engine bogging down?

Well here it goes--I start my bike it usually fires right up and idles great at first. I go and run it around the block a few times and bring it back to mess with it. I leave it idling for awhile and then it starts to want to die. after a few minutes it does. then you cant start it without choking it, even then it still does not want to. This is the second time it has done this. It sat for about three weeks without being fired up but it also did this last time a did. Any ideas or suggestions.

Valve clearances recently checked? Thinking maybe too tight and getting tighter as engine warms so as to lose compression.

Well I bought this bike two months ago and have been fixing it up. As far as I know nothing has been checked. I really dont know too much about motorcycles this is the first. When I first got it, it didnt do this. How would I go about checking the valve clearance? after getting it running a added a fuel treatment/cleaner thing to the gas, could this have anything to do with it?

any other thoughts?

Check the screen and inlet tubes on the
fuel petcock.

check the vent in the fuel cap, it might be plugged up, also have you put a new fuel filter in.
valves, go to wiredgeorges site he has a real good section on checking the valves

Guess you didn't like Patton's suggestion to check your valves. I suggest you not only check your valves but perform a full tune up per a factory service manual. This is an old vehicle and it requires regular attention and maintenance. I suggest a good starting point would be to check the valve clearances and compression.

I actually wanted to check the valves I just didint know how, thanks for the link bskz650. It has a brand new petcock on it so I dont think it is that. Also has new plugs and wires. I have not done the new fuel filter so I might just go ahead and change that out.