Looking back at your two previous 'Help' requests (and comprehensive advice given) re. 'Sooty plug' from April this year when you mentioned that the bike and Brit bikes are new to you it seems you still have exactly the same carb issue. You had already stripped the carb without curing the problem. It seems that the bike has never run satisfactorily.Bondy1066 wrote: I found nothing untoward when I stripped the carb down. I am going to put it back together and have another play.
Have you looked at and followed the set-up/tuning guide in the AMAL link previously suggested? If you have and the correct spec'n jets, slide etc. are fitted it is unlikely that putting it back together as it was before (which you may have done incorrectly last time) and merely twiddling with the pilot screw ( 1 and 1/2 turns open is about right) will be the answer.
Have you forced aerosol carb cleaner or WD40 through the pilot drillings to verify that they are clear? (If not, for all the good twiddling with the pilot screw will do you may as well go down the shed and wave your willy out the window )