Did you just put the car away or did you put some kind of oil in the motor for the month it sat. If it sat in a humid place and rusted, it way be harder to get going and may need maintenance. I would change the plug and try to richen the motor. Especially if it was lean at the last race. Go 1/2 turn on the bottom and 1/4 turn on top. try to start with this and see if it helps.

DJ Apolaro