Honda-SOHC

Thanks yes I saw that section after I had posted my question 🤭 didn’t realise beforehand thought it was just for parts etc.

Well made some progress checked the continuity again on the coli and this time was making continuity ok between the yellow and green wires, found a slightly better but not exact wiring diagram for the bike and noticed the pink and green wires are terminate in a double socket at the battery end, there a corresponding green wire from the loom with a thick pink band around it which I had connected to the green wire in the double socket. So swapped the green with the pink band and connected it to the pink in the double socket and got one very weak spark. Tried a different spark plug and got a few more sparks but very weak and intermittent. Certainly starting to think the coil could be the problem having had that dodgy continuity issue then weak sparks when I could actually get a spark at all. Will check a few other things and see if I can finally get the correct wiring diagram. Thanks for all the help.

Ok did a quick check, there are 3 wires coming off the primary coil a pink, a green and a yellow.
According to the Haynes manual I have, the resistance (apologies if I’m using the wrong terminology) across the coil should be between 0.2 and 0.6 ohms. Mine is right on the top end at 0.6 ohms this is measured on the pink and green wires which are soldered to each end of the coil. Also get the same reading at the connector ends where they join the main wiring loom. The third wire (yellow) comes straight off the coil windings, and according to the Haynes manual there should be continuity between it and the green wire, I’m mostly getting an open circuit reading with that but occasionally a flicker of it trying to make a circuit. I need to find a better wiring diagram for the bike as the Haynes one doesn’t have a specific diagram for my model. However it does seem to suggest an issue with this coil.

Thanks for posting that link, very interesting.
I have checked for continuity, which it’s got, but I haven’t checked to see if the numbers are out with specification, off to do that now. 

Been thinking about selling my 1977 400/4, but not sure of what would be a fair price to ask for it.
Seen some really high prices being asked for what looks like show standard bikes. Mine is nothing like that though but I’d consider it as a survivor bike in good original condition. I’ve attached a picture and to be honest the picture does flatter it slightly it’s a few years old that snap and I have hardly ridden it since then so it’s a lost a bit of its sparkle.  Got a few scabs and scars on it and a bit of rusty staining appearing here and there on the chrome parts.
So I would be very interested to hear what your thoughts are. Bike has 27000 miles registered as a historic vehicle so no MOT required, rebuilt the carbs recently so runs ok but needs some fine tuning/balancing done, new oil and filters in the past week. Reason for selling is It isn’t getting the attention or use it deserves.

Many thanks for the replies I’ll give it a good oiling and if that doesn’t do the trick then a new cable it is.
Anyone had any experience with cable oilers? Always looked a bit gimmicky to me but might be an option.

Yep agree with all that I’ve used a t shape Allen key to push through from the airfilter box side to seat the middle two carbs but not got enough stretch in it to pull it back onto the oval duct.