When using the single-vacuum distributor, the vacuum hose runs from the vacuum port on the left side of the carburetor to the vacuum canister on the distributor. In that case, the vacuum port on the rear of the carburetor must be plugged.
For most cool season grasses and for folks living in northern climates, the best time to plant grass is in late August, early September. Depending on exactly the climate you have and the type of grass seed you're planting.
Planting grass seed in Michigan can be done between the months of spring and fall but keep in mind that planting in spring may give grass a longer growing season in which to get well established, but the summer heat and weeds may cause problems.