I am just wondering why an engines starts surging when it is acting lean. Why is it not just going flat, dies or blows to the moon and then quits.Why the up and down motion of the engine? And then an other thing. I am at WOT. I realise that my engine is flat at top. I expect it to be too lean. I am closing the throttle at it starts to surge. The surge occurs at closed throttle. Why, my lean condition is at WOT, not at idle. And then the last question. I start my bike with choke on, after it starts i rev it two times and then close the choke. Warm it up for a few more minutes and then start riding slowly. After that it is warmed up, say after ten minutes from the start it is acting lean at the pilot circuit(1/8 throttle). I dial in the airscrew to fix the problem. So far no problem. But the thing is that i do not really understand why the engine starts acting lean after 10 minutes, why not right away when it is still cold and so needs more fuel to compensate the condensation of the fuel against the cilinder etc. I would say that after it is warming up it needs lesser fuel in stead of more as it occurs. I know i am putting salt on the issue but maybe you guys can straighting things out for me.