TOPIC:

Back from the garage where I performed the compression test.
120 PSI on #2 and 140 PSI on #1, #3 & #4.
Kind of surprised as I was so sure a lack of compression (thus of intake manifold) would have explain why no fuel seems to reach the cylinders...
What to do next???
I'll probably take the carbs apart again since they're not back on the bike yet. After this, I will install them back and use the starter fluid.
Will come back here to report the results.
Please continue to suggest the clueless member I curently am...
Thanks!

Check everything related to ignition.  Cam timing, if you have electronic ignition then check to see if it's correctly set and that the timing mechanism is correctly installed.  (Not backwards)

You say coils are properly wired but check them again anyway.  Check voltage at the coils.  Check primary and secondary windings for correct impedance.  If all is OK then move on to the fuel system.  Does fuel flow out the petcock on prime?  Is the hose to the carbs blocked?  Are the floats set correctly?  Do the float valves work?  

Just a few things I would check if it was my bike.

No success with starter fluid. A few back fires in the carbs and only one in the muffler...
Geez...
I love working on those old bikes. I rebuilt many calipers, master-cylinders, forks, carbs, etc. but with electronic/electric problems, I'm kind of in the bottom of a 12 feet high barrel with no escape. I vastly prefer mechanical problems. I'm done for today; will continue tomorrow.

Hardrockminer: Waht can be installed backwards please?

Are the spark plugs wires in the right ignition sequence? 

Claude. wrote:

No success with starter fluid. A few back fires in the carbs and only one in the muffler...
Geez...
I love working on those old bikes. I rebuilt many calipers, master-cylinders, forks, carbs, etc. but with electronic/electric problems, I'm kind of in the bottom of a 12 feet high barrel with no escape. I vastly prefer mechanical problems. I'm done for today; will continue tomorrow.

Hardrockminer: Waht can be installed backwards please?

It does sound like a timing issue if is firing out of sequence, you could try swopping the black and green coil wires - but firstly have you double checked the static ignition timing

Scirocco wrote:

Are the spark plugs wires in the right ignition sequence? 

You mean LH coil for cyl #1 & #4 and RH coil for #2 & #3? That's how they are wired.

Wookie58 wrote:

It does sound like a timing issue if is firing out of sequence, you could try swopping the black and green coil wires - but firstly have you double checked the static ignition timing

Yup, if nothing else works, I'll have to dig in that direction. But that's for tomorrow.
Thanks again for every comments guys!

Claude. wrote:

Wookie58 wrote:

First thing I would suggest is to measure the compressions to see if there is a problem, if you have the facilities you could rig up a "leakage tester" with an air line which would tell you conclusively where the pressure is going (if it is low) if you have to go the release oil route you only need a small amount (just enough to soak the rings) I have used WD40 in the past as you can direct where you squirt t but I am sure there will be endless suggestions of products. you can then remove the excess with a rag over the plug holes and spin the motor over (don't spin it with the plugs in before this stage as if you over did the oil you could hydraulic the motor and bend a rod) then put the plugs back in, the remains of the release oil will be burnt off as smoke out of the exhaust DON'T FORGET INCORRECT CAM TIMING WILL ALO SHOW AS LOW COMPRESSION

I do have an air compressor but no equipment for a leak test (don't know how to set this up anyway...). You can make a simple leak tester by welding an air line fitting into an old spark plug shell - when leak testing you set the engine to TDC on the cylinder you are testing, put the bike in gear, turn the compressor down to around 30psi and connect air line to the adaptor. You then listen- hissing in the exhaust means a leaking exhaust valve, hissing in the carb intakes means a leaking inlet valve and hissing from the crankcase breather/ oil filler means rings or bore wear. WARNING: Make sure the rear wheel is clear of the ground (when you attach the air line it can kick the motor which could pull the bike off the stand) if you have a helper get them to apply the rear brake when testing (in the car world we put them in gear and apply the E brake to stop the motor turning)
WD40? As simple as that? I was expecting a mix of Marvel mysterious oil and some other unobtainium product... If the motor was seized then these products would be required, however I am assuming your motor turns ok so you are simply trying to free a "stuck ring" which can be down to flash rust or carbon build up so WD40 will often work in these circumstances.
Does the engine need to be turned long to remove it? 10 secs or so should be enough (you can remove the rag and you will see if nothing more is coming out) Does the engine oil need to be replaced too after this? It would always be advisable to change the oil when you have introduced contaminants 
Thanks!

Your compressions look fine for a cold motor that hasn't run In a while but I have added some comments above just as an FYI

I'm not positive but I think the advancer, if you took it apart it can be assembled two ways.  I haven't had one apart for quite some time so this may not be possible.

hardrockminer wrote:

I'm not positive but I think the advancer, if you took it apart it can be assembled two ways.  I haven't had one apart for quite some time so this may not be possible.

The rotor can be installed 180 degrees out of phase.  In effect, switching the coils.  This can be tested easily by switching the coil wires.

YES! YES! YES! The engine is running!!

Yesterday, I removed the coils to take some ohm readings and all was OK. I then looked at the coils' brackets that I had painted and there was no bare steel for a good contact. I buffed away some paint and assembled back everything. There was strong spark (stronger than the day before) at the four plugs and I told myself: it will work!! End of yesterday.

Today, I put the fuel tank back in place and: Nothing! Geez, I was kind of desperate. Replaced the spark plugs. Nothing yet. Tried the starting fluid again: same result than yesterday (only a few backfires).

Back to head scratching telling myself that I would have to go through all the electronics to find a cause. It was a deception as all the old bikes I worked on have electronic ignition and they all worked perfectly so I was assuming all those parts were pretty reliable. It was time to change my mind now…

Thinking at Nessism comment, I told myself "why not invert the coils's wires. Naah, it won't work as the right colors are on the right coils". Having nothing to loose, I did so. And the engine started RIGHT AWAY!! What a relief. I don't know why I had to invert the wires but I'm so glad that I don't really care by now.

Once again, thanks a lot for every comment!! I really appreciate!

Good to hear you are sorted, FYI there is no electrical connection between the coil and the bracket or the frame ( only "heat transfer")