Honda-SOHC

Just curious. What's the stamped on number on your carbs?

Always start with the simplest and check the ignition (all items) and doublecheck before you move to the carbs. What plugs do you use and what's the gap?
https://www.youtube.com/watch?v=t3cuvGVwnjI
Left condensor (1+4) is bad, right condensor (2+3) is good. Condensors seem to go bad when warm.

Floatlevels have to be checked. Where's your CB500 from? Yanks had the needles in 4th (combined with the airscrew 2 turns out, at least that's what an American Honda booklist says). In Europe we had the needles in 3rd and airscrews 1 turn out. What main jets are in? Is there a cover over the airfiltercase? A forgotten cloth?

If the bearing retainer isn't tight then you will get sprocket float as the entire cush drive is moving around, best get that sorted ASAP as the chain may come off if it gets to a certain point.

Thanks again. So the retainer needs to lie flush (is that the word?)

I read this thread with interest. On my CB500 I discovered there's some play that causes the part (flange final drive?) on which the rearsprocket sits to move a mm or so out of the hub when rotated and because it is irregular it causes a not nice running drivechain. I haven't figured out what exactly is the origin. I seem to remember having seen that the collar rear wheel side was irregularly worn (but... because of what???) and having seen some iron dust there. Could that collar somehow be the culprit. Is there a possibility to help this with a washer somewhere?

I think about 50% of the bikes I own(ed), mostly the cb500 and 550s had some sort of gap issue on the rear wheel and swing arm but beyond bunging in the odd washer to keep it all alighned I have never let it bother me, often the swing arm flexes in a few mm when I tighten the rear spindle, as long as it ends up in line the bike handles fine, passes mot's etc, if fussed about the washers being unsightly, measure the spacers plus washers, get someone with a lathe to turn up a spacer the right length

I wonder if Matthewmosse recognises my problem. Dealers are not much help: one said there should be a third bearing somewhere and another I talked to on the phone said I needed a new flange and they're bloody expensive. Help is appreciated.

Possible air leaks between carbs and head? O-rings between head and intake manifold are always suspect.

The 76 550 was the best of the 500/550 series IMO. I suppose it is a USA import. I'd replace those US handlebars immediately for the better bars that were on the European models.

Every time I see a picture of our lovely bikes equipped with the higher US handlebars, I'm shocked. How could Honda equip a perfect riding machine with this silly sit up and beg bars? They simply cannot offer the correct riding position, period. Here's my guess: it is as Honda knew there was an extra market to have: people that have enough money to buy a new toy but are afraid of riding. This in a market where a licence to ride a motorcycle is very easy/cheap to get. Maybe Honda estimated there were a lot of big belly's too, I don't know. Unless you have a fat belly (why not have a chopper?) every one should have the lower bars, for better control and THUS safety.
Decades ago I've removed the rubber of the pegs to gain an extra cm or two for my legs. No need to be afraid: not once did my feet slip of the metal pegs, not even when I was standing on them in terrain.
The best you can do to your bike (and yourself) is making the bike fit well.

If somebody could scan it and mail it to me to complete my collection, I'd be very grateful. I used to buy Classic Motorcycle Mechanics but it has vanished from our shops in Holland years ago. I have several old articles in foresaid magazine however.