SOHC.co.uk Forums > CB500/550
CB 500 K1 running issue
K2-K6:
As a test you can turn the air adjustment screw inward until they are 1/4 out from closed to see if it then runs rich (more like on choke) and assess if the idle circuits are flowing any fuel.
Just a way of seeing if there's any response there not to set them longer term.
K2-K6:
From original description, running on wider throttle and not lowered throttle openings, it does suggest there's some impairment of the idle fuelling circuit though.
If you can get them out in situ, it could be worthwhile checking the idle mixture jets to see if they are clear.
deltarider:
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.
Beefington1975:
--- Quote from: deltarider on September 19, 2022, 04:55:23 PM ---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.
--- End quote ---
Many thanks for the detailed advice. I shall try the air screw test. I have already cleaned out the pilot circuit on each carb (using a very handy guide elsewhere on this forum). This was making me hope it wasn't an ideal circuit issue - all channels were clear. I can't see how to remove the pilot jets with the carbs in situ so am hoping pulling the carbs again will be a last resort!
Beefington1975:
Thanks to all that have advised so far.
I've adjusted the air screws as suggested (to check the ideal circuit) and the revs change in the same manner as I adjust each cylinder. This indicates the ideal circuits are clear (?) - I admit to some wishful thinking here as, having pulled the carbs and cleaned them/checked for flow, I am loathe to pull them again so soon! Will do so if that's where the advice takes me though, of course.
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