Smokey Exhaust

[Druid]

Hi, help me please,

I have a 1971 minor, 1098 cc.

It has been standing for some months without being started.

It was then put in for an MOT and failed due to 'excessive smoke'

It runs well but smokes/black when ticking over and seems to get better when running. When you tick over the smoke is black with a vengence.

I suspected the piston rings/valve guides so did a compression test on the engine.

The test dry was virtually the same for all four cylinders 120 psi

The test wet was also the same for all cylinders 150 psi

Before I start taking the wrong bits apart has anyone any idea what the problem is.

M any thanks,

Druid

[Willie]

The fact that the smoke is BLACK suggests a very rich mixture,
so rich that it would make it difficult for the engine to tick over
at a normal ,slow, speed. Does your engine tick over at the
normal revs?? Obviously the increase in pressure on the 'wet'
test indicates wear in the bore/piston rings but if it was chronic
wear then you would be producing clouds of GREY smoke(burning
oil). Have you given the engine a good long run after its period
of standing idle?

[rayofleamington]

Willie is right as always.
It's hard to give a verbal definition for the colour but oil smoke is grey, sometimes with a blueish hue.
Petrol smoke is more black.
Standing for a few months is rarely a big problem, but to get a noticeable change on smoke is rare (normally it is stuck brakes etc..)
If all the cylinders show a similar improvement when wet then I doubt that would be it. If something has happened (like gummed up rings) it is unlikely to happen on all 4 cylinders at the same time.

It has been standing for some months without being started.

How long is some months? If it is a very long time (nearly a year or longer) then also you may want to use some fresh petrol. Modern petrol will go off and that is not going to help any diagnosis.