blaster not running right please help

Ok so i live in Kansas and its 11 degrees outside fired it up and rode for about 10 mins and then i stopped and it revved up and would not die had to choke it to kill it now when i fire it up it idles down slow again

airleak or lean jetting for those temps =
leakdon test,
readjust airscrew (turn in to richen it) to highest idle,
and jump 2-3 sizes up on main jet, in those temps.
 
Is there a good dirtbike motor i can put in this blaster without a whole lot of mods i cant get this motor running right to save my life
 
And you could be plagued with engine mount cracking vibrations, a lot of dirt bike motors are not balanced very well.