I think your rear brakes need to be adjusted outwards. You say sometimes you have a full pedal, and this could be because you pumped the shoes out to the drums if you were using the brake, but then if you stop using the brake the shoes spring inwards away from the drums, and next time you hit the brakes theres a big gap for the shoes to travel before they make contact. Adjust them out and they will always be right up against the drums.

I'd also try bleeding the brakes, as its easy and quick.

-Scerb

http://www.scerbfab.com/carb_faq.html