Can somebody help me about my problem please. So after about 1 and a half hours riding my gasgas trial i felt that the power of the engine became less that is less speed (was about 5th gear) but i continued driving it for about 1 more hour until i arrived home. As i turned it off and let it cool down for some time i tried starting again but wouldn't start. The bike sort of lost its compression and the kick start became more easy to  push down. I cleaned the spark plug but still didn't start. Tried to start it 1 week after and its not starting. Is it maybe the reed valves or the silencer leaking air? thanks for your help. 

Is very possible that a ring has nipped up, take off the head and barrel and check to see if the ring has picked up bit of ally. 

thanks i will try.

 

Is this bike new to you and when you say “less speed in fifth” what speeds had you been doing. From your description when riding the engine was trying to seize up or nip up as some would say. It appears from your description that you have overheated the engine, possibly a coolant issue. Excessive down hill runs with throttle shut will starve piston and rings of oil, possibly causing the rings to eat the cylinder bore and scuff the piston ring land area. You might not have used the correct fuel and oil mix ratio. If you are lucky it might only be a blown head gasket, but then some compression would leak into the cooling system and cause coolant to be forced out of the overflow or rad cap (model not known). Not certain if your bike has a cooling fan but this may not be working and could be the causal effect. Hope you can sort the problem ?