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.
Depending on where you live, the best time to plant grass may be in the summer months. Warm season grasses need to be planted in the summer since they require warm soil temperatures to germinate and grow. Otherwise if planted in the fall like cool season grasses are, they may still germinate but will most likely fail to make it through the winter season because they will not establish. With proper seedbed preparation and other care practices, you will find it is fairly easy to plant grass seed in the summer.