but right now engine cranks but no start up... trying to figure out why
Things to check:
Make sure you're getting fuel:
-Something could have clogged the system. Check your fuel filter(s) and carbs.
-The Facet (or so it looks) fuel pump could have died (it looks fairly old). Getting a fuel pressure gauge, even just a cheap in-line one for the engine bay, can help a lot when trying to eliminate possible issues related to fueling.
Make sure you have spark:
-Check your plugs and make sure they're not fouled.
-Check the signal wires coming from the distributor (Red and green on my Z's L28), they could have got fried.
-Make sure a plug or coil wire hasn't fried. It happened on my brother's Jeep once and we only found out after a good bit of trouble shooting due to not thinking to check.
-Make sure the coil is actually generating a spark.
I can't really tell from the picture, but make sure you have the chokes hooked up. It may be less of an issue with Mikunis, but when I got my Z it didn't have the choke on the SUs hooked up and it made cold starts take forever (a couple of minutes or so). Once I got a choke hooked up, even though it's just on one of the carbs, the car starts right up, even when it's cold.
Good luck with it! Old Nissans are nice cars to learn on. My Z has certainly taught me a good lot.