1) Yes the mod is easily reversed for big bore. This mod is proven not to work as well on BB as stock bore.
2) The ACR is there for a reason. So yes have it retimed.
3) Show the tech working on the bike the thread and pictures to see if they will even attempt it. At least they will have the info and know what you are attempting to do.

Good luck.

 

I just did the cam mod on my new-ish '07. I'm not going to say it made a world of difference, but it definitely feels less anemic now. I made up a fixture to use on the press at work to move the ACR. Pressing it out and in was no problem, but how are you guys reinstalling it accurately? I got mine close enough, and it starts like a dream. But what if I wanted accuracy within a degree or two?

I have a question about the big bore. Why is everyone undoing the mod when installing a big bore piston? I understand that it doesn't make a difference with the larger displacements, but aren't the principles of cam timing the same? Since this mod seems to be correcting a factory error more than an actual modification, is there any issues or downsides with leaving the cams clocked when doing a big bore?

 

many saw a decrease in power with the cam mod on a big bore KLX.

Marcelino talks about it somewhere in this thread why he believes the performance decreases with the added displacement. I can't really recall, been a few years since I read through the whole thing.

 

Chinookmark, apparently, according to contributors on this thread, the mods works best on '09s and up. See #457, #435, #336

 

I will check out those posts, but it does make a perceptible difference on an 07. There is a hill across the street from my condo complex, and the bike cruises up in a higher gear now. Before I had to rev the engine a bit an wake the neighbors, but now I can putt up semi-quietly a low revs. Unfortunately, that's about as empirical a comparison I can make.

 

So is the lack of benefit on the earlier bikes because of the cam lobe shape, or because its timed closer to correct from the factory? I really need to make friends with someone with a dyno, because I'm curious now.

 

I think it's mostly because newer bikes have fuel injection and the exhaust sensors automatically the adjust the FI to match the new fuel requirements after the mod maximizing the hp gain

 

Well I finally took the ACR off and left it off.
First, thanks to all the people that did it and reported good results!
I will report this:
The cranking speed dosen't seem to have changed, it cranks freely.
In cold weather (38 F), with the bike stone cold and the "choke" on, and the starter jet drilled, it starts after cranking at most 3 revolutions. Almost instantly!
Hot starts fire immediately.
That clickly clackly idle and low speed noise is gone also.
I have over 29,000 miles on it now. I should have removed the ACR 25,000 miles ago when I put the B&B 300 kit on it.

 

In my opinion changing the lobe separation favors the efi bikes because the standard cam timing is effective beyond the efi rpm cutoff. On the carbed bikes (my 06 anyway) the cam mod fattened the midrange up bit but layed down on the top end. The carbed bikes will pull strong to a redline if jetted and uncorked, beyond that of the efi bikes limiter, so the stock cam timing is more optimal.

 

Hi

I have a fuel injected D-Tracker and did the mod about 6 months/10,000 kms ago. I couldn't be happier. Lots and lots more midrange punch with no apparent loss at the top end. Makes the bike a lot more fun. I removed the ACR and didn't put it back. My bike starts better! Makes sense too when you think about it. With the ACR compression is being reduced making the bike harder to start. Since I live in a warm climate there has been no issue about really cold mornings (but who rides then anyway?).

I wouldn't hesitate to do this again and I wouldn't install the ACR again either.

More fun for almost no money. What could be better.