Mask the carb opening real good.

Remove any obvious grease and dirt with simple green, etc.

Scotch brite pad any loose paint off until you have a solid substrate.

Clean again and again with wax and grease remover until you know it's clean.

Mask everything you don't want paint overspray on.

If you have a shop vac you can place the hose near where your painting and it will vacuum up any overspray floating in the air.

Any hard to reach spots can be lightly painted with a brush first and then painted over with the aerosol can or paint gun.