I've tried two new glowplugs with no effect. I've also richened the low end needle to the point that the throttle response is slow and bumpy. If i made it any more richer the throttle response would be too unreliable. I have tried a No.8 and an A3 OS glowplug in the engine. I'll remove the carb and flush it properly, before i try again.
Have you tried leaning the low end? A super rich low speed will cause the carb to load up quickly and kill the engine. Good rule of thumb is if one adjustment direction to the extreme doesn't help, go back to your original settings and try the other direction. Also, make sure you reset the high speed needle after every air bleed adjustment.
Brad