Iīve been reading the first post so many times, I already lost count. I am taking my bike next month to my Kawi dealer to get this mod done (intake, exhaust and ACR), but I want to understand whatīs going on. Iīve done some search on the net about camshafts and [I think] things are making more sense now. You said:

Please, let me know if I understand this right:

The follwoing is just considering the intake for easy of understanding. The exhaust will be the opposite.

One of the things that I was really confused with, it was to rotate the sprocket to advance and/or retard the timing. It didnīt make sense to me because if you have a rod with a round piece attached to it, and you rotate that round piece to the right or left, itīs not gonna make any difference.
But now I see that by doing that, you are just offsetting the reference mark on the sprocket when moving the bolt from the IN hole to the EX hole. If you put the camshaft back in, without considering the next step, which is moving the sprocket 2 teeth in the chain, and aligning the mark on the sprocket where it was before you removed the camshaft, your intake shaft will be advanced 2.5 teeth.
So, when you rotate the sprocket 2 teeths CCW and put it back in, youīll only have 0.5 teeth advance for the intake shaft.

Itīs like, give it 2.5 to the left and then take 2 to the right.

Please, Am I right? Did I get it?

Well, if I did, now itīs time to study the ACR mod.

 

Thats the way I understand it to work. Does anyone know how much power the webcams add? I would almost rather just spend the dough on those and not have to worry about modding the ACR.

 

Just when you think that the KLX is "figured out" somebody goes and makes a discovery. Thank you.

 

Automatic Compression Release (ACR) basics.

The ACR is located on the exhaust cam in order to position it near one of the exhaust valves. A ramp/tab on the ACR holds one of the exhaust valves open about 0.40" (10mm) for a portion of the compression stroke in order to bleed off some of the combustion chamber pressure, making it easier to kick the engine over. When the engine fires up, centrifugal force moves the ramp/tab away from the exhaust valve, allowing full compression. The 2002 and newer bikes come from Kawi with the ACR retimed near the "easy kick" position. If you retard the the exhaust cam on those, the ACR will hold the exhaust valve open higher on the compression stroke, bleeding off even more combustion chamber pressure which could lower the compression ratio enough to make it harder to get the engine to start. I'm sorry but I can't find my notes on the actual degrees before top dead center that the ACR allows the exhaust valve to close. I think it was around 45 degrees BTDC for the "easy kick" position.

Keep in mind that any changes in degrees of cam timing are doubled when measured at the crankshaft. For the ACR timing, a 10.5 degree retard change of the exhaust cam will result in a 21 degree change in crankshaft/piston position (BTDC).

Ride on
Brewster

 

Hey Brewster,

Thank you. That sure starts to clear things up.

So, we have to rotate the ACR so the exhaust valve won't open as much? Is this the reason why the engine won't start when hot? Not enough compression for a hot start?

 

"open as much"? The ACR keeps it open the same amount of degrees of rotation before and after the relocation. When the exhaust cam is retarded, the un-modded ACR is also retarded, opening and closing the exhaust valve later in the compression stroke.
I don't know why a hot engine would make a difference in starting.

Ride on
Brewster

 

It makes a BIG difference. Have you ever had a 4-stroke motocross bike? They have a hot start circuit in the carb, just to make them start when they're hot.

 

I agree with your statement but the original question had to do with why the later closing ACR would be harder to start a hot engine than one in the original position. One or more of the early posts mentioned that.

Ride on
Brewster

 

Sorry, I understood it wrong the first time. I thought rotating the ACR would change how much the valve opens. But it changes when the valve will open during compression. Right?

 

Yes, it changes when it opens the valve and more importantly, when it CLOSES it.

Ride on
Brewster