I just went thru a whole bottle of brake fluid trying the vacuum bleeder method, with the one from Harbor Freight. I could never get it to stop having bubbles appear at the bleeder valve... but... to be honest I'm pretty sure that's just air sucking in from where the tube is pushed onto the bleeder valve.
Remember... had same feeling of could never get it to feel tight and not spongy... installed caliper rebuild kit. Try again... got back again to same feeling of mildly taught but mostly spongy, where...again... you could squeeze the lever in until it touches the handlebar. Tore-down, cautiously cleaned inside master-cylinder being uber careful not to scratch inside that tube... installed master cylinder rebuild kit... God d**n it... back to only being able to get to a certain amount of tightness in the feel, still quite spongy, still can squeeze enough to have lever touch the handlebar.
NOTE: I have my KX500 right beside it so I can reference that one to know how the lever is supposed to feel.
ALSO NOTE: I DO NOT observe any leaking brake fluid! Not emanating from anywhere in the caliper area... not anywhere around the master cylinder. (There's a teensy bit of spillage at the bleeder valve from removing/placing the bleeder tube, but that's it... and I wiped that area dry before beginning procedure today with the vacuum bleeder.