it will fire up just a bit hard, but thats not the main problem. i dont think 15% will make it run a whole lot better than 5%. i dont know it just wouldnt stay running, just kept cutting out even with tuning. another problem is, and im not sure how big it is, i cant re locate my fuel tank, in the avistar its in a fixed spot. the centerline of the tank is lower than what st book calls for compared to the high speed needle. i called a guy from a hobbytown usa and he said not to run any glow powered engine under 40 degrees Fairenheight. but people here say they run them in much colder weather, this sucks, the engine has 1 gallon thru it and its broken in. just not too long ago when it ran ok when it was warmer but still had the midrange problem if i left the throttle just under half and let it sit there.