I have been running my 1987 F2 with new Denso plugs for 5k kilometers. The bike was notoriously hard to start on cold since I bought it, little puff of black smoke at the red line aswell. Plugs had chocolate center and black outside so running a little rich.
Upon investigation I have found that previous owner fitted different fuel pump, hard to say what it is. Two straight 10mm fittings instead of curved ones as OEM. Plug looked untouched. I had another OEM working fuel pump which I installed and the bike is easy to cold start now. And felt more powerful and wot. My conclusion - too much fuel pressure causing carbs overflowing.
I did couple hundred kilometers and noticed significant hole between 4 and 6k which was not present before. I inspected the plugs and found out that front left cylinder is nice and chocolate all around while others are white.
Can I play with pilot screw first or just pull the carbs and recheck the float level? Mind you I had the carbs done by a shop right after I bought the bike. I check the carbs and they are synced properly, valves adjusted 2kkma before