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Hi there,

I'm hoping someone can give some advice...

I've noticed with my 65 Austin Mini 850 that idling speed tends to vary voluntarily. Often it will idle at different speeds from one stop to the next. Typically it idles pretty slowly with some spluttering and little puffs of black smoke but sounds fine when you put your foot down. Theres no smoke when on the highway at speed. Earlier this week the 3rd spark plug gave up which I noticed by removing its lead without any noticable difference in idling speed or sound. I decided to replace all the plugs. I noticed that they were all covered in black soot. This lead me to my Haynes which suggested a carb adjustment to the mixture. I hoped this would take care of the black smoke and black soot at the same time. Being somewhat of an inexperienced DIY mechanic and this being my first adjustment of this kind I pretty much followed the Haynes perfectly. However, after hours of adjustment and test drives I cannot even get it back to the way it was. Now if you rev the engine slightly it splutters and you can hear theres a problem with the mix. It now sounds horrible and drives like there are problems with the plugs again. So I removed the brand new plugs only to notice they were all covered in a thick layer of dry black soot. I wiped them off and put them back in and it sounds a little better. But I cannot for the life of me get the phucking thing back to the way it was! Should I just carry on fiddling with the jet adjusting nut and piston lifting pin or could there be other variables messing with me?

Any ideas or advice would be appreciated.

Did you check the valve clearances ? That should be you next port of call after the obvious plugs and leads.
Follow the haynes for this pretty, it's straight forward.

Smiffy is right, the key to setting an engine up is getting the mechanical stuff right first, tappets, valve timing & compression test, although valve timing is not an issue unless you've had the engine apart. Then progress to your ignition timing, get that spot-on, with a new set of points, a condenser & clean plugs, then you can tackle the carburettor, make sure your float valve is seating properly & that the float chamber vent is not blocked & the flexible pipe from the bottom of the float chamber to the main jet is clear. Check full & free movement of the piston in the dashpot, & ensure that the piston damper is filled with SAE30 (or I find 10/40 is fine) oil. Then adjust the mixture as described in the manual. That's the way I start to set up an engine initially, & it normally works fine. All the best of luck with that, I'm sure there is much more help available on here, if my suggestions fail.