Haytor Harrier 41 running problems help please?

Hi I have a old haytor harrier 41 quantum engine ( electric start autodrive ) It has been playing up alot of late ie running very rough ie hunting I think you call it ) I have stripped and cleaned the carb It now runs OK for about 10 min then starts hunting again stops is difficult to start but when it does it runs ok again for a while then smae procedure. Any ideas ??

Thanks in advance for any help regards
Mike