Following the warm welcome I received in the "Introduce Yourself" section, I thought I would provide an update on things I have discovered so far, with my '75 CB500K1.
(Firstly, many thanks to those who responded to my first post, especially Oddjob and Bryan, who have taken time to provide lots of info).
The bike landed in my garage on Monday 23 January, having been driven up from Kent by a pal from work, whose friend had rebuilt the bike in 2018 but he sadly became ill in 2019 and hasn't used the bike since then. On the face of it, the bike looks really nice, so I'm hopeful of a bit of a tickle-up in the garage (who isn't?) and we should be in business.
First thing was to give her a clean and determine which bits needed attention - she hasn't been ridden or cleaned since tackling a few laps of the Isle of Man in 2019 so there was a bit of road-splash but nothing too serious.
It was apparent that there was a bit of rust in the tank - not too bad, but worth some action. I drained the tank and although the fuel was quite orange, there was no jelly or black nasty stuff in there, just a few tiny flakes. I did some research and it seemed as though the easiest and potentially less problematic option was to try a citric acid solution and see what happened. I bought some citric acid powder online (it's about £6/kg) and mixed up enough at 1kg acid to 10 litres hot water and brimmed the tank, leaving it overnight to do its' stuff, then drained it and re-filled with the same and again left it overnight. I had read about "flash rust" appearing immediately following draining this from the tank, so mixed-up a litre or so of petrol with a dollop of 2-stroke oil ready to pour-in after emptying-out the acid solution.
I emptied the solution into a big white bucket and it was pleasing to see it had turned a bit orange and had some small flakey bits in it but no big lumps of anything. I shone a torch inside and it looked much better, so poured in the petrol/oil mix and sloshed it around for a while, then emptied it out, flushed with another half litre of neat petrol, then filled the tank with fresh Esso Supreme 99.
I drained each of the float-bowls and again, some slightly orange but clean petrol filled my little tin up, so rather than disturb the carbs, rubbers, airbox and all that lot, I instead crossed my fingers and remembered it's a Honda.
As mentioned in my Intro thread, the throttle and clutch cables seem quite stiff; the throttle cables had been passed down through the gap in the tank-side of the clocks then along the right side of the frame
, so last night I re-routed the throttle to make it run a bit easier; I sent it around the steering head, through the hole in the frame where the coils sit and on to the butterfly jobby - there is an improvement but the throttle still won't close on its own... further investigation required - I've got some WD40 silicone arriving today so hopefully a squirt of that might help; if not, I'll order some new cables. I'm not sure where I need to send the clutch cable yet so any advice gratefully received!
A new battery (together with 4 lites of mineral and an OE filter) arrived from DS earlier this week, so having popped the battery on charge on Tuesday, the temptation to give it try was too great to resist.... I had poured some light oil and several squirts of spray-lube down the plug holes a day or two after delivery and for a few days after, so having tried a few tentative gentle hand-prods on the kickstart with the plugs out during the last week, I was happy that everything was (hopefully) free.... I had cleaned and gapped the plugs while they were out and the previous owner installed electronic ignition, so I hooked it up last night, connected a temporary fuel supply, kicked it over a couple of times with fuel off, then fuel on, hit the button and she burst into life, immediately chiming-in on all four. As Captain Millyard might say, I was well pleased with that.
I'll warm her through over the weekend and change the oil & filter so everything is fresh.
The right hand pair of exhausts don't line up at the balancer pipe - I've read about bracket alignment being something of a dark art, so will have a look and see if I can suss-out what's wrong there. Failing that, I have got several hammers, so I'll sort it one way or another.
Again, any advice on this would be most welcome!
Anyway, that's plenty of rambling so I'll update if anything interesting happens over the weekend!
Bonjour for now, Phil.
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Must have shaken loose when I was hurrying along a bit on Saturday. Coincidentally I had to re-trace part of the route in the car later in the day and had a cursory hunt as I drove along but no luck. 
Wasn't really looking for another bike but a guy at work has a pal in Kent who restored the CB in 2018 but it's hardy been ridden since and he needed to get rid of it.