Line Lock with Drum Brakes ?

Hey A Body racers. I have drums on all fours and took the car to the track for the first time this weekend. My line lock did not hold the car at all during the burn out. Foot braked at the starting line worked good. I'm hoping it only needs a tighter adjustment on the front shoes to give the added holding power. Or possibly the proportioning valve need tweeking? Anyone else have this set up with good results ? Thanks.