Suzuki 2 Strokes

Hi,
I'm wondering if anyone else has come across this issue: I have restored, (on a tight budget I must add), a 1974 GT250L and a 1976 GT380A, both US imports. I replaced the front brake master cylinder seals and overhauled the calipers on both bikes. After bleeding, there is no free play in the lever, as soon as I move it, the brake starts to work. I can roll the bikes back and forth in a straight line, but turn the bars and the front brake binds, mainly if I go backwards.
The calipers release after hard lever pulling, so I don't think it's them causing the problem. I'm considering introducing a little air into the master cylinder, but I shouldnt need to bodge it like that.
Can anyone give me a little guidance please.

Did you make sure the tiny hole in the master cylinder is open? on the bottom of the master cylinder reservoir there are two holes, one larger that allows fluid into the plunger and one that releases pressure from brake line back into reservoir, it is very small and even hard to see, if this one is clogged the brakes wont release properly.

Thanks for the info Karl. I'll check for that.