A few Issues-fuel /electric with my 78 2H9.

[excess.11]

You can test continuity of the Pick up coils at the tci plug in connections. You can gently tug on the wires down on the left of the engine where the timing indicator/pointer is located.

[Aussiexs11]

Thanks, so far, 4 solid , reasonable responses. I will have a look at each one. 
The fuel cap is interesting, as I even tried opening the tank cap when it wouldnt start thinking it may be an issue. Didnt help, but I will check the vent none the less.
The TCI, yes I will also look at changing. Ive been monitoring the battery voltages, with a charge unit connected , the battery is new, and has been holding 12 plus volts, and I notice when bike has started the charger indicates 13 plus volts (to 14 volts)
The fuse block may end up with a newer push in fuse unit as per the units Ive fitted to my Ducatis. They are the pinicale is horrible fuse arrangements! Ive seen the original replacements but think why replace with older technology?
Coils are something I definately think may be an issue. Will need to research where these pick up coil connections are, its been a while since I looked!

Thanks gents.

[excess.11]

Replace the tci unit.......if you have a spare.......the intermittent faults at differing conditions point to it breaking down.

[Eveready1100]

Grant, the first place I'd look would be the fuel cap vent, as they do have a habit of blocking up and starving the motor for fuel after it's been running for some time.
Here's a link to a thread about pulling the cap apart to check - click

One other thing that you mention about the backfire indeed points to the electrics, as while you're cranking the bike, the starter is using most of the power of the battery, but when the starter button's released, the ignition unit suddenly gets enough power to fire(about 11.3 volts or something) , resulting in all the unburnt fuel that's gone through the carbs while cranking to ignite hence the bang.
On that point, I'd first check the battery's condition both before and during attempting to start the motor to see if it's still up to the task. If it's consistently doing it (a quick check would be to jumper the bike battery with a car battery to see if it still does it)
Also,  a suspect fuse block needs replacing as it's the achilles heel of the stock electrical system and will not get any better over time.

[Aussiexs11]

Hi All,
Its been a while since my last post.... Ive been busy working away and racing my Ducati..., and my poor XS has managed to be ridden sporadically, but reasonably regularly at least, but.... I have noticed a few issues developing and it culminated with a near freezing ride home through the mountains on what seemed like 2 cylinders on saturday,so, this has caused me to raise a few questions and get some feedback from you all. BEFORE i start the strip down, and analysis of the bike.
OK: The Bike is my 78 2H9 engined XS
Recent History: Has had a full top end rebuild and bores honed /new rings, new cam chain, new clutch  etc less than 5 k ago (thats now nearly 2 years). Shim clearances etc were adjusted then, and not too noisy in the top end, all should be pretty good there.

Issues:
1. Started with the bike just electrically cutting out when idling when I have stopped or was negotiating a turn. Would restart after a few seconds of button push.
2. Developed the habit of not wanting to hold idle after I had ridden for a while (say coming down to Sydney from mountains)
3. Then developed the habit of just not wanting to start at all, would wind over, using full choke- nothing, so I would leave it, come back a while later or even next afternoon, try half choke- nothing. and so on even no choke- nothing, I tried switching the kill switch off /on a few times, got a backfire and then believe it or not, bike would start.
Did the same as above trying turning ignition off and on instead of using kill switch - got same backfire and same start would happen event?
4. Then once started, and riding along with a warm engine (because miraculously the bike would idle nicely on the full then half then no choke), I got from the Nth Shore back to Lawson (say 100klms) and the bike cuts out and sounds like a big bang crank R1, growling away on what I can only think was at least 2 cylinders. (Tacho held revs as normal?). So, I slowed down, back gears, and found that when I went back to 1st, nearly stopped, (close to idle speed), the "miss" would clear, and away we went, business as usual. UNTIL about 15 klms further along when it did it again. So I reduced speed and limped home (as I was not far then).
I get home, leave the bike in driveway in disgust, go back to it to put it in shed , thumb starter and it fires on all 4??

So, I have now gone to the spares cupboard in preparation, got all my spare carby bits out, got my spare igniter box out (2H7 unit) , and am preparing to remove body /tank and start checking /pulling apart/cleaning etc- whatever it takes.

My thinking on this-
It could be timing? But why idle so well at times??
It could be coils?? or a coil pack breaking down?
It could be kill switch (but I am doubting it as it still runs at least on 2)
It could be carbys full of crap and needing a good clearout?
Would the ignition box cause this??
Maybe there is a breakdown in wiring somewhere in coil /ignition circuit- Any idea there??

So I wonder if any of you have had this experience? The cutting out when riding worries me , thats not much fun if I am on highway amongst the traffic we have and I lose power, then it wont start again...

I cant even look at the bike till next weekend as I work away during the week, but would love some ideas.
Im going to put a new fuse box in as well as when I looked at the original it just looks old, and well, like it needs better contacts, all fuses are OK, but the fuse clips are weak. (an age thing I think.) There is no corrosion etc on wires /fuses though (I am an eleco)

Hope you gents can assist me. (anyone have spare coil packs I think thats worth a try?)

Im just not sure, and I am certainly open to ideas, the bike has a solid maintenance history,

regards
Grant