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You see those little holes in the bottom of the reservoirs, those are the C-ports. The pushrod that connects the pedal to the primary piston, has to be adjusted or chosen or made to work whichever, so that when the pedal returns to it's parked position, the ports are all open. This so the fluid can return, and so that as the pads wear, fresh fluid can find it's way down the line..... in compensation... for normal wear. Proving the ports are open is easy if the pistons are properly parked, but you need a helper.
First a warning;
brakefluid softens and wrinkles paint and it only takes a short time; so for this test you will have to cover everything within a 30inch or more radius to prevent expensive paint damage. Keep some Brakleener aerosol handy and plenty of absorbent towels. I will not be responsible for your paint getting damaged.
Ok, get a flashlight and pop the top off the M/C, then shine the light down on the ports. Have your helper very gently , V e r y gently and s l o w l y begin to push the pedal down. Be prepared to yell "STOP!" and stop means stop and do nothing else, just stop. Ok you should see the brakefluid roiling around in the bottom like water when it begins to boil. This will only happen for a split second as the piston seals pass by the ports. as soon as you have verified one reservoir, yell stop!. And then have your helper slowly return the pedal . Then repeat in the second reservoir. This will prove the ports are open and don't have broken drill bits stuck in them.
Now, if your helper is over zealous and pumps too fast, it is possible for him to make a little fountain in there, which, if it stays in the reservoir,is ok; if it stays in the reservoir.
But if you don't see roiling or fountains, then you will have to take a closer look as to why this is.
part II
This is a good opportunity to do a second test, but in your case will be of limited interpretation. So let me first explain how it would work in a properly functioning system.
In a properly functioning system; It is possible with two or three pumps to get a high hard pedal. With each pump you can send fluid down the line faster than it can return. If you are watching and then lift off the brake pedal, you will see a little fountain, as the fluid finally is allowed to return.
Now, if it should happen that this properly functioning system had air in the line, then your rapid-pumping would compress the air, and guess what happens when you allow the pedal to return opening the C-ports. Hyup, the little fountains become geysers shooting fluid up to the hood from where it can be reflected in multiple directions.
Now in your system we don't know if this geyser would be from compressed air, or from a mechanical issue, like bent or sticking or wrongly installed pads that are acting like big steel springs.
So, if you try this, figure out a way to prevent the geyser from ruining your paint. If you do this with the calipers removed and the pistons immobilized, and you get a geyser; then, this can only be from trapped air or freakishly soft hoses.. This is a great diagnostic tool.... cuz if you don't get a geyser, then you don't have compressed air!................. and so,IMO, the next move is to pursue the possibility of a mechanical issue .
