Sorry, not sure if I have placed these questions in the correct area!

Background,
Three year restoration project with my son, using 99% Yamaha parts. This is not an enduro!

Bored .30 over, new crank(Yamaha), reed components(Yamaha), rod (Aftermarket),  piston (Weisco) all new bearings, seals gaskets (Yamaha).

Carburetor was rebuilt( Yamaha parts)
Ignition system was not changed, is original. 
Yesterday was the initial start up on the completed bike.
No start.

Scope of issue,
B​​​​ike seems to have good spark at the plug when pulled but zero indications of fire.
Plug pulled, premix added to top of piston, zero indication of fire, Air box cover removed, along with cleaner and Either added, zero indication of fire.
Top cyl compression at 80psi.

Could the CDI fire at the wrong time?
Any place I could find a proper wiring diagram, don’t trust the Clymer, one I have, found too many typos..

Is the flywheel key present?  Did you line up the timing marks on the stator to the ones on the crankcase?

Edit.  Forget timing marks, appears the 1980 on motor has a non adjustable stator.

Greetings from Tennessee USA  
  Did you try a different spark plug I’ve seen 
​​​​​​  new spark plugs that wouldn’t fire under compression 
  

CDI box plugs directly into the stator on the "dirt bike" (USA) version MX175.  The Black/white from CDI goes to kill switch.  That's it.

As I've mentioned in previous posts, I've seen quite a few...  the majority in fact... of the USA MX175 stator/flywheels be bad. 

Do they spark?  Yes
Do they run? Sometimes, but if they run they have odd issues like they miss or won't rev up.

CDI box is the same as the DT175 and I've swapped those around with "known good" and they run the same...  problem seems to be in the stator or flywheel which is different/smaller than the DT175 version. 

I certainly was looking for any timing marks when building the engine but didn’t see any indication of needing to line anything up, except the flywheel to the key.
The stator went in the exact same place, based off of witness marks.

I shouldn't ask but did you forget the crank seals, no suck no go or if it went in then won't send it up top to go bang. Ok I read back & seals in sorry. Flywheel key you ok'd. 80psi it be trying to go. Leave the exhaust of & see if it sounds hopeful, like can hear it trying. Not just hopelessly flooded up in which case hold it on full song & kick. Could tow it but be careful the throttle is fully safe & shutting right down & back out the throttle stop screw so you can hear the slide tough down. Welcome if you're new.

Yes, sure did!

Ok,
Iv’e heard that the “Dirt bike” stator versions were problematic.
Unfortunately the bike didn’t run when we purchased it, the ignition system was the only thing not played with.
Ive run some resistance checks through the stator, seems to fall into specs.

The secondary side of the coil though may not!
Though I’m not confident the book is right?
says 6.0 ohms at 60 deg, we have 12.0.
 

You say you have good spark so i'd start looking elseware. Piston not back to front with windows to the exhaust. Sorry i thought i'd throw that in as have seen it done. & i'm out of ideas. Would probably try to run like that with plenty of hand choke over the carb mouth.

"B​​​​ike seems to have good spark at the plug when pulled but zero indications of fire.."

Do you see gas leaking out of the exhaust header? Is the plug wet after kicking it over a few times? Is gas seeping from the stator- side crank seal? It has been my experience with has spark but wont fire issues is that there is some wrong with the carb and/or leaking crank seals. The pilot jet, choke, or a number of things in the carb could be an issue.
Ignition or fuel or combinations of both. Turn the fuel off, take the plug out and kick it bunch of times to blow out the gas. Let it air out a bit. Check the spark again a few times in the dark and make sure it is consistent. If you are satisfied that that looks good then put the plug back in. Close the choke, close the throttle, turn the gas on and give it a moment. Keeping the throttle closed, carefully find top dead center on the kick lever and give it a smart kick. Do it again slowly couple more times. Open and close the throttle. Then kick again. If nothing happens, pull the carb and check it.
Leaky cranks seals, carb issues; floats sticking, flaky ignitions...drive you crazy, I have battled with then all. I usually go through a few carb bodies until I built one up that is reliable. Replaced the cranks seals, and end up installing electronic ignition on all of my bikes. This is just me and my experiences but I have been there with spark but no fire many times.