Ok first off it's not mine it's a friends, and it goes between 20-30 mins then totaly stalls and wont even show signs of life for the next few minutes. After that the only way to start it is to open up the choke all the way then soon it will die again but be alot longer before it will restart. it's always the exact same senario, it started doing it about a month ago and it's been getting worse. is it possible that it's losing compression when it gets warm? though it should be fully warm after a few minutes. Allways has a full tank, it's not the fuel and the spark plug was just replaced. One more thing, it makes aweird loud slow clicking noise every now and then in the front right area. it's very hard to pinpont because it only does this when moving. Theres no sticks or debris, we carefully inspected it for that. Thanks ahead for any replies and your time!

man the only thing I can come up with is the valve adjustment. or the timimg chain.   but with it getting hot then stalling I would loom at valve advjustment first.