Hi everyone,

Considering the injection timing on EFI models, I don't feel this mod is as "simple and foolproof" as it is for carbureted bikes. This might be an issue specific to the Japanese EFI model, but I'd like to hear your thoughts.
When I tested it myself, the mid-range power and acceleration were significantly improved. However, I experienced a very frustrating "hesitation" during re-acceleration around 4,000 RPM. I suspect this is because the valve timing was advanced, but the fuel injection timing remained delayed (at the stock setting).
In my opinion, to truly complete this mod on an EFI bike, you would need a full standalone ECU to adjust the injection timing. Otherwise, the synchronization is off.
Furthermore, I noticed a loss in top-end over-rev. My top speed dropped, struggling to even reach 110 km/h (approx. 68 mph).
Has anyone else tried the MCM mod on an EFI KLX250 without using a full ECU or fuel controller? I’d love to hear about your experiences and whether you encountered similar issues.

 

The MCM was originally developed on a Euro spec EFI KLX.

TBI systems ( like all KLX's use ) generally continuously spray without any specific "timing" . Those that do "timing" usually just pulse during the compression stroke.
So, I am having a hard time finding merit to the idea that MCM valve timing requires any EFI changes.

 

From what I can see regarding the MCM, it is just altering the valve timing.
I agree with Kkxster, altering the valve timing should not affect the fueling in any way.
Most EFI systems synchronize the pulse to occur during the intake stroke.

 

As noted by klxster, it was done by Marcelino on a European EFI model in the first place. It is simply narrowing the lobe separation angles (LSA), creating more overlap, which will noticeably boost power in the 3000 rpm range and up. It's a characteristic of any IC engine. What happens with a V-8 will be the same with the single.

Here's a video about LSA

.

 

FYI, TBI injection systems and Port injection systems are very different animals.

TBI's replace carbs and function like carbs.
Port injection positions an injector in the intake port - and pulses are precisely timed.

 

Thank you all for the great feedback. This has been very educational!
I’ve just learned about the TBI (Throttle Body Injection) system through this discussion. After doing some research, I realized that compared to PFI (Port Fuel Injection), TBI is a relatively simpler system and doesn't rely on such delicate, high-precision control. This explains why the injection timing might not be as critical as I initially thought.
I really appreciate the insights; I’ve learned a lot from this. Thank you again for all your help!