D.I.Y Help (acapellas that go in and out)

i have a lot of tracks that i try to make into acapellas i usually use the invert/flip method
but with alot of songs (mostly with guitars or real instruments)
i get this problem
the music goes in and out into an acapella its very annoying is there any way i can help this (only other way i found is by cutting the instrumental up so it sounds right but that takes hours!)