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.
Pre-emergent herbicides kill crabgrass seedlings early in the growing season as they germinate. Pre-emergents are applied in the early spring, typically from March to May, or when soil temperatures have reached over 50 degrees for three or more consecutive days.