I have just purchased a series C Comet and having issues tuning it to run correctly. It came with a 930/71 Mk1 concentric carb, which was worn, so I replaced it with a new premium one from Burlen services. I used the same settings as the one that I took off but it ran very rich. Wet sooty plug and white smoke from exhaust. I've reduced the main jet from the 270 that was fitted to the previous one and gone down to a 250. I've replaced the throttle valve to one with a higher cutaway and moved the clip on the needle up to the top notch. None of this seems to have made a difference. The bike runs ok for short runs but the plug and clouds of white clearly indicate it's far from right. Anyone using the same carb and can let me know their settings or suggest other changes I can try. Many thanks.