Had the same problem. Spent ah pong and ah crong trouble shooting till i found out i was loosing compression in a cylinder. Didn't bother to open up block, broken ring or sumtin. Engine was already rebuilt by previous owner almost a year ago so that wasnt an option and yd25 engine very expensive so ...
I have same set up on my RB / walbro with 10psi and stock everything else and got same problem when boost was raised. Problem went away when i gapped plugs to .8mm
