i have a 80cc 2 stroke. I ride it regularly. just after riding it, i went inside for a few hours and came out to start it. It only fires with the choke up, as soon as flick it down its just cranking and not firing, when i give it the throttle with the choke down it changes tone quite a bit but doesnt fire . I was first drawn to a carb problem,i checked for spark with placing it on head,and it sparked. The carb was clean, i blew through each jet,and theres nothing obstructing. I changed the spark plug, wire, and soldered connections, could it be spark ? too much resistance,e.g it fires outside, but not inside. i cant get my head around it, within a few hours it can develop a problem like this, fires quite nice with the choke up. ANY SOLUTIONS ?