Try this
This is not technically a clutch modification but it does apparently help with the notchy shifting and accidental neutrals. This modification may help with the issues surrounding the "neutral" problems and "notchiness" on the 250Fs. This modification may help with the problem of accidentally finding neutral, and may improve the notchiness. Basically when you look at the ramps that you have to climb to shift from 1-2 and 2-1 its immediately obvious why its a notchy transmission. Basically neutral is just too damn big and easy to find. This is a death sentence on a motocross bike and a constant source of annoyance for tight trail riders.
The Part
The shift star wheel is located under the right side cover under the clutch. In order to remove it the clutch must come off. It costs about $35. The ONLY tricky thing to remember here is that its not a 2-stroke so there are a few o-rings and seals that connect the right side case to the engine. Without a correct reassembly you may not have full oil pressure. Also, almost forgot, what flops into each "slot" is a wheel held on the end of a spring loaded shaft. The "wheel" is almost the diameter of a dime. This assembly is called a shift detent mechanism.
Operating Theory
Note that there is a false neutral between 2-3, 3-4 and 4-5. All bikes have them because it is mechanically impossible for 2 gears to be engaged at once. If you get nothing else out of this remember that it is there. And remember that when you are doing a big 4th gear jump, especially when the gearsets are lightly loaded (ie; partial throttle) KEEP YOUR FOOT AWAY FROM THE SHIFTER. Because there is always that slight chance that you could unknowingly pull your tranny into one of these false neutrals, with just the weight of your boot, and execute a perfect forward somersault. Not fun. The tranny will work fine as long as you don't hambone it. That's why the false neutrals are located on "points" on the star wheel. It is meant to flop into one gear or the other. Do not interfere with this process when life and limb are at stake. If you still have doubts put your bike on a stand. Snick it into 3rd. Now rotate the back wheel back and forth as you ever so slowly pull the bike into 4th. At one point it will go into neutral. Now you know where you are: you are balanced on one of the "points" on the shifter star wheel.
Procedure
Here is the stock part with marks where is should be modified. I used a file to do it. Remember that the point here is to make the ramps on either side of neutral similar to the ramps for the other gears. You also want to reduce the size of neutral itself. But keep the 2 "points" as sharp as you can as you can so the shift detent wheel can't rest there.
Final notes and warnings:
Its an easily reversible modification as a replace part is relatively cheap.
Understand the process by shifting the bike when its apart. Its important to get the "feel" of things so you know how far you should proceed with the filing.
Neutral will become harder to find, of course. This is the goal you want.
There is a possibility that the shift detent can "balance" on the points between 1-2 or 2-1 after you are done filling. This could lead to some funny neutrals when the bike is idling by itself. I have had ZERO problems, in fact that's why I started filing in the first place. But be warned. I would not go revving the piss out of the engine (in neutral / clutch engaged) with your friend standing in front of the bike.
Two things we all get out of this (regardless as to whether you do the mod or not):
Watch the weight of your foot on the shifter when jumping.
Don't stand in front of a bike that is being revved to the moon with the clutch engaged. Neutral is a very, very relative thing. It can come and go at the worst possible moments!