To get a full answer, you need to find a ref work on the different engines of the time. They came in a wonderfull and weird variety!!
Many rotaries drew the mixture in via the crankshaft. This was VERY rich and was mixed in the cylinder with air that came in via drilling at the base of the cylinder. Thus there was NO controll over these drillings.
LJK Setright's `Power to Fly' is a wonderfull place to get him started if you can find a copy.