Here is an excellent 4-stroke Baja dirt bike carburetor for dirt bikes with 49cc, 50cc, and 70cc engines. The carburetor is compatible with the Baja DR49, Baja DR70 Dirt Runner, and the Baja Warrior WR49.
The mounting hole spacing is 1-15/16" (48 mm) center to center with 5/16" (8 mm) through holes.
But it keeps getting better! Monster Scooter Parts gives you a choice of configurations for this carb. You can order it either with or without a 35mm Air Filter