Hello, I am at the end of my tether. Please help. I screw in 4 brand new Limbach spark plugs. The engine runs smoothly. After a while I detect vibrations, then check all the plugs and consistently one on cylinder 4 is black (all the others look fine). When I screw the sooty plug in on a different cylinder and run the engine, the plug will clean itself up (e.i. burn all the soot and look like new). Conversely, a clean plug mounted on cylinder 4 will foul up again. Has anyone had a similar situation? While checking the fuel mixture with Gunson colourtune https://www.youtube.com/watch?v=xEZ0-uN0NA4 , the mixture on cylinder 4 is slightly richer (e.i. slightly too rich) than on cylinder 2. How can that be when both cylinders are supplied by the same carburettor?
Looking forward to someone's suggestion Regards Jarek
