Hey just wona know where the air mixture screw on my carby should b set at coz i jus bought the bike n found the screw is wwound all the way in wot should i do

Most air mixture screws you never have to mess with. In your case, someone else decided to do this for you. First, if your bike is running rough, make sure you do a THOROUGH cleaning of the carbs so that when you DO set the air mixture screw, it will do its job correctly. The normal procedure for the air screw is to start with the screw a few turns out (counting exactly where you are starting from) For this particular bike, lets say 2 full revolutions. Now, with the bike running, (it should be able to run as long as the carbs are clean) screw the mixture screw out however many turns it takes until the motor stumbles a little. This can be hard to hear sometimes, so you may have to repeat this step. When it stumbles, record how many turns it took. So, for our example, 2 turns, plus you turned it out another 2 turns, making it "stumble" at 4 turns out. Now, reset the mixture screw to 2 turns out. Do the opposite and screw in now, making note of when it stumbles again. lets say it stumbled at 1 turn in. Now we know that the best possible solution is to put the air screw between 1 turn and 4 turns out, which means you should set it at 2.5 turns out (which is half way between 1 and 4 turns out). After all of that is done, you will want to double check the synchronization of your carbs to make sure they are all within spec of eachother. I hope this helps.

Bruno