CB 500 K1 running issue

[Sesman]

I’d say the idle circuits are clear.

[K2-K6]

I’d say the idle circuits are clear.

Does seem positive from that report.

Beefington, have you tried setting the idle circuit as per Honda manual to optimise the carbs as they stand now?

It involves warmed engine, then winding outward individually ( successive carbs) until the rpm reaches a peak with that cylinder, then just as it starts to falter from mixture going too lean, turn it back inward to drop the rpm by 100. Then reset overall tickover speed with main control and move to next carb. Complete all four and that should be a reference setting for your engine equipped with those carbs and jets. This routine should establish if the very slow running is able to work correctly.

[Beefington1975]

I’d say the idle circuits are clear.

Does seem positive from that report.

Beefington, have you tried setting the idle circuit as per Honda manual to optimise the carbs as they stand now?

It involves warmed engine, then winding outward individually ( successive carbs) until the rpm reaches a peak with that cylinder, then just as it starts to falter from mixture going too lean, turn it back inward to drop the rpm by 100. Then reset overall tickover speed with main control and move to next carb. Complete all four and that should be a reference setting for your engine equipped with those carbs and jets. This routine should establish if the very slow running is able to work correctly.

I haven't tried that. Will do tomorrow and report back. Thank you

[Beefington1975]

My latest fiddlings suggest that the bike is running too rich a mixture at idle - brand new plugs covered in soot after just a few minutes of running. Is this the root cause? Or a symptom?

[McCabe-Thiele (Ted)]

I'm no expert - far from it - I would judge how rich or lean an engine is running  after say a ten mile ride - when engine has cooled check the plug  colours.

[K2-K6]

If started on choke they'll be fairly black, should get lighter after some running if it's ok.

Basics though, choke open and close fully without impairment?  Air filter ok/clean/new ? Just to check the obvious.

Moving on, what do you have the idle adjustment mixture screws set to now ?

[Beefington1975]

I'm no expert - far from it - I would judge how rich or lean an engine is running  after say a ten mile ride - when engine has cooled check the plug  colours.

I wish it would run long enough to ride 10 miles!

[Beefington1975]

If started on choke they'll be fairly black, should get lighter after some running if it's ok.

Basics though, choke open and close fully without impairment?  Air filter ok/clean/new ? Just to check the obvious.

Moving on, what do you have the idle adjustment mixture screws set to now ?

Hi. I didn't need to use the choke to start the bike. Ran the bike long enough to perform the check you described. Have to be honest and say that the changes in rpm were very slight so not sure I got the screws spot on. The are set to about 1.5 turns out.

The air filter isn't new, but looks good (not that old). The choke opens and closes easily and fully

Many thanks

[K2-K6]

Try with the screws set at 2 1/2 turns out and see if that gives anything in the way of sensible running, or improvement at all.

It does appear to be too rich.

Do you know which size of idle jet is fitted to them ?

More rudimentary check is to remove air filter and see if that improves running.

Really just trying to get further assessment to help indicate what may be out of kilter.

[Beefington1975]

Try with the screws set at 2 1/2 turns out and see if that gives anything in the way of sensible running, or improvement at all.

It does appear to be too rich.

Do you know which size of idle jet is fitted to them ?

More rudimentary check is to remove air filter and see if that improves running.

Really just trying to get further assessment to help indicate what may be out of kilter.

The idle jets are 40s. I'll try the aircrews at 2.5 turns out and take it for a spin (won't be able to do this for a couple of days though).  Many thanks for the help so far.

[Sesman]

Must admit. Turning the air screws on mine makes little if any difference to the engine rpm.

[Beefington1975]

Just a thought...saw someone on another thread suggest that engine oil level could be a factor? I've checked mine and it's on the top line. The deposits on the plugs look dry, but could the fouling be due to excess oil???

[deltarider]

What exactly is sooted? The thread's end? That's normal. Focus on the plugs nose, the ceramic insulator that is. Realise the CB500s plugs soot very easy at idle. Back then we used to ride these bikes. Nowadays and in this forum in particular, more and more owners seem interested in having a perfect idle they can listen to sitting in a deckchair.

[McCabe-Thiele (Ted)]

Just a thought...saw someone on another thread suggest that engine oil level could be a factor? I've checked mine and it's on the top line. The deposits on the plugs look dry, but could the fouling be due to excess oil???

I would only expect a high oil level to become an issue at high engine rpm due to excessive oil misting

[Beefington1975]

What exactly is sooted? The thread's end? That's normal. Focus on the plugs nose, the ceramic insulator that is. Realise the CB500s plugs soot very easy at idle. Back then we used to ride these bikes. Nowadays and in this forum in particular, more and more owners seem interested in having a perfect idle they can listen to sitting in a deckchair.

Both the centre and end electrodes are sooted. Listening to it from a deck chair is not my aim...but it is all that's possible at the moment. It won't even make the move from 0 to 2 mph without cutting out.