You got a GOOD batch of F Brushes if they kept getting better.
I love me some F Brushes but the batches are SOO inconsistant it's hard to use this brush sometimes.
766's will get better each run.
You may even try a good F or 767 on the + and a 766 on the - if you need a lil more RPM.The 766 will literally make the OTHER brushes last longer due to the Graphite in the brush.
The Hole really does enough for me expecially with today's batteries.
I may loose a foot or so to a really HOT motor on the straight but EASILY make it up on the infield.
766's are a BAD BRUSH to alot of people because they NEVER understood how to break them in or took the time to find out.
Whats funny is even in offroad if you took the motor and broke it in for say 3 minutes.It would literally be the 3rd heat or even the MAIN before it came alive.Guys would run 1-2 heats,and pull them out because they thought they were junk.
I would take their brushes,clean them and install in my motor breaking them in for 3 minutes,skimming the comm and doing another 1-2 and have a nice brush for a few weekends.
Had 100 pair in my box but hey if your throwing something useable away HOOK ME UP.lol
Spring Combo in Sedan on that brush amazingly alot of times is just Red,Red.Red/Red is on a FAST FLOWING track.
If the track is a lil tight then try Purple +,Red -.
If the track is REALLY small and tight then try Purple,Purple.