that is a symptom of your dizzy start your advance curve at idle speed. usually this means weak dizzy spring(s). an idle too high can also make this happen. the shop should set the advance curve higher than idle speed. if you can, try lowering your idle and see what happens. if same situation still happens, well, you need stiffer spring(s).
if you can find it, try B310 radiator. i've had good experience with those, friends too. very mild A15 using B310 radiator no problem. Malaysia is hot all year round. very hot.