I've only had my '12 for 2 months or so, but I can't leave well enough alone, so I've been tinkering around with the standard stuff. This weekend, I finally had the time and the confidence to do the MCM mod. Before starting it, I did my research and talked with KLxster about carb setup. I had all the parts I needed, so I was ready.

Before I did the mod, I had installed a KLX300 header and muffler, removed the end cap, and put a turn down on it. I had also installed a Twin Air filter and removed the lid, and was running a DJ128 jet (the largest I had). The bike ran fine, but it felt rich down low and lean up high. It required the choke to start even in 75 degree air. A day of riding on the street and the exhaust tip was fairly clean, but a day in the wood and it would be covered in soot. I also had some pretty fierce decel popping.

On to the mod. The carb part was easy. I moved up to a K152 main jet, a 40 pilot jet, needle on #1N with two washers on top, and turned the screw out 2X. That should have richened the idle a touch to help with the decel popping and cold starts, leaned me out in the middle of the RPM band, and offered plenty of fuel at WOT.

Then I tackled the MCM. Following the instructions from the forum, it went smoothly. I checked the valve clearances and did not need an adjustment, so I preferred to leave the cams in the bike. That means I had to disable the KACR rather than remove it. After some trial and error, I opted to remove the spring. Once I saw how it worked, it was obvious to me that any RPM would have the KACR in the "disengaged" position for the duration of the running period, so it's not as if the KACR is flopping around in there. Centripetal force keeps it disengaged as long as it's turning. With that tackled, the gear change was straight forward. I checked the timing against pictures and counted teeth a dozen times before buttoning it back up.

With the carb back on, I thought I'd see how it would start without choke. Without any priming. Without any warmth (60 degrees in the shop). It started before I had fully pressed the starter button in! Hot damn, this thing is easy to start now. And it idles at 1200rpm cold! Once running, the throttle response sounded quick and healthy. A test ride confirmed that all was working. There is definitely more pick up off idle, and acceleration is improved. It pulls a bit harder and then flattens out past 8k or so. It sounds louder, but it seems to be more from the muffler than the airbox. I had run w/o lid before, and the intake howl was deafening. It's still loud, but it sounds like the noise has moved rearward. Decel popping is almost nonexistent. A few burbles, but no shotgun sounds like before.

All in all, it seems like a no-brainer. It's a free mod, takes a couple hours, and has definitive positive results. Thanks to all of the resources on this site, I was able to sort through a bunch of wrong turns (that I've glossed over here) and had plenty of pictures to compare to.

Best advice:
1) Just yank the KACR spring. It's easy enough, and you can always put it back to stock if you ever wanted to (for reasons unbeknownst to me). It also makes this a 2 hour job, as you only have to pull the valve cover and swap the gears.
2) Listen to KLxster on carb setup. Dude knows his stuff and was super helpful.
3) Get a foot or two of 1/4" fuel line before you start so you can replace the tank to petcock to carb lines. My bike's only 5 years old, but those hoses were on the edge of either wearing through or splitting.
4) Take your time with the MCM. It's really easy if you take it slow and one step at a time.
5) Listen to NPR, preferably the Moth Radio Hour or Car Talk while you work. It does wonders for stress and the time flies by.

 

Another happy customer! I did the MCM with the stock exhaust, and it was very noticeable compared to stock cam timing. With the FMF and Powerbomb, even better! Can't wait for my k158 main jet. Then we will see what all the fuss is about :P

 

Not questioning your results, but with changes to the exhaust, the jetting, the intake and the MCM, how can you be sure that the gains can be attributed to one over the other?

 

The exhaust and intake had been done for 500 miles. I could have done the MCM with no jetting changes, but research told me that the MCM needed more fuel. A longer burn should require more fuel. So for me, it didn't make sense to do the MCM and not rejet at the same time.

This wasn't a scientific experiment for me. I read what the experienced folks had to say, studied their dyno charts, and made the changes. And it goes! And holy cow, does it start up with ease!

 

Still working up the nerve to do the MCM. So, you just removed the spring and didn't wire the KACR in place? I'm not second guessing the wisdom of this; I just want to clarify what you did. Any other opinions on not wiring or pressing the KACR off the cam?

 

I would not hesitate to press the damn thing out. It was only needed with kick start bikes and even then it can be worked around by a knowledgeable thumper rider.

The electric start has no problem spinning the engine in single digit fahrenheit temperatures so get rid of it. I started my bike in 8 degrees no problem. Take the time press it out, a bit less rotating mass for what it is worth. Next time I am in the cam cap it will be taken out of my exhaust cam.

As for the wiring disengaged. Just two less moving parts. They still flop when first starting and when shutting off when the engine is around 600-800 rpm. Nothing negative about locking the shoes in position from a mechanical point of view, only from an emotional point of view, because of what I used.

 

fzrcraig, no one should have to wonder or question the effects of "uncorking", MCM, carb setups, etc.. We have all the "dyno chart comparison threads" to show the exact power differences.


I removed my KACR with a long drift/punch and a small sledge hammer..

 

Wasn't questioning the results - even stated that. The title of the thread is "MY MCM Experience" and I am just asking whether it's the effect of the MCM that the OP is experiencing or is it something else.

 

I see. You are wondering about the individual effects of each change and how they fit into the (overall) end result..

I think, at this point in our knowledge, it is safe to say that the MCM will make the most change/improvement, below 7K, as a "stand alone" mod added to any good running KLX.

 

I was about to say the same thing, the OP did like 5 major changes at once.... kinda hard to call this an MCM experience thread... but glad it worked out for him