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.
When to Apply: Apply in early spring to prevent crabgrass all season long. For most areas this is going to be from early March until mid May. So it can vary from March 1st-May 20th. Crabgrass seeds can germinate when nighttime soil temperatures reach over 50 degrees for 3 days.