What condition are the brake hoses in?
Are they in the stock arrangement?
Do you use the stock handlebars?
funny you should ask that as i was juts looking at that as a possible explanation. i have drag bars, and because of it the brake hose goes down from the MC, then rises slightly up, and back down towards the banjo bolt in the middle of the triple tree. is air collecting there perhaps?
That is likely the problem. (Making your problem self inflicted.) Air rises to the highest point in the system. With stock bars, that's the master cylinder relief hole.
If you have a ridge higher than the master, the bubble gets trapped there, as they can rise no further. And, you can't push the bubble fast enough to get it down to the caliper bleed fitting. Almost guaranteed spongy lever.
What you can do, is temporarily mount the master so that that relief hole is at the highest point of the brake system. Then when you slowly cycle the lever, the air should escape that tiny bleed hole. With your non-stock line routing, the brake system CANNOT self bleed, and never will until you change the physical arrangement of the brake line or raise the master to high point of the system.
Cheers,
