VP 5.7 Gi, 2012 c/w raw water cooling - timing and hard starting

[Eagle Spirit]

My engine has backfired through the flame arrester several times now. I am experiencing hard starting, it does start but often during the cranking I have to crank several times, and often it will backfire through the flame arrester once I have stopped cranking for 6-8 sec. So I am thinking that the timing needs to be adjusted. Yes, I have changed out the plugs, replaced the cap and rotor, and removed and the re-installed the wire set. I admit, I did mix up the number three and five wires. The engine did start, but only for 2sec. Switched the wires to where they are supposed to be and it started ran ok. Went back to the boat on a nice hot afternoon and she started a-ok. Went back to boat during the evening and it would not start. Seems to be taking several cycles of cranking before it starts, but now there is an audible knock in the engine at idle....possibly spark knock?

Anyways, any feedback would be great,and much appreciated.

Would I need a scanner to check and set the timing on a 2012?

What would be the correct timing degrees?