I just finished rebuilding an XK 140 engine with C head and standard carbs for that engine, not 2".
I was getting coming white smoke out the front side muffler meaning coming from the front carb. I pulled the plugs and wire brushed them, that’s it. Maybe just one was a little black and fuzzy but not oily. I ran it again and I have no smoke, zero. I can’t explain that. I didn’t change anything else. My breather tube is absolutely clear, no smoke so I don’t think I am burning oil. The engine has been run for about an hour so I would think the rings are starting to work in. Does anyone have any clues why this would occur?
I know on 6 and 8 cyl engine, you should break in a motor a certain way. That is 2,000 rpm’s for 20 mins. White smoke normally means coolant not oil. I would think clean plugs would only be a temporary fix. Vary the rpm’s and see what happens. Black and fuzzy would mean a too rich condition.
I think you’re thinking of flat tappet engines. The 2,000 RPM thing is done to condition the cam lobes regardless of the number of cylinders. We do indeed have 6 cylinder engines, so the rule applies. Roller cam engines are exempt from this requirement.