Thanks for the reply MX360.

Ive been working through the ignition system, double checking all I can.
Don’t see any way to test the CDI but all else seems fine.
In lower light conditions looks to be great spark at the plug!
That was great advice, I’ll work through as noted.
Initially did put some fuel down the plug hole to check for fire and it didn’t do a thing, checking for lack of fuel!

One thing I noticed and it has me hunting a fuel issue is as follows. On assembly, I placed the fuel over flow tube that comes off of the bottom of the carb bowl onto the upper carb venting nipple, to make a loop, just temporarily.
I noticed it had fuel in it, up to a static level but I didn’t pay much attention to it.
As I think now, the fuel level would have to be either too high or the tube in the carb has a leak internally allowing it to flow out. If the level is that high it seems it could flood it. But I’m not sure this could cause it to be so “dead” without any hit at all. I checked but I hadn’t seen a sign of over flooding when checking, who knows.
I can’t believe it would be an internal leak as it has all new Yamaha crank, seals and bearings, all went together nicely.
 

Yep no good like that & could cause a vacuum stopping floats to drop if no other vent on the other side of the carb body. Let that vent hang down. If it spills fuel there's a float valve or float issue. But as you say, it should still show signs of life. 

Is the plug getting wet.

Put a small screwdriver into the plug cap terminal.  Place the steel screwdriver shaft 6mm from a head fin with paint scraped off.
if the spark jumps 6mm you got healthy spark.

If it does not, remove plug cap and place bare ht lead 6mm from a clean fin. If it jumps 6mm you have a bad cap.  If it doesnt, you have a bad coil or poor connection between coil and cdi.

If you have a visible timed spark, as you assert, I do not see it being the LT side or cdi.  But still a possibility.  Rotor magnetism... But weak or intermittent spark I go for the HT side first.

After checking it appears that the MX175 shares much of its magneto assembly with the MX100 and the later RT100.

You say has good spark late in post #1 [B​​​​ike seems to have good spark] & cdi spark never looks good but you wouldn't want a belt off it. So appart from a shorted out oily plug shorted from burnt on oil--which it won't be if it's not yet run, then i'd look elsewhere. Happy to be proven wrong though!!.