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hey guys, I have had some troubles with my carburetors the last couple of months. When ever I have been out and riding for more then lets say 15-20min. the spark plugs always turns sooty, like totally charcoal black, I have changed the main jet from a 200 to a 150, but the soot still occurs on the spark plugs on both cylinders, they are dry and totally black. I have tried with the needle bottomed out, but this only gives me around 5 more minuts or normal driving. I just feel like, no matter what I do, I just can't get my old k750 to run well again. Do I just have to buy a whole new sets of carbs, or is there anything I can do with my other 2 sets of carbs, to get this old lady up and running well again, or is it something completely different that I have overlooked? what I have tried until now, to fix the issue: - change the jet to a smaller size (the smallest i got) - cleaned the air filter. - no air filter - cleaned the carbs and jets. - installed new floats and float needle. - installed a gas filter. - tried new spark plugs. - changed the gas hose to the carbs. - tried changing the carbs for either of the 2 other Pairs I got, but I couldn't get it to run at all then. (useful info if needed) Bike: KMZ K750 1963 (sidevalve, 6v) installed at the moment: spark plugs: NGK BP7HS K-302 main jet: 150 idle jet: 04 ? needle hight: second from the top. mixture screw: 1.5 turns out. ---------------my other 2 pairs of carbs:--------------- PZ28D (28mm) (PL10 stamped on the front?) main jet: 92 needle hight: - slide hole 2 (top hole) - needle hole 2 ( second hole from the top) --------------------------------------------------- K-37 (24mm) main jet: 150 (no needle at the moment, just slide, I used the needle from the PZ28D)