Honda-SOHC

For some reason it seems to be getting just a little excess fuel at the very low end of carb range.

Setting the screws out further will not change the metered fuel from idle jets at their maximum (roughly half way through carb opening) as that's controlled by the 40 sized orifice. What the air modulation does is to change the "ramp" angle leading to that point by bleeding more air through than fuel at the very base of throttle slide opening.
Honda don't state an absolute for this setting of air jet, more a competent start point to be refined during setup. Obviously this case you can see the response from resetting them (indicating circuits are working reasonably) and ending up at 2.5 out is probably at the far end of range reality, but not unworkable. Probably more assessment is valid here to see if you've any unwanted complications and perhaps see if anything else is out of the ordinary over further mileage.
At least if it runs well you've got a chance to now get more comprehensive view.

The inline filters, I'd definitely not associate with low speed fuel demand and feel confident to discount those in this area of carburetor work. Usually it's peak flow that is of concern with these and inadequate supply volume to replenish float chambers fast enough when flat out and wide open throttle.  The float chamber of course acts a constant reservoir to the jets and will ordinarily have no problems at low speed.

Quote from: Beefington1975 on September 20, 2022, 08:19:51 PM

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???

As Ted indicated, I stood don't feel there is any effects likely from this. They have more tolerance to raised oil level that this amount.

Wouldn't discount the air filter as suspect though. Any significant impairment with this will impact that mixture and not be readily evident from just looking at the filter. Definitely worth trying with it removed to at least give you a check on condition and flow impact to running. Easy and costs nothing too.

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.

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.

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.

Quote from: Sesman on September 19, 2022, 06:54:15 PM

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.

Anything that passes the petcock filter is fine for the carbs. Slow jets are known to become partially blocked when bike is not used for a long period of time. Good fuels like V-Power and Ultimate can help. An additive, a socalled fuel system cleaner, can also help as long as there's still some opening. To have a first impression of the condition of the slow jets, have the bike idle and turn the airscrews completely in and then three turns out to detect any change in RPM. This is done one after the other and wait a few seconds after you have turned the screw. RPM will not change much but if it doesn't change at all, it's an indication that that particular idle circuit is not functioning as it should. Then it's time to remove the slow jet for inspection. This can be done with the carbs remaining on the bike. Removal of the floatchambers will make all 4 accessible for removal and cleaning. Please report back when you intend to do this for added advice. Blocked or partially blocked slow jets is a common issue.