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Discussion Starter · #1 ·
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It's been lowered front and rear, and lightened to 293 pounds curb weight including the rack.

The stock bars prevented lowering the front so I removed them, slid the fork tubes up, and mounted lightweight alloy racing clip on bars onto the tops of the fork tubes.

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By swapping the bar blamps left and right, the bars sit level for upright riding instead of sloping downward for the typical sportbike riding position. They m ake the bike quite narrow for easy lanesplitting in traffic.

I made up the shorty exhaust.

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Discussion Starter · #3 · (Edited)
Stripped off all of the smog equipment. Curb weight: 291 pounds. The engine looks a lot more uncluttered.

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The block off plate fits perfectly. It includes a neat electric plug with a resister built in to fool the trouble light. These parts are not available in the US, so I got them from Greece.
 

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Discussion Starter · #7 · (Edited)
Just installed CNC alloy shorty levers...

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Wow... what a difference! :)

The 3-finger hand perches are really thick and comfortable and not narrow like the stock levers. They are excellent quality, include all of the switch actuators, and they fit my 2021 KLX300SM perfectly.

Got them from ebay for $25 total.

Clutch Brake Levers KLX300

I highly recommend them... a really good mod at a reasonable price. :)
 

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Discussion Starter · #8 ·
I installed a KDX200 snorkel today. It has about twice the cross section area as the stock snorkel.

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So far there's no difference in just regular riding. It'll take a freeway run to see if there is any difference as the increased flow will only be felt at high rpms..
 

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Discussion Starter · #9 ·
I'm constantly experimenting with my SM so this is the latest one... extending the length of the midpipe into the muffler to produce more low rpm torque.

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I used an old scrap of pipe just to test the concept to see how it works.

Before adding the pipe, 6th gear was only useful when the engine was turning at least 4,000 (40 mph) or higher. Any lower than that and the engine would begin to lug. Now with the longer midpipe I can cruise at 3,500 (35mph) in 6th gear and the engine is perfectly smooth and doesn't lug one little bit.

So the test worked out great. :) Now I'll make a permanent part that fits better.
 

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2021 KLX300SM, 2021 XT250, 2002 XT225
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Just traded a kid a 2016 harley street with 5,000mi on it for a 2021 KLX300SM today. It's sitting at 1,400miles. Condition is mint. Ran it on a 45minute drive home today and it held up great on the highway. This is my first supermoto bike. I also have a 2021 XT250 and 2002 XT225 but they are set up as dual sports. I haven't found a whole lot online as far as mods go for this bike. From what I understand 2021 was the first year for the 300sm but they do have some limited parts in common with the klx250?

Anyway just wanted to say there is some good info on this page! Please continue to share any mods you carry out so we can use them! lol
 

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Discussion Starter · #11 ·
I installed an IMS 2.7 gallon gas tank. It fits nicely and installation was pretty straightforward. The stock gas tank had a tangle of three emissions hoses coming out the bottom, while the IMS has NONE. :) Just ONE pressurized line from the fuel pump in the tank to the fuel injector.

My KLX300SM averages 75 mpg, so the IMS gives me a range of 180 miles with a one quart reserve left over.
It also completes my project to black out the bike

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The little thingie on top is a vent valve. It allows air to enter the tank as gas is being used. It also allows air to slowly escape for heat expansion. And it also shuts off if the bike tips over to prevent fuel spills.

It's two pounds lighter than the stock steel tank, and holds 4 pounds of extra gas when full for a net weight increase of only 2 pounds. This is a small concession to make in order to get more travelling range.
 

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Discussion Starter · #12 ·
I've been continuing my exhaust experiments...
Because of the timing of reflected pulses, long exhausts tend to produce more torque at lower rpms than short ones. Evidence of this principle can be found in this new 2020 Akropovic Racing Line exhaust.

[IMG]

In order to get as long a pipe as possible to fit into the shortest space as possible on the bike, it has all sorts of crazy bends. It even attaches a chamber onto the headpipe to increase exhaust volume which has the same effect as a longer pipe. Here's another example of an Akrapovic Racing Line exhaust for a 2022 Yamaha YZ450. They actually put a corkscrew in the pipe to get maximum pipe length into as little a space as possible.

[IMG]



The stock KLX300SM exhaust pipe is 27 inches long. My aftermarket exhaust is 30 inches long so I extended the pipe another 10 inches into the muffler to make it 25% longer for a total length of 40 inches. The hole in it is for the O2 sensor.

I had been running a 5 inch pipe as a test of the concept, and this time I doubled the length plus drilling a more precisely sized hole for the O2 sensor for less turbulence.

[IMG]



[IMG]

I'm also running an FMF Megabomb header. It also has a similar chamber on it as the Akropovics for an even longer effective exhaust pipe length.

