Skimmed through the thread so sorry if I've missed any points I had pretty much same problem on my old cbr125. White smoke billowing out and wouldn't start when cold. Took the head off and there was a slight split in the gasket and I could pretty much see where the coolant had dribbled in. Also getting bubbles into the radiator. Was sorted in a day at the cost of £210 but that was on a single cylinder 125! :lol: