Just adding my 2c. As suggested, are the front calliper bleed screws facing up? Easy to get them the wrong way around and you won't get the air out of them.
Is to Vac line to the booster coming off the manifold or below the carb butterflies?
Try removing the line and sucking on it back to the booster. It should take up and hold vacuum.
Have you connected up the disc/ drum lines on the M/C the wrong way round. Easy to do as most M/C have to front outlet going to the rear brakes and the rear outlet going to the front discs. Check with your installation notes or Google it.
