I am having brake pressure problems on a 1992 mazda miata with abs. I have bleed both the front and rear brakes but this has not increased the pressure. The rear brakes have good fluid flow when bleeding but the fronts only have a little coming out. Fluid will come out if I leave the valve open but very little comes out when the valve is opened with the pedal pressed. I bled the brakes with the engine off and the pedal had a little resistance. With the engine running, the pedal is much softer. I even bled the brakes with the engine runnig with no improvement. I feel that the master cylinder is probably bad. But I was unsure if the abs could have any thing to do with this. I would'nt think so but I am not an expert. Any suggestions? Thanks.

 

I would check/replace the proportioning valve to see if it's not working correctly. If you decide to replace it, now's a good time to get an adjustable one so you can set your own bias.
If I'm not mistaken, your car has drums in the rear which require a lot less pressure than do discs.