WHAT DOES 4AGE 20V BLACKTOP FOR SALE MEAN?

I browse on the web that when they aren't nicely synced it might cause rich running, backfiring and vibrations. Possibly I'm contemplating the incorrect way but when they would not be synced then the fuel/air combination can be diverse wouldn't it?Which on is broader. I am just inquiring that for the reason that i have KP61 and i have only a block