This is a long and detailed post about a simple and
no-cost clutch improvement for the KLX250S/300/330.
The improvement is removing two of the six clutch
springs, which takes all of 10 minutes.

For more detail on that, plus additional information
on the effect of bike ergonomics on precise control,
please read on.

As a connoisseur of excellent clutches user of
high-level clutch techniques, the clutch on my`06
KLX250 turned 330 has been a disappointment. A bit
of a puzzle too because Japanese clutches are
usually excellent. Even with a well lubed cable,
the pull is on the hard side and the clutch tends to
drag past the release point. Combine those to
factors with another KLX trait: relatively low
flywheel mass (inertia) with a tendency to suddenly
stall, and you have problems with intricate
low-speed control that lowers confidence when things
get tough.

Intricate clutch work and precise throttle control
are critical to doing things like slamming into a
near-vertical 8-foot dirt bank then propelling
upward to land on top, with no forward progress, on
a 30-degree uphill slope of loose dirt. Rear tire
landing near the edge on top, still standing, I
start to creep forward after landing, with no loss
of traction. I use minimal throttle and ride the
clutch slipping it. That takes some deft throttle
and clutch work.

The mediocre clutch has made these sorts of things
harder and after a few hours, more tiring. Even if
you don’t use the clutch at this level, a better
clutch is something to appreciate. So I set about
fixing the problems.

I imagined all sorts of hours and experiments to
solve this one, and maybe some dollars too, but came
away with a laughably simple mod via reasonable
wrenching skills.

So what did I find wrong with the KLX clutch? Only
variable degraded overall performance. The net
clutch spring force is overkill… as in too high for
the application. Mechanical engineers don’t always
get it right. I know. I am one.

The clutch uses six conventional single-rate helical
compression springs. They have a free length of
1.386" and a wire diameter of .079". There are 5.5
active coils when compressed. That calculates to a
spring rate of k = 74.5 pounds per inch, assuming a
material shear modulus of 11.5E6 psi. Sorry, I
forgot to measure the spring length assembled
yesterday, but it's close to 0.80", which is 93
pounds per spring or 6 X 93 = 558 pounds net clutch
spring force. I found you can cut that by 33% and
get far better clutch action while avoiding slippage
when engaged under the most extreme clutch loading
tests I could come up with. To keep this shorter, I
won't detail those tests.

Procedure:

Clean the bike so you don’t get dirt buggers in the
engine. Don’t drain the motor oil. It stays at
rest below the clutch. Remove the clutch access
cover (six screws), then tap the cover with a
plastic mallet to shock the gasket free so the
gasket does not rip. The gasket should stay with
the primary cover. Pivot out the loose cover and
work out the clutch engagement mechanism from the
cover, without removing the cable. Set the cover
aside and rest the engagement mechanism/cable on the
primary cover out of the way.

Pull out the throw-out bearing and its round
machined aluminum housing as a unit and set it
aside. The stem has a washer where it contacts the
bearing. Don’t pull out the stem and lose the
washer! Remove four of the six 8mm hex screws on
the clutch spring thrust plate. Remove the last two
left on opposite sides, in stages, so the thrust
plate rises evenly under spring force until the
screws go slack. Remove the steel thrust plate.

Now you’ll see the six clutch springs. Lift out two
of the six springs on opposite sides and store them.
Reassemble the thrust plate using all six screws.
Before cinching it down, check the spacing between
the plate and the aluminum casting around to make
sure it's even so the throw-out bearing will run
closer to center. Replace the throw-out bearing
assembly.

Grease the gasket surface of the cover to aid
sealing. Work the engagement mechanism/cable back
into the cover and assemble the cover onto the
primary case by engaging the two dowel pins. Coat
all six case screw thread with grease so they can’t
corrode from trapped water.
Go ride, make ergonomics adjustments, and enjoy the
improvements.

Four springs isn't the only answer. You can try any
combination of springs that leaves the clutch force
balanced. Thankfully the KLX has six instead of
five springs, so you can try two (no need to), three
(works but slips), four (my recommendation), and
even 6 with a mix of say three stock and 3 softe
springs.

