Hmm
First off... I'd make sure that you had deadlifts and squats in your routine (not your BICEP, but your back/leg)... perhaps bar rows as well. These exercises work ALOT of your body, and it gives you an overall pump that will help other muscles in your body to grow as well...
Secondly, I'd stay with the HEAVIER weights for arms... Perhaps trying a 5x5 plan... it seems to be working for me... 5 sets of weight that you can do around 5 reps of... then picking 2 other exercises and doing 2 sets on each with say a rep of 8-10... I found this has really helped me.
Third, during the week, everyday, get some bands (doesn't matter size) and do 3 sets of curls (loop the band under your foot) for around 25-30 reps or so... this will get blood pumping in yoru biceps and you'll get a "pump" from it... it should help your biceps in the growing process.
C-ditty