Like many previous posters on the forum, I've had trouble setting up by 1976 CB 500 K1 after many years or sporadic activity/storage. It seemed that no sooner I had fixed one problem then another would appear, to a point where I was beginning to seriously fall out of love with a bike I have had for over 30 years.
Well thankfully that's all changed now.
To recap - my previous posts here and on FB had many helpful suggestions, mostly focussed on float levels which I had reset and then reset again when I hadn't done them properly.
Originally I'd thoroughly cleaned the carbs (only 8,000 miles NOS) and replaced all the O rings with a carb refurb kit as some had suffered from ethanol corrosion. As that didn't help things much I also decided to replace all the brass in the carbs with a pattern cardb refurb kit from fleabay.
A bit better but that was probably because I had by then fitted Dynatec electronic ignition and reset the tappets and cam chain and balanced the carbs.
The problem was the bike would start immediately with no choke and run beautifully until it had warmed up, when it would struggle and hesitate throughout the rev range, possibly running almost OK ¾ to full throttle. The plugs would be sooty pointing to too rich a mixture. Also it would start to pop and crackle with unburnt gases igniting in the pipes. Not good. I really didnt want to mess with jetting and needle heights, it just wasn't worn enough and everything is 100% stock, the problem must be in the setup.
After reading the Honda carb manual from the download section of the group I realised how important the relationship between the needle and needle jet were, and that they should treated as matched pairs (which it doesn't say). Also the easy starting from cold was a clue, it was as if the choke was on when it wasn't. Well I only changed the needle jets for the pattern ones, deciding to leave the original needles in place as it was a bit of a faff to change them. Also, the main jet replacement O rings I had fitted seemed slightly bigger than the ones on the pattern main jets from the kit which possibly made them not sit far enough into the carb body as designed.
That was my mistake!
Having progressively worked through every aspect of the carbs and taken them off more times than I could ever admit, I retrofitted all the original brass (jets etc.) and hey presto, it was brilliant! A long 50 mile run yesterday confirmed that, until I was stuck in traffic in town, when it started misfiring again. Once back on the open road it felt great again but by now I'm looking to get this perfect. One plug was sooty, all the rest were fine. I looked at the 4 pattern needle jets that I wasn't using and noticed one was slightly different. The holes in it were microscopically bigger (see photo) and the pattern needle didn't slide down into it as far and cleanly was the other three. I had only retrofitted 3 out of 4 needle jets.
So for what I hope is the final time for a while, I whipped off the carbs (10 minutes - a new pb) and replaced the needle jet for the sootty plug cylinder with the original, making a matched set and completely back to factory setting set of carbs. 20 minutes to replace them (those connectors to the airbox are always a fiddle) and after another test ride she runs perfectly with a set of four healthy clean plugs afterwards!
Phew.
So who knows if it would have been OK if I had replaced the needles as well as the needle jets, but I'm not about to try and find out. This has been a long a frustrating slog but now the bike has never run sweeter.
Not sure what the moral to this story is but I wanted to share it in case it helps someone else who like me was getting lost in chasing problems.
p.s. The original needle jet is the one on the right
