It is absolutely important to "prime" the mastercylinder befor installation. I usually clamp it in the bench-vise, take a turkey-baster, yes you read right, fill the MC with brakefluid and activate it once with a large screwdriver. Hold it on the in-stroke, cover the outlets with your fingers so it will not suck air in when you let the scewdriver return. repeat that procedure untill brakefluid squirts out freely on every "push-stroke" Plug the outlets of the "filled" MC with the plastic plugs it comes with, while holding the screwdriver with your belly, you need both hands to plug the outlets. the idea is, that you have the MC full of fluid and not air when you are installing it.
After bolting the MC in place, fill the reservoir with fresh fluid, connect the lines, making sure the reservoir is toped-up ALL THE TIME. Yes, it is very messy so have plenty of rags ready to absorb the spilled fluid.
I have found that this procedure does not allow any air to get into the system and nine out of ten times you don't even have to bleed the system after.
Hope that this is of some help.....

CHEERS !
WITT !