Amongst all the weighty deliberations on improving safety,
maybe someone experienced and knowlegable about diaphrgam carburetors
could give me guidance.
I fly a PIK 20E , Rotax 501 unreliable engine which has been behaving erratically, surging but not misfiring that I can detect.

From the plugs I see rear cyl lean, front cyl a bit rich.
Does a split carb diaphragm enrich or lean the mixture?

thanks

John F