CB750 K2-K3 - help! no spark!

[Pitt]

Hey,

So I've got an early 1973 Honda CB750, it appears to be some sort of construction joke since the front part of the bike is a K2 and the rest a K3, combined with some modern mods. I bought the bike half a year ago but need to sell it again because I'm leaving the country! so the pressure is on!

when I got the bike it was running but then the electrical circuit broke on me about 3 months ago and would just first slowly loose power (gas problem) then get to a stop and refuse to turn on again. (but that's a different story)
I replaced the wiring harness because it was falling apart. I've got it all more or less hooked up now (some funky connections because of the K2/K3 mix of parts), Lights, indicators, honk, starter motor all work, but I have no spark on any of the four plugs!
I checked the spark plugs by taking them out and holding them close to the engine's metal casing while starting the bike. nothing. Tried with new plugs, still nothing.
The bike got a modern Dyna ignition system which replaced the old points. So I don't suspect a problem there.
Also I find it very unlikely for the two ignition coils to break at the same time.

So that would boil it down to either the whole cabling (although I am pretty confident the ignition circuit is correct) or the rectifier. (that's at least what some forums claim)

Now my questions are:
- is there anyone around who has experience working on those cross-over K2-K3 models?
- how do I check the rectifier? (I don't have an oscilloscope lying around unfortunately)
- anyone got experience with the Dyna DS1-2 ignition system in a K3?
- what am i missing?  

cheers,
Pitt

[TOOLS1]

Welcome to the forum. Hate to hear you must sell your bike.
The first thing to do is hold the spark plug against the engine when checking, for spark. The plugs will not fire unless they are grounded. Then check the black/white wire that goes to the coils, for power. If you have power there, then check the power wire to the Dyna ing. There should be a wire coming from it that goes to a switched power source (red wire, and it can be connected to the black/white wire).
Hope this helps. TOOLS

[Pitt]

Hey Tools,

thanks for the help! I will check it out as soon as I can and post here again.
Life is a bit hectic right now so might take a day or three.

Cheers,
Pitt