My old Benford concrete mixer is great but it goes through spark plugs at a rapid rate. Runs fine, does a great job but when that plug has been killed off the mixer will not work with a full load. The plugs are always black and no amount of cleaning can bring them back to life. I’m not really concerned as the old mixer is one of my favourite tools and the plugs cost about a quid each. My interest is in why the plugs fail. There is no wear to the electrodes and even cleaning with a fine wire(unravelled paperclip) between the metal and insulator will not extend useful life.
Can anyone explain why the rich running kills these plugs so quickly and if there is any way to refurb them?
My old trials bikes used to do similar if the mixture was rich or the spark was weak. Once it misfired or ran rich the soot caused the spark to track down the insulator. A bit of wire just between the electrodes is worth a go or a plug file or strip of emery. (The worse thing to clean plugs with is a wire brush as it adds metallic tracks to what should be a ceramic insulator and makes it worse.) You can sometimes burn them clean in a blow torch flame or lighting them after dousing in lighter fluid or petrol(!) but otherwise keep replacing them or improve the spark or mixture. Does it have points which need adjusting or a failed condenser which will cause a weak spark. Is the air filter blocked?
The plugs are NGK BPMR7A ‘R’ rated hot plugs, so I am doing my best on that front.
I have tried thoroughly cleaning these plugs, so electrodes wet and dry paper and then card to clean and a fine wire to dig any soot out from the gap with the insulator.
This does not work which is confusing me and I am intrigued to know what has dregraded the plugs irretrievably.
A cement mixer really does prove the point conclusively as a weak plug will not spin the drum effectively with a full load.