[IMG]

Just got everything together yesterday and took a short ride today. The engine runs really smooth and strong even down to 3,000 rpms. Oddly enough, the longer pipe actually made the muffler quieter. Go figure!
:lol3
 

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Discussion Starter · #14 ·
So do I. :)
It's lots of fun trying out ideas.
The next experiment when I get time will be removing the secondary throttle plate. Both the dual sport and the supermoto have that restriction, but NOT the offroad R model.

I believe it's responsible for that 7,000rpm "dip" in my dyno test results. Another guy hooked up a multimeter to the secondary throttle actuator and discovered that it stays half open until 7,000rpms and then slowly opens fully.

 

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Discussion Starter · #15 ·
I removed the secondary throttle plate.:)



Haven't gotten a chance to ride the bike much so far, bit I will and will report on the effect. I can say this, the bike picks up revs much faster when the throttle is blipped.
 

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Discussion Starter · #17 ·
I just did another mod today, that's related to the secondary throttle plate delete. I removed the spring on the ECU cam follower which acts on the primary throttle plate. this completely disconnects the primary throttle from ALL ecu inputs, and leaves the mechanical throttle cables as the ONLY input.

(with spring)
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(without spring)
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The follower is that curved arm with the round knob on it, and the ecu rotating cam is that elliptical shape which rotates to move the arm. The spring between them keeps the two in constant contact. So removing the spring isolates the primary throttle plate from any ECU controlled input making it solely mechanically operated by the hand throttle.
The ECU control on the Primary throttle holds the primary throttle plate open for a while even though the throttle has been completely closed. This creates a "soft close" whenever the throttle is released. It makes for slower shifting because the engine revs float and there is also less engine braking upon deceleration.
However, with both these mods the engine is much more responsive and requires less throttle input for the same rpms and engine load. I really like how the bike decelerates faster with more engine braking.
The ECU throttle disconnect also makes for faster more precise shifting as the engine rpms drop immediatly upon throttle close between changing gears.

It's like riding a different bike! 🙂
 

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1987 BMW K75c, 2022 KLX 300SM, Hawk 250cc Project
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[IMG]

New to the forum, really enjoyed reading your build process and well documented thread. Was wondering what diameter pipe you used to extend the 10" pipe on the inside? Do you get any engine lights for things such as O2 sensor, ECU throttle disconnected, smog delete or the secondary throttle plate delete? Thanks for taking the time to make this write up.
 

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Discussion Starter · #19 ·
[IMG]

New to the forum, really enjoyed reading your build process and well documented thread. Was wondering what diameter pipe you used to extend the 10" pipe on the inside? Do you get any engine lights for things such as O2 sensor, ECU throttle disconnected, smog delete or the secondary throttle plate delete? Thanks for taking the time to make this write up.
The pipe is just a scrap of 1 inch inside diameter electrical EMT.
I'm an electrician so I have LOTS of scraps. :D

I removed the O2 sensor,
ground one end of the tubing to a taper,
tapped it into the midpipe with a rubber mallot,
marked the tubing through the O2 sensor hole,
removed the pipe by gripping the end with a channelock and tapping it out,
drilled an oversized hole to clear the sensor,
tapped the pipe back in firmly with the mallot,
and reinstalled the sensor.
Even though the tubing is just a friction fit, it doesn't come loose.
I've ridden over 1,000 miles with it in and it's just fine.

No engine lights because the stock O2 sensor operates normally.

No engine lights from the smog delete
because it's just passive vapor recovery.

No engine lights from the PAIR valve delete
because it just injects air into the exhaust.

No engine lights from the secondary throttle delete
because the shaft still turns freely with nothing on it.

No engine lights from disconnecting the ecu primary throttle plate control
because the cam still rotates freely without being connected to the throttle plate by the spring.

I tell you, my engine runs SO good with these simple cheap mods. :)
 

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Discussion Starter · #20 · (Edited)
Because I'm a transportation road rider, I run between 3,000 to 5,000 rpms without lugging on a bike specifically modified to produce more low rpm torque.

These are the torque mods I did:

1. Tuneble Exhaust. Running three tuning plates produces the most low rpm torque.
2. FMF MegaBomb Header. The expansion chamber increases exhaust volume to produce the low rpm torque of a long header in the space of a short header.
3. Longer midpipe. I extended the midpipe 10 inches into the muffler making it 25% longer for more low rpm torque. Long Pipe = More Torque
4. Secondary throttle plate delete. Deleting the ECU controlled secondary throttle plate gets rid of that restrictive "dip" you see in the dyno chart above.
5. Primary throttle plate control delete. This disconnects the ECU from controlling the primary throttle plate making the throttle body solely operated by cable.
6. Delete PAIR valve.
7. Smog delete.


All of these mods working together make for a highly responsive engine without needing to "spool it up".
:-)
:)
 
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