Progress so far...

Out of interest, what is the cylinder compression like?  And which coils did you replace the originals with?

I haven't checked the compression yet as my plan was to see what it was after the break in period but maybe I'll check that now .

I replaced the coils with CBX type as I saw many people on the site thought they were good replacements. I removed the resistor when I fitted the coils.

Have you checked your pickup coils for the ign I seem to remember that was a weak point on the 79's as the coils don't fire the cyl's beside each other maybe its an ign problem not a carb issue

wrote:

Thanks Kawboy. Ah ok...Funnily enough I do have one of Scotch's excellent cleaning tools and I did use it to clean the carbs. I must have missed something then. 

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I used carb cleaner as I couldn't find the recommended Lacquer thinner,  I'm in France, and every place I asked for it, I was given a funny look and a French shoulder shrug, followed by a shake of the head...as though I just asked them for a tin of "Dragon's sperm" or something.

This'll be the 3rd time the carbs will come off for cleaning...I'm glad I fitted those pod filters now.

We came across this problem once before and determined that "cellulose thinner" in the EU is the same as we in North America call "Lacquer thinner"

Since you've determined that the non firing cylinders are 5 and 6, the common element here is the carb.

The inability to get the bike to idle and it not going to idle immediately when the throttle is closed tells me that it's idling on the main circuit  and the main jets are dribbling fuel in to the throttle bores which at low velocity is extremely hard to control. hence the idle circuit. Once you get the idle circuit sorted out, things will smarten up.
 

Thanks. I haven't checked the pick up coils other than visually and doing the timing with the strobe. I'm not sure how to test them?

After some googling, I did also try asking for "Cellulose thinners" but they had never heard of that either. ( ...yeah).  It's all gone water based or is it water born? Either way they had never heard of it (they're the biggest/only paint suppliers in my area). Maybe I'll ave to just keep searching elsewhere for it then.

I agree, does point to being the carb as it's cylinder 5 and 6 but I had fluid/cleaner flowing through the idle circuits I don't know what else I could add to it. The cleaner was one I got at an auto parts place. here's a pic. It smells pretty nasty, allways a good sign.

When I backed the idle speed screw out, the revs did drop quickly again... to zero.

Each time I clean the carbs I just make them slightly worse than they were before.
I guess it's kill or cure...
 

Why not try going to a local auto body/paint shop and find out what they use to thin their paints like you say maybe they use a different name for their thinners.