Check your Datsun owner's manual.

Typically you need not to 'key' it several times, but instead, pump the accelerator pedal several times and key once. Maybe one pump for warm days, and four pumps for cold days (near 0 degrees).

After the car sits for several days, BEFORE you crank the engine, check the fuel bowl site-glass. Perhaps you'll find the fuel bowl is empty. In this case you need to crank the engine for a while to pump fuel to the engine before it will start. You can fix this by fixing the leak.

Another possibility is that your auto-choke is not working right, it should close 100% on the first pump. That can be adjusted very simply.