hi canbo...
thats quite strange about your experience with fuel as ive been using castor 20% and the engine was/is very hit and miss..my friends fuel was as i say 30% but it was a synthetic fuel n not castor...well strictly speaking i already had a half to quarter of a tank of my fuel in it and he just filled it up with his synthetic 30% fuel and for this engine the results were very much more improved..

how many compression rings do you have on the head ?? i just use one as any more make it run worse..

i totally agree with you the carbs are just too crude/simple.. i was thinking myself to put a small os10. in it but i dont know the best way to get the pinion gear on the os10 as i dont really want to adapt the os10 engine really...