Black Fouled Plugs

[faiz_mur]

Hi Need advice
My cb500k
All this while was running ok
No issue plugs colour was good
But recently all the 4 plugs have black dry carbon black

I did check n replace ignition coil
Spark plugs caps and plugs
Did check ohm resistance using multimeter
Bike using CDI
Did do Static Timing to F mark
Did valve clearance and cam chain adjustment

Need advice if its due to main jet can it been suddenly ?
I mean all this while was good with same jet
Carb fuel level was good too

Thanks

[deltarider]

Anything under the seat that could hinder air intake? Has the engine been idling for a long time? What plugs do you run?

[Johnny4428]

Choke?

[Johnwebley]

Ideally you check the ignition timing with a strobe at +4.500rpm.



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[K2-K6]

Have you checked the air filter?

[philward]

I'd be inclined to check the previously mentioned air filter restriction (under seat inlet). For it to happen suddenly is unusual for an air filter to suddenly get clogged - but its pointing to that area as all 4 cylinders affected.
Only other common part to all 4 cylinder (although obviously timed differently) is CDI - I don't know anything about the workings of those but maybe another forum member could advise if the CDI could affect all 4 cyclinders at once

[hairygit]

I'd be inclined to check the previously mentioned air filter restriction (under seat inlet). For it to happen suddenly is unusual for an air filter to suddenly get clogged - but its pointing to that area as all 4 cylinders affected.
Only other common part to all 4 cylinder (although obviously timed differently) is CDI - I don't know anything about the workings of those but maybe another forum member could advise if the CDI could affect all 4 cyclinders at once

No SOHC four (except CB650) came with CDI, they had points and condensers. Highly unlikely to be an ignition related fault on all 4 cylinders. As previously suggested the sudden occurrence points to restricted air intake or sticking choke flaps.

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[taysidedragon]

I'd be inclined to check the previously mentioned air filter restriction (under seat inlet). For it to happen suddenly is unusual for an air filter to suddenly get clogged - but its pointing to that area as all 4 cylinders affected.
Only other common part to all 4 cylinder (although obviously timed differently) is CDI - I don't know anything about the workings of those but maybe another forum member could advise if the CDI could affect all 4 cyclinders at once

No SOHC four (except CB650) came with CDI, they had points and condensers. Highly unlikely to be an ignition related fault on all 4 cylinders. As previously suggested the sudden occurrence points to restricted air intake or sticking choke flaps.

This one has had one fitted previously.

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[faiz_mur]

Hi this bike using CDI which was installed by previous owner
It came with cdi black box aswell

I did timing check staticly havent try dynamic timing yet..
The bike doesn have air filter
Its just empty at the filter box area
but ya i did keep tools bag there
Might be chance  the make air restricted
I will try again..riding removing the tools bag
Thanks everyone

[faiz_mur]

Hi some update
I did adjust float height no 1 and 4 carbs because it overflow.
I did replace my rectifier

And ya did few mile ride and there was no more carbon
Im not sure yet whats actually caused
This
Thanks everyone