Nigel, you are correct - KLX300R power is expected - and should be exceeded IF the butterfly delete+PCFC+Dyno tune is effective at removing the Kawasaki detune programming on the ECM. This should cost less than $500 to do - and if successful, would create a "lifetime" of rewards.

 

I'm actually quite happy with my 25 horsepower KLX.
It takes me wherever I want to go as fast as I want to get there. It's a perfect high reliability low maintenance daily utility transportation vehicle.

I love to tinker and am constantly experimenting mostly with exhausts because I'm interested in flow design. But I'm exploring a totally different direction from everyone else. My interest is in enhancing low rpm torque because I put in a lot of time crawling up and down steep narrow winding hilly roads loaded with tools and supplies. There is an interesting trend to longer exhausts with added "expansion" chambers on the headpipes. 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.



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. And has a chamber attached to 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 and added a chamber to get maximum pipe length into as little a space as possible.





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 tested the concept with a shorter 5 inch pipe,




and it worked pretty well so I made another extension twice as long with a way more precisely fitting hole for the O2 sensor so as not to be as disruptive to the flow. It's as long as it could be without hitting the end cap of the muffler.










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.



Just got everything put together late yesterday and will test ride it today. 🙂

 

The 40 inch long exhaust works great, especially between 3,000 and 4,000 rpms. Even short shifting, it pulls strong and smooth which is perfect for my uses. While I'm not exactly sure why, the longer internal pipe actually makes the muffler quieter, so I added another tuning disk to open it up a bit more while retaining the same sound level as before. I'm totally pleased with the results.

I did notice when I made the change, the bike ran ok but didn't feel much different, but after a few short trips it got better and better. This seems to indicate the ECU has some closed loop learning capability that takes a while to adjust to new changes in the operating parameters. I've only gone about 20 miles, so with more use I'll get a rough idea of how long the learning curve is. My Grom took about 50 to 60 miles to learn changes, so the KLX might be similar as they both have fuel injection with O2 sensor systems.

 

I FINALLY got around to removing the secondary throttle plate.


Haven't ridden it yet as it took a long time to dig down to the butterfly so was late in the day. But I'll be using the bike for work tomorrow so it'll get ridden a lot. I'll report on the effects.

I did have a chance to start it up, and the engine revs really rsponsively when the throttle is blipped.

 

Now we're getting somewhere..

Without any re-tuning of the fueling, your open loop ops up to 7500 RPM ( if I recall the stock power chart correctly) , are, no doubt, going to be extremely lean.. If I were you, I'd try to stay in closed loop ops until reprogramming of the fueling is accomplished ( PCFC and a dyno tune )..

 

That's no problem...
My klx is used daily as a utility transportation vehicle. With my low rpm torque mods, the operating range of the engine is 3,000-5,000 rpms. When I can find the free time, I'll likely dyno test again just to see if the secondary throttle plate removal takes that "dent" out of the results. I highly suspect that it does as the dent at 7,000 rpms PERFECTLY coincides with the secondary butterfly BEGINNING to open from 50% t0 100%.

I'm actually more interested in low rpm throttle response. It's telling that the dirt-only R model does NOT have it. And what you need MOST in the dirt is high torque low rpm throttle response for technical riding.

 

Does the EFI 250 have the 2ndary plate?

 

You can tell for yourself just by looking.






If you see that cam and elliptical wheel on the left of the primary throttle pulley, you got it.

 

Hate to say it, but I have to... When I read this thread title and owning a KLX250 I suddenly thought... it's like an unmuzzled chihuahua... a lot of yapping and nipping, but nothing like an unmuzzled big dog.

 

That's funny!

All my life I've ridden small underpowered 50cc to 400cc motorcycles for transportation, and the this is the latest in that long line of bikes stretching over 57 years. In my.opinion the KLX300 is flat out the best transportation bike I've ever ridden..

I just did another mod related to the last one. I removed the follower spring connecting the primary throttle plate to the rotating elliptical ECU actuating cam.

(with spring)



(without spring)



So now the primary throttle plate is solely controlled mechanically by throttle cable input and nothing else. The ECU controlled cam not only makes a fast cold idle which slowly decreases as the engine warms, it also holds the primary throttle open for a while when the throttle is fully released, making for a "soft close". this makes for slower shifting and less engine braking under deceleration.

I really like the increased engine control from BOTH the secondary throtle delete AND the ECU to primary throttle plate actuating cam. They work together to make a snappier more responsive engine with more engine braking and much faster shifting due to the engine revs dropping immediately upon throttle release between changing gears.

The engine still starts eagerly but without that "manic" high cold idle. It doesn't even want to die upon cold start because the a/f is still rich. It idles normally at 1,500 rpms just like when the engine is hot.