CB 500 K1 running issue

[Beefington1975]

Hello all,

I've used some of the excellent advice here to help me get   my 500 k1 on the road. It was fine for a while, but has developed a running issue. I'm hoping for some thoughts/help on why it does what it does, please.

The bike will start, but will often cut out when pulling off. Then, after a short period of running it will fade at low speeds (making turns etc). The bike then won't start easily. And (strangely) seems more likely to start when on the side stand. When it does start again, only high revving will keep it going. I then have to nurse it back home, cutting out regularly trying to restart it.

So far, I have:
Cleaned and repaired the carbs
Fitted R9 fuel lines and fuel filters
Changed the spark plugs and caps
Adjusted the valve clearances
Synchronised the carbs
Checked the battery and charge (12.5v at idle, 13 5v at 4000 rpm). I did notice the voltage drop to 10v on start-up.
The bike has electronic ignition fitted- so no timing to adjust.

Can anyone offer some advice as to what to check next?

Many thanks

[McCabe-Thiele (Ted)]

Are you using the original coils ?

Are the leads still coming cleanly out the coils or has the outer lead started to separate worth a check.

[Bryanj]

What make of ignition?

[Beefington1975]

Are you using the original coils ?

Are the leads still coming cleanly out the coils or has the outer lead started to separate worth a check.

Thanks for the response.
The coils look to have been replaced by the previous owner fairly recently. The leads look clean and solid as they some out of the coils.

[Beefington1975]

What make of ignition?

Thanks for the response. It was from David Silver Spares - fitted by the previous owner in 2016

[Oddjob]

Fading at low speeds sounds like a fuel issue.

Have you checked the vac gauge adapter screws are secure and fitted with an alloy washer?

Have you checked the inlet manifold rubbers for cracks. I suspect an air leak somewhere, enough for it to overwhelm the mixture at low speeds and why high throttle openings still work, as it would on choke.

Also check the manifold clamps, possible a screw has failed allowing the clamp to become loose.

Try the carb cleaner trick, start the bike and spray carb cleaner around the inlet side and see if the revs increase, if they do, you have a leak.

[Beefington1975]

Fading at low speeds sounds like a fuel issue.

Have you checked the vac gauge adapter screws are secure and fitted with an alloy washer?

Have you checked the inlet manifold rubbers for cracks. I suspect an air leak somewhere, enough for it to overwhelm the mixture at low speeds and why high throttle openings still work, as it would on choke.

Also check the manifold clamps, possible a screw has failed allowing the clamp to become loose.

Try the carb cleaner trick, start the bike and spray carb cleaner around the inlet side and see if the revs increase, if they do, you have a leak.

Thanks for responding.
I thought fuel at first, so took the carbs off and on again, stripped and cleaned them and checked the rubbers and clamps - all look in good condition. Will try carb cleaner as you suggest.

[Beefington1975]

Fading at low speeds sounds like a fuel issue.

Have you checked the vac gauge adapter screws are secure and fitted with an alloy washer?

Have you checked the inlet manifold rubbers for cracks. I suspect an air leak somewhere, enough for it to overwhelm the mixture at low speeds and why high throttle openings still work, as it would on choke.

Also check the manifold clamps, possible a screw has failed allowing the clamp to become loose.

Try the carb cleaner trick, start the bike and spray carb cleaner around the inlet side and see if the revs increase, if they do, you have a leak.

Thanks for responding.
I thought fuel at first, so took the carbs off and on again, stripped and cleaned them and checked the rubbers and clamps - all look in good condition. Will try carb cleaner as you suggest.

Tried the carb cleaner trick - didn't change the idle speed.

[deltarider]

Inline fuel filters are a no no. Please read:
http://forums.sohc4.net/index.php/topic,190857.msg2220841.html#msg2220841

[Beefington1975]

Inline fuel filters are a no no. Please read:
http://forums.sohc4.net/index.php/topic,190857.msg2220841.html#msg2220841

Thank you. I'll take them off, but only added them after this issue developed in the hope it would help. I wondered if it sediment was blocking the idle circuits

[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]

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.

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.