2006 F4i, ~9000 miles, front brake seems to not always be consistent in terms of how much I need to pull it in to get equal braking action, if I haven't used it in a while (15 minutes?) the lever gets a little bit soft, although it'll still brake hard enough to lock the front wheel. Bled the brakes at the caliper and also by ziptie'ing the lever overnight. Stock rubber lines, but the look to be in good shape, don't see any leaks in the system and it doesn't lose fluid.

I'm thinking either faulty master or warped rotor maybe?

Unrelated - if anyone has a yellow tailing fairing and/or a 06 yellow/gray left side fairing they're selling, shoot me a PM.

 

It could be the master cylinder spring needing replacement. Think warped rotors would mean brake judder?

 

Zip tieing the lever overnight? Sounds like a good way to not bleed them correctly...

 

Sounds like confidence in that front brake is missing and from your description I’d go for disc issue.
Time to give the brake a good overhaul and get you pulling stoppies, not stopping like your pulling up to the grid on your MotoGP bike.
Warped disc can be checked by lifting the front end and fixing a marker pen to your fork leg, just off the disc, and give the wheel a spin. The pen needs to be v close initially but if it’s out you’ll see it marked on the disc. Prove this by further spins after cleaning. There is a tolerance for “run out” but this is marginal and a true warp is clear. This method does work but be patient setting it up.
Get those calipers off and give the mechanisms a going over and clean them up. Force the pistons out and clean and double check everything. No point in putting it back together with any compromise anywhere. Check pad sliding pins for free movement ( an issue I’ve had ) .
If your brake lines all good, now time for good bleed.
Best of luck mate.

 

Makes an elegant gliding up to a stop rather difficult.....more like someone’s mate who’s borrowed it lol

 

Either the rotor is warped enough to push the pistons back in, requiring the pump to push them back into contact with the rotor, or your master cylinder is going bad.

 

wouldn't warped rotors cause a judder or even a twitch (feedback) into the lever from movement?
I would suggest getting some fresh brake fluid in the res. and doing a thorough bleeding with some clear tubing so you can be certain that the fluid is bubble free.