We have a brand new world formula on my sons kart. Went through the break in procedure, tuned the carb in, and it was running and sounding great. Tried to start it up today after a couple weeks of sitting and it would not start or stay running unless I was giving it throttle. Took the carb apart and sprayed carb cleaner through everything but had the same result. Not sure what else to do and kind of baffled on what could have changed. Advice is much appreciated