Morris Minor Owners Club

I had the same thing when I first got my Traveller. As said above (BMC etc) the cause can be a coked up cylinder head. I took the head off and cleaned everything and after that - no running on!

Redex did not cure it for my car. Before you remove the head- one thought- does your car have the correct spark plugs?

Yes its the correct plugs CJ, and they stay nice and clean too.
Bit reluctant to take the head off in the near future, can think of better things to buy than a head set for one, and to some stage want to get the whole engine out for a bit of mild Vizardry, so if i can hang on until then that would be best.

Bit of a light bulb above the head cartoon style moment, suppose the reason ive noticed it is that scabby is a daily used motor - whereas before i got it it would be out for an odd spin a couple of times a month.
Ive done a good few miles with what now know was incredibly badly set timing, guess thats just coked the head badly and now its quite apparent.

Will give it one good shot of redex in a gallon, maybe do one with the old acetone trick too although thats probably asking for trouble on the fuel pump diaphragm etc.
Suppose its worth a look in factors and see if theres some 'miracle' decoking bottle of whatnot. I did try the water in through the advance pipe too - might give that another shot, but rig up a pint bottle and take it for a good run rather than doing it sat still because that works - you could see the crud coming out as smoke in the exhaust.

Something else that can cause running on is air leaks- check your engine breathing set up for perished hoses etc.

This is likely to be a small hot spot in the cylinder head combustion chambers. Since it's running fine don't fix it.

1: Reduce tickpover speed to 550 RPM
2: Dip clutch as you turn off engine

from what CJ suggested i woudnt be surprised if the large breather pipe to the carb wasnt prime suspect now i think about it.
Remember one of the first jobs i did was eliminate the smell of petrol - there were 2 places, floatswitch gasket on the tank was fitted badly - and that large breather pipe.
Never replaced it but did have to shorten it, the end that fitted onto the carb was porous and oozing petrol.
Admittedly it was a 'Rountuit' job and nothing more than a quick fix, its sure not going to help, if that end of the pipe was degraded stands to reason the rest isnt up to much. Will replace with new when i get to the factors.
never know, fingers crossed, touch woood etc that could be the culprit?