2006 XB12SS front brake lever gets soft

[NorCalXB12Ss]

Bled brake several times but always seems to go soft again...
Rebuild master?

Bike has about 12000 miles on it.

If I do the ziptye on front brake overnight it helps but go back after awhile...

Done the mightvac and traditional bleeding...

[ocgreenmachine]

Are there any large bends in the line where there is a high point that may have collected an air bubble?

[user_deleted]

the XB brake systems the simplest disc brake systems in the world. all nissin components. it goes like this:
1-if you CANNOT bleed the system wherein virtually all lever free-play is removed in conjunction with a firm consistent lever feel then you have either improper bleeding method OR a faulty master cylinder OR both.
2-if you CAN properly bleed the system so that the above is obtained....and 24 hours later the lever reverts to a spongy feel and excessive free play you have an air-leak somewhere in the system.
if #2 applies carefully check the entire brake system starting at the top and working down to the caliper. air can only enter the system thru either low reservoir fluid level, faulty cylinder plunger seals, line to cylinder banjo fitting, faulty line, line to caliper fitting, or faulty caliper piston seal. all will need to be checked.