Personally I think video how-tos can be great alone, but not in something like this due to the room for error by the video maker. Miss noting one vital step or give weak directions and it could be bad news. Too easy to make the mistake. They and pictures are great supplements to a well organized step-by-step or becoming extremely familiar with what is being done. I've not seen this video (don't need to), but it sounds like this video could cause a mistake if a step is not noticed or missed.

Marcelino did explain the KACR (as you clearly know, but for others' benefit). He said set in stock position on the cam (making it open 10 degrees earlier in the compression stroke after the mod) his engine fired up when cold, but apparently not easily, then was near impossible when hot. He pointed out the timing of the release bleeds off too much compression, opening too early and being open too long in the compression stroke, when attempting to start when the engine. He pointed out that the stock set up was right at the edge of too soon and too long and that he figured he actually dialed back the release a bit more than the roughly 10 degrees in his estimate, retaining more of the compression.

My difficulty in getting the ACR pressed out without risk of damage along with knowledge that some of the KLX650 members had disabled theirs (by grinding off the rivets) and how hard the 650 turns over even with the ACR, was why I disabled it rather than move it. The ease with which the 250's starter spins the engine, others saying they took off the springs, and the fact that neither the CRF nor WR had an ACR made me totally comfortable with pinning it disengaged. I am betting disengaging the ACR would make for better starting regardless of the situation. The ACR is just not necessary with electric start.

For those hard core who insist on and have installed a kick start. I have owned/enjoyed a few SR500 singles that use a manual kick start only. I can tell you a compression release is not an absolute necessity for a kick start either. On big singles with manual releases it is only used to ease over TDC compression to enable some crank momentum when kick starting, enabling the crank to spin through the next compression stroke or two and fire up. The automatic units make it easier and quicker in kick starting, but it can be done without any. You work the kick starter up to compression, then keep heavy pressure on the lever. The compression will bleed off letting the kick starter ease the crank just past TDC. At that point you just put a good hard boot to it, kicking all the way through, no ***** footing or you risk what could be a painful kick back. It is not something I did on a regular basis, but knew I could if needed - since I had tried it. The manual release just made the process faster to perform.

 

Kind of realized I never touched on this. Why in the world would one only do the exhaust only? Fact is that some only did the intake because the exhaust made starting hard to near impossible unless dealt with. I've explained how I dealt with it, quite easily.

So my answer is why would anyone change up the cam with the problematic KACR mechanism and ignore the intake cam, the simple one? That and (with the 2009 and later 250 specifically, I forget if it is a benefit with the pre-08s) why would anyone go against what was proven to function based on actual dyno run comparisons with a very complete, but a shade tough to understand, mechanical explanation of why and how. That would be like changing the jet needle in the stock KLX250 carburetor ignoring the pilot and main jets - why would anyone ignore the proven results of the whole approach and do only a portion?

Do them both. Other than shim valves if needed, don't change anything else except the cams to do an actual comparison for performance if you wish, but do both. Avoid multiple changes to avoid mixing results, jet before or after, but not at the same time - avoid confusion of cause and effect.

Sorry for the wordiness - nature of the beast.

 

"Marcelino did explain the KACR (as you clearly know, but for others' benefit). He said set in stock position on the cam (making it open 10 degrees earlier in the compression stroke after the mod) his engine fired up when cold, but apparently not easily, then was near impossible when hot. He pointed out the timing of the release bleeds off too much compression, opening too early and being open too long in the compression stroke, when attempting to start when the engine. He pointed out that the stock set up was right at the edge of too soon and too long and that he figured he actually dialed back the release a bit more than the roughly 10 degrees in his estimate, retaining more of the compression."

Changing the timing of either the cam or ARC can only change the timing of the exhaust valve opening and closing due to the ACR. It cannot increase the duration of the exhaust valve opening like you have described.....It can't open sooner and close later. When the exhaust valve closes (controlled by the ACR) on the compression stroke determines the dynamic compression.

Ride on
Brewster

 

Oh nice, like I said icing on the cake, if squeezing out every bit of power is important to you.

 

The ACR is opening the valve, not the actual exhaust cam lobe. I actually never said anything about duration, just that the valve is open too long, that the valve is cracked open too late or too soon allowing too much compression pressure to bleed off, making starting hard. My guess would be opening too late, allowing more of the compression pressure to blow out, but I don't know. Two fixes are re-time or disable, both keeping the compression a bit higher and apparently easier starting.

The most important point is the compression release on the 250 is about as useful as **** on a boar hog and can just be removed or disabled. It's a vestige of the kick start 250/300 that, based on other manufacturers' products and experience of many, should be deleted.

Since I honestly don't care if it is late or early, I'm not going to be too worried about which.

 

Matty, the jury is still out on that module. It has not been tested - before and after - on a motorcycle dyno. It has only been tested on an automotive dyno. The veracity of which has been questioned.