Carb Jets

[Jez]

Hi, Thank you for all the welcome messages, i could do with some expert info please, my Honda cb 500 four is from South Africa & i am trying to get it running right, it is a 1975 D Silver helped  me identify some parts i required from the frame number a CB 500K1four 72.It has a four into one exhaust and foam air filter pods, the main jets i think have number 78 on is this right ? And would i be better putting 100 size main jets  in please any help would be appreciated.

               Cheers Jez

[Bryanj]

Something found over many years is you will never get it to run properly all the way through the rev range with pods. Jetting is pure experiment.

[matthewmosse]

I tried running pods, hopless on my bike I found. Got it perfect one day, bit of rain or frost and it was unrideable. Far too succeptable to weather.  As for pods and snow, dont even ask. Took 1/2 hour to get it to start. I was impressed by a genuine K&n filter that took the place of the stock airbox but retained the standard phlenem chamber. That definitely liberated a few extra horses and saved cash over the standard Honda filters. You couldn't tell it was fitted unless you lifted the tool tray.

[deltarider]

I was impressed by a genuine K&n filter that took the place of the stock airbox but retained the standard phlenem chamber. ... You couldn't tell it was fitted unless you lifted the tool tray.

Matthew, that oval filter (102mm) by K&N is about the only filter I seriously considered buying back then. The code was R 82 (R 83 for the 550) but maybe that was just the code the Dutch importer had given them. But I didn't do it, partly because I didn't like to mess with oil, where I can change a stock air cleaner element within 12 seconds. Secondly one could expect a lot more intake noise and I wasn't sure if it didn't require rejetting.
Talking about intake noise, if you find #78 main jets in your CB500 carbs, they most probably will have the stamped in number 649A on the flange and the airfilter box originally came with a lid, snorkle, air duct whatever you want to call it. UK, France and the US did not have that air duct. They had the 627B carbs with #100 main jets, but there were some differences in setting. I'm pretty confident that in France and the UK, the jet needle was in 3^rd (middle) slot and the airscrews were advised to have at one turn out ± ¹/₈. What I've learned from a American Honda booklet is that they had the airscrews 2 turns out and had this compensated by raising the needle one slot (4^th). That we (Holland, Germany and other European countries) had the air duct, probably had to do with rules on intake noise. I have a standard airfilter and experimented with #100 main jets in combination with the removal of the air duct. It brought nothing but more intake noise. My experience matched what Germans had also found when they had done the same experiment.
So Jez, you may have a look at the carb number (see the pic where it is located), but if you run pods, the #78 main jets will almost certainly have the engine run too lean. So either return to stock or go #100 main jets or maybe even a bit more.

[matthewmosse]

The jetting etc was all set by last owner luckily for me, but to get it all right I think I am going to have to re fit the exhaust it came with which is loud, as in louder than my lazer 4 into 1. It was an awesome setup like that, very responsive and a fair bit more power. Looked sweet too, 1970's rocket 3 raygun silencer onto a bsm 4 into 1 collector. Lovely chrome, only took it off to preserve it from commuting road salt over winter, and to run the 550k3 carbs, I know they get a bad rep, but when sorted they are wonderfully frugal. I've never looked at what carbs they are or what jets it's running. If the carbs overflowed I just gave a shot of redex.