Slight missing at idle.

[Moggie94]

Every few seconds at idle the car will miss slightly - then the revs will go straight back up to normal idle.
Goes away if I hold the revs high and never occurs while driving. - I can get it to do it at just above idle but it doesn't seem to occur any faster - same interval between misses.

It happens with the engine both hot and cold It's only slight, and it drives perfectly and gets regular performance and MPG.

Set checked mixture and timing - plugs are beige and it's just backed off from pinking under load
Checked all tappets -all are going up and down and set to correct gap.
Checked vac advance is working and not letting air in.
Last owner put a new rebuilt carb on it just before I got it.

Only just noticeable - but still very annoying sat at traffic lights. - being in the old banger sounding like it's gonna cut out.
I'm stumped, anybody else experienced this or any advice on what could be causing it?

[chesney]

Perhaps the idle speed is too low?
Is it just when it is warming up - first 5 miles or so?

[Moggie94]

If anything it's more when it's warmed up - on fast idle with the "choke" it doesn't do it.

[chesney]

As a temporary fix it could be worth just adjusting the idle screw by 1/4 turn or so.
Sure you'll get more answers soon ;)
Maybe just check the carb piston is freely moving, you never know..

[Moggie94]

I did check the piston was moving today - and maybe I shouldn't wait till 11pm before posting

[bmcecosse]

When you find out what it is - let me know please......mine does it too!

[Moggie94]

That's the impression I got from the Young Members group!

I have a sound clip of the "unacceptably" rough engine but don't think this forum allowed video attachments

[beero]

I thought all cars from that era did it. Are you comparing it to a newish car with injection and electronics?

[Moggie94]

I'm not expecting perfection of course it's a simple old thing, -but it's recently started doing it so it can't be normal.

[Windy Pig]

I have the same thing, and after going through all the obvious bits and pieces, and after speaking to a mechanic friend, have decided to leave it be. If you find anything though I would be very interested.

[Declan_Burns]

Mine also!
Regards
Declan

[kennatt]

and mine

[MarkyB]

My friends Morris does it as well!
I put a colour tune on it (quiet at the back Roy) and it turns out that the mixture goes rich just as it happens almost as if a drip of petrol had been introduced.
It could be the after effects of the miss but I seem to remember seeing the same thing on more than one cylinder.

[bmcecosse]

[Moggie94]

Messing with the mixture I can make it temporarily stop.

But it's a tiny range of adjustment that it needs to be within and will likely be thrown out by slight differences in conditions. -maybe this is what you'd need sensors and injection for, constantly adjusting themselves.

Mine's set to run smooth when warmed up now, it's still there but only just noticeable - it's better than it was, feeling the engine pulsing shaking the whole car.

[JOWETTJAVELIN]

Seems to be a common theme with the A-Series engine (especially transverse engined cars) that the idling can be quite rough. Irritating perhaps, but not a cause for concern.

[bmcecosse]

No - they are often silky smooth.......

[JOWETTJAVELIN]

Inline trans. engines are fine but for some reason every transverse B.L. car I've had seems to settle to a raucous chatter. Perhaps it's due to differing engine mounts and 1970's build quality, I don't know.

[bmcecosse]

Ahh - the primary gear can chatter if the end float is out of tolerance. But the engine itself can be silky smooth.

[Tom and Maria]

My engine has done this ever since I tapped the carb spacer for better fume extraction. My guess is that the mixture is slightly affected by the varying amount of fumes drawn off the rocker cover, although this wouldn't account for engines where the rocker breather goes to the air filter.

It solved the oil leak, so I am happy to live with it.

Tom