Replies about how the factory got it perfectly
right, how the clutch will slip, and that the bike
will spontaneously explode will be lost on me. If
you don’t feel comfortable doing this, then don’t do
it.

I can’t guarantee a 4-spring clutch won’t slip with
a KLX330 built to breath fire, but up to my 330cc
with stock cams and a re jetted stock carb and
KLX300 pipe, it works very well the clutch just does
not slip. If it does something else may be wrong.

Given this mod is so easy to do and undo,
experimentation is very low risk.

Bunus info:

Dry is bad, lubed is good. Lube the lever pivot,
cable end, and cable. Dry creaky cables fight
against the advantages of four springs in pull and
precision.

Bar and clutch lever ergonomics are critical to
precision use of the clutch, especially when
standing. Sub-optimal ergonomics are the rule, not
the exception. While everybody is slightly
different, and rider preference is a very complex
often cultural thing, being picky and analytical
about ergonomics can pay big dividends.

I’ve evolved through multiple competition venues to
disfavor the more typical ‘floppy-eared’ bar and
lever positioning of bars back and levers pointing
more down.

Unfortunately ‘floppy eared’ is assumed on stock
bikes, what with mirror mounts cast to support
angled-down levers on master cylinders, and plastic
nubbies in switch housings that lock into holes in
the bars. I have to grind off the nubbies (have to
with aftermarket bars anyway) and re angle mirrors
for my ergonomic preferences.

Though I am 6'2", I avoid tall bars or risers
because that can screw up handling. I get roominess
behind the bars by rotating the bars more forward
than typical. On my bike the grips tend to angle up
slightly when viewed from the front. That’s much
easier on my wrists, and I can stand without feeing
pushed back by bar grips low and back.

My levers are also not at a typical angle. They’re
a degree or so below level with the ground. I also
position the clutch and brake posts as far inward as
I can without the lever doglegs bottoming on the
switch or throttle housings. This gives my index
finger a little more leverage.

Now you may ask, “Aren’t angled-down levers easier
to get to when standing?” It’s contra-intuitive,
but not in my experience. It’s actually easier to
precisely control the clutch and brake levers with
one finger with more level levers. Sorry, that's
hard to describe. But What I'm after is one-finger
control sitting and standing with the second index
finger bone perpendicular to the ground when rocking
about engage-disengage on the clutch lever and
maximum braking force on the front brake lever.
This results in more lever slack than typical.
Running little slack makes the clutch action more
like a light switch.

The remaining fingers should be around the grip
relaxed, until a firm grip is needed.

I've been thinking of making some videos for YouTube
to illustrate this stuff. It’s more credible when you can see it in action.

I hope you all find this helpful.

 

Oh and I forget to mention that shifting gears when rolling slow and stopped is now much improved with the 4-spring mod. The reason is the reduction in clutch drag near the disengage range of the clutch when doing one-finger clutching, where the lever can't go farther than your other fingers.

 

seams like a good idea, i let you ride it for a few thousand miles first to see if theres any problems with it.

 

Wow, sounds like you are trying to do trials style riding with this thing! Good info though.

 

I'm sorry you are afraid, but the risk with this mod is near zero and limited mostly to lack of mechancial skills.

 

Among many other things, I do trials-like stuff, yes. But an excellent clutch helps in all styles of riding.

I see a long list of mods on your bike. When you going to try this one and report back?

 

Uneven pressure could maybe(?) cause distortion of clutch plates...
I'd be looking for softer springs that could keep an even pressure aeround the entire clutch discs (just my opinion).

Cool idea tho.

 

I'd kinda like to see the video of the:
"slamming into a
near-vertical 8-foot dirt bank then propelling
upward to land on top, with no forward progress, on
a 30-degree uphill slope of loose dirt. Rear tire
landing near the edge on top, still standing, I
start to creep forward after landing, with no loss
of traction."
On your klx250s,,

 

I did something like this last year; I was very jealous of the guy in front of me on a KTM 525 with a recluse clutch.

 

No... wire... hangers. What's wire hangers doing in this closet when I told you: no wire hangers EVER?...

...You've got any more? We're gonna see how many wire hangers you've got in your closet. Wire hangers, why? Why?