Topic: Blue smoke at low revs

[Lerby]

Hi i have a problem i hope you can help me with
I have a Honda CB 500 from 1976
i have just got it serviced, carb sync - timing adjusted and valves adjusted.
When i change gear blue smoke comes out of the exhaust,like a little cloud  but then its gone. its like i dosent fire on all 4 cylinders just after i have changed gear ( my theory)
and then if i idle the motor and then revs it, it smokes when the revs is going down again...
it dosent smoke when i drive at a steady speed, and if i drive like 40 km or so then there is no smoke

[dave500]

if you go down a fairly long decent throttle off for a while,then open it does it puff a little,valve guides and seals.in neutral holding it at say 2500-3500 steady look closely at the exhaust stream,little smoky?rings.if its got a lot of miles up it might be showing its age.

[Spanner 1]

Ride it, lots.... and then report problems!!...... will go away with Km's ridden IMO... Daag !! ( You might be Dutch).

[KingCustomCycles.com]

A splash of "no smoke" oil additive will stop the visual problem.  The engine is showing its age though.

[bryanj]

Is it a European 500K3, if so it has the emission re-circ via the air cleaner box in which is a foam filter below the paper one which can get oil logged and cause this problem

[Lerby]

i will look into this... thanks... is there a easy way to tell a K3 from a K2?

[dave500]

avoid any oil aditives as these will make the clutch slip.

[KingCustomCycles.com]

avoid any oil aditives as these will make the clutch slip.

Not all oil additives have the friction reducers that cause the problem.  I have used no smoke brand with success.

[Fritz]

I've got the same problem. Smokes when downshifting and idling. Smoke goes away with opening the throttle.

My head's got three exaust valve guides which are badly worn. As a result, the guide seals do not seal so well. When you close the throttle, the vacuum during the intake stroke will suck some oil through the worn valve guides into the combustion chamber.
Opening the throttle will reduce the pressure between the "cam side" of the head and the combustion chamber: Less oil leaking through the valve guides, less smoke.

To get rid of the problem, you either need a different head with good valve guides or have your guides replaced.

[bryanj]

Big differences k2 to k3
Year
Tank
Seat
Carbs

Post a picture and we might be able to ID it