carbs out of sync issue I noticed

so my carbs are currently out of sync. I going to try to sync them closer with a home made manometer. but I noticed while trying to idle it's spitting fuel or air I think back into the carb. I think #1. I was told it could be a mixture problem. this wasn't happening before

Bench sync them then try again.
Steve

swest wrote: Bench sync them then try again.
Steve

how will that help?

I did a bench synch