problem with burning avi to dvd

HELP

I am only able to burn 70 minutes of avi files to my DVD. my avi files are about 90 mins and 700mb, and dvd can hold 4.7GB.
i need to cut some about 20 minutes of footage to be able to burn. my burner encodes then burn.
i tried converting it into mpeg files but i still can burn only 70 minutes into a dvd.
Any useful solution to burn more minutes on DVD
Please help me