Start by reading this. http://www.mikunipower.com/Manuals/VM_Manual.pdf
Most common problem is the smallest passages don't get cleaned, most newbs blissfully unaware they exist, where to look for them, cross drillings, etc. Not magic, simple physics (vacuum) and a bit of hardware.
Whenever cleaning a carb, you MUST verify flow in all passages... again for the back row, you MUST VERIFY FLOW in ALL PASSAGES! Use aerosol spray brake cleaner, and make sure it comes out AS EXPECTED!