So what's the difference if any between the jdm ecu and the unrestricted ecu that klxster is talking about? Do you have an ecu available for purchase? It would really be nice to see some numbers and dyno charts showing the difference between the options.

 

Unfortunately there is no direct comparison between BDSB and unrestricted JDM ECU. I would love to run them on the same dyno if someone will send me BDSB ECU. Other that that you can check my articles on planetklx2 https://planetklx2.netlify.app/docs/engine/ and planentklx2 youtube - https://www.youtube.com/@planetklx2.
I typically always have couple of ECU to sell, $350 - you can order on planetklx2 - https://planetklx2.netlify.app/docs/shop/.

 

I have one of the unrestricted JDM ECUs I didn't use for $300 if you want it message me.

 

I got my jdm 250 ecu from planetklx a month ago. It really makes the 250 what it should have been the whole time. You have to be ready to rev it but it runs so nice that way. I just did a few airbox changes to see if there was any gains knowing if i pull off the lid its going to be getting lean. it just made a lot of noise but I'm sure there is power there. I then went to the klx 300 cyl and cams. I got the 270 injector and the dolbec controller and tried to find a sweet spot. I could never find a perfect tune putting a 250 jdm or stock 250 ecu on a 300 setup. I always had some kind of off idle stumble. I only experimented with next to zero mods cause i like a quiet bike. the planetklx airbox lid didn't fit under the seat correctly and made too much noise for me but I knew it added power. I eventually picked up a 300 ecu and compared it to the jdm 250 ecu. The jdm still revs out a bit better, I can get almost 5 mph faster with it but it doesn't rev like the 250 cyl did (when i had the jdm on the 250 it was getting stronger as it reved even after 9k). I figured I could get about as fast with the 250 cyl and jdm in 5th gear vs 300 cyl jdm in 6th. (maybe the 250 can take full advantage of the head but the 300 cant??)


I realize this is all without a dyno and just an opinion but my position is get the jdm ecu for your 250 and leave it alone! or get the 300 with stp removed and kdx snorkel and tuner. If you need more than that consider the BDSB and other mods (they are deminishing returns IMO)

 

Cool, thanks for sharing your experience! I actually never tried JDM ecu on 250 to compare with standard 250 ECU. I upgraded to 300 just after several months after I bought the bike and I discovered "7500 rpm" limit already after that.
I have couple comments:
1. If you have problems fitting the snorkel - drop me a email at planetklx2@gmail.com - we will find solution.
2. Regarding intake noise. I hate noise as your do. Unfortunately opening intake makes it more noisy just because larger amounts of air enter the airbox at a higher speed. But the 7-10% power gain is hard to ignore. On 300 the noise increase over KDX was not substantial for me personally. But on 355 it became annoying. So I designed "baffle" for the internal snorkel inlet to make it quiter. Area-wise it match the outer inlet, so in theory power should not be affected. You can download and 3d print this "baffle" and try it - STL file link
3. Regarding 300 cylinder and how refined the engine feels. I suspect the issue could be with fuel controller (EJK?). Try to run just 270 injector + JDM ECU + planetklx2 snorkel. Fueling should be fine. My 300 with this setup (+ full exhaust + a bit more fuel) felt very very refined and smooth.

 

Thanks! I might try the airbox lid again. I did just what you said with multiple different mods and 270 injector vs dolbeck controller.. I'm real sensitive to right off idle and thats where my trouble always was. It seemed like if i added fuel as low as possible it got better but at different rpms the stumble would appear again. If I was doing mostly offroad I wouldn't be so **** about it and I would value the increased HP but I'm doing dual sport riding mostly so quiet and perfect throttle is my priority. Also my fuel mileage was about 10% down even with the o2 still plugged in so that seemed to me the ecu was getting confused or when i added more fuel (with the dolbeck) down low to get the stumble fixed it added too much fuel to the rest of the closed loop circuit? (guessing in the wind)

Thanks Planetklx2 for all your work on this bike!

 

one other thing, when I pulled my 7,000 mile 250 cyl/piston out and put an 800 mile 300 cyl/piston/cams,, I noticed how nice polished and new the 250 stuff looked.(looked better than the 300 cyl/piston i was putting in) I think the 300 vibrates a little more too. I really think the 250 with JDM ECU is a missing target that people should consider.

 

ECU's have multiple tables for driving a injector. In other words, a injector must be programmed into the ECU's "injector algorithm" so that it can be driven correctly.

From my perspective, slapping in some injector, without being able to configure the ECU to drive it, is likely to produce erratic behaviors. One variable alone - Scaling - must be set correctly for fueling to to ramp up and down (with RPM) properly.

I assume the pedestrian perspective is "bigger injector = more fuel".

Leaving the O2 sensor functional would be the only hope of getting the "lower performance envelope" ( closed loop ) fueling corrected.
But trying to use a piggy-back fueler to dump fuel into the closed loop operational envelope is, once again, incoherent behavior.

I'm just not aware of any "method" to this madness.

 

That fits my experience, Also when i used the stock 220 injector with the dolbeck controller, they have a product and setting for a 300 cyl upgrade. I had the same problem just off idle. I think they have an adjustment of when to start adding fuel (blue green IIRC) but that doesn't have an option to start at idle, just .5 so I couldn't add fuel low enough and again,, stumble off idle. If i added a lot to make up for the stumble the mileage got way out.

 

That "stumble" you are describing has all the characteristics of a air leak somewhere in the induction tract.