingly the oil tank will drain into the motor block, leaving the oil tank "obviously" empty, so new riders will top up a liter of engine oil, and overfill the engine. The excess oil can be found in the air filter later, having caused all kinds of issues.

On engines with dry sump lubrication system like the single cylinder Yamaha enduros, always always check the oil level during a ride and not before a ride. Most conveniently this is done every 300 km when filling fuel ....

Andy