strange on start up

hi, just sum background my ped has not been on road for a few month as mot ran out etc but i still run it for a few min each day... anyway recently i noticed when i start it up after its been left for like a day it revs its balls off on its own so i turn the idle down a notch then back to its original position (as it was on start up) then the ped idles fine at a low rpm and will run fine. what could this be? cheers

 

uh oh air leak

or just the choke working lol

 

oh soz a didnt say theres no choke. (used 2 run fine without choke)

 

air leak then or over rich