Welcome to the wonderful world of 510 owners.
Does it still have a points type distributor?
As someone else said, 1 1/2 years is not that long.
I would pull the hose from the fuel filter (front corner of engine compartment) that goes to the fuel pump and stick it in a can of fresh gas. Then make sure you have a good battery. Next pull the air cleaner and put a little fresh gas in the carb and then see if it will start. If it does not start, pull a spark plug and see if it is getting spark. If no spark, pop the cap on the dizzy and check the points.
That car should start if it was running when parked.
Check out the following sites for good 510 info:
http://www.the510realm.com
http://www.dimequarterly.com
http://www.ratsun.net
http://www.datsun510.com
Good luck with the new 510.