Prior to adding Webcams, the power dropped dramatically after 8000 rpm. I noticed an immediate increase in usable revs after installing the cams. Now that the 331 kit is run in properly and I have tuned the EFI controller jetting, I am revving cleanly up to 10,000. The power pulls well up to 9000. So in my experience the Webcams have added an extra 1000 rpm of usable power up top. The extra 80 cc added the well needed bottom and midrange punch. ( Plus of course pipe, filter etc. )

 

I happened to open this tread about 20 pages back where it talked about having to undo the cam mod if you go to bigger bore-which I'd read already


I don't know why a bigger bore should require that. From what I've read or haven't read over many years displacement doesn't change cam timing requirements.

It's mostly about where you want the fat part of the power band isn't it?

 

In general, cam timing/profile requirements change substantially along with displacement changes (among many other variables). One size does not fit all.

 

I wasn't thinking of all necessarily.

More about how even changing just the bore size while the rest of the variables: stroke, ignition timing, intake and exhaust tract, gearing etc remain the same sees a reduction in benefit of the cam mod



Maybe as the bore increases in size the limitations of the intake ports/valves are revealed.


- IIRC there's been mentioned on forums that the KLX responds well to no air box boot at all. The total inlet tract length could be restrictive at higher rpm as the cc's increase



.

 

Richard, read page one where Marcelino talks about why it doesn't work on larger bores as well as it does on 250cc. I will try to expand on Marcelino's explanation. The larger the bore the more suction on the intake tract on every intake stroke. This will increase velocity of the A/F mixture through the tract and provides increased chamber filling, due to inertia, past the intake valve. This is more effective at lower RPM than it is at higher due to limitations on how much and how fast a given tract can flow an A/F mixture. Retime back to stock and you help cylinder filling at higher RPM - exactly where the tract needs all the help it can get. It's all about getting that broad bell curve of torque over as large an RPM spread as possible.

 

Thanks for pointing out. Reading on the first page I see Marcelino's mention that the original cam timimg of 110 deg was really for 'an' engine seeing 13,000 or more rpm-meaning our 250 would never be on the pipe bcz it doesn't rev as high as a Ducati etc

But then the author reverses his anti-110 deg stance because the bigger engine ahm doesn't seem to be drawing enough of the air needed as rpms climb so let's just put it back as it was and give up on it..

Maybe it's not getting rid of burnt gases well enough. Or other factors are at work.

Granted it wouldn't be easy to shorten the intake tract permanently. You could take the carb boot off and go for a drive...Or get serious and add a 40mm pumper after arranging the port and intake to let it bolt up and flow well, all with the cams in mod position.

Maybe there's something to be done instead of just undoing the cam mod. And maybe there isn't afterall

I'm trying be outguessing anyone mind you, I just think the original reasons for doing the mod are still valid, and the cam timing still needs to be optimized for with the rev limit of the engine in mind, and some other systems may have to be altered to let it all work together

Has anyone returned their bigger bore engine back to stock cam timing and seen a gain in power somewhere? I'll bet there are threads where someone has returned their cams to stock after adding a big bore...but I don't recall how well their bike ran afterwards

I have to catch up on all these mods and big bores as I have the 331 kit sitting on Bill's shelf, and my core arrived yesterday, so the kit will be winging its way to the Philippines soon-though it will take 3 months to get here

Maybe I can pull my cam cover off again soon and go ahead and do the cam mod so I know how the bike responds to it before I punch it out to 331cc

 

Can someone summarize this thread? I really don’t want to read through all the pages and it seems that there are conflicting answers to these questions.
Can I leave the ACR disconnected? Will the bike start ok if I do? IF not will just doing the intake make a difference? If it will how do I disable the ACR? Remove the spring?
Do I need to go up one size on the main jet?

 

Firstly, according to the thread, your 2009 will benefit fully from the mod. Older bikes apparently do not.

Yes, you can leave the ACR off the exhaust cam. Yes, you can deactivate the ACR by removing the spring. The starting system will see full compression. There are half a dozen or more posts stating that there are no issues caused by doing this. There are none claiming any kind of trouble caused by removed/deactivated ACR.

Yes you can do just the intake cam - makes the mod childsplay - and there are posts claiming it does increase power. There are no posts to the contrary. If you are capable of the exhaust cam and ACR re-position/deactivation and don't do it, you will always wonder how much more power you could of had.

Re-Jetting ? There is no answer other than put it on a dyno to get the A/F reading. My bike - as per dyno - needed stage II with the #132 jet - the #128 was still too lean for max power. ( I'm at sea level. See my mods below.) Feel free to pull up my threads,, there's charts,videos, etc. I'm running stock sprockets - your bike will have increased acceleration, due to the 13T, over mine.

 

Cmott, I did a little research for you.. I did not re-read the entire post..

For intake mod alone see # 94,114,121,122,162 . I stopped reading at that point.

Marcelinos' instructions for rejetting after cam mod is # 155 .

It is obvious to me that any fully de-restricted and cam modded KLX near sea level will need at least stage II installed as per instructions with the #132 main jet.

The loud intake grawl goes away completely with the mod, making running without the lid possible. Re-reading a little bit of the thread reminds me that more than a few fellas apparently didn't do the mod correctly. It's not a mod for the untalented.

 

Hi everyone,

I just did the cams mod 2 days ago, but I think something is not right.
I did notice a bit more power in the 6k-8k rpm range but my intake noise without the lead is still very high (much like the stock noise) and I think the bike is slower at low rpm.

Im gessing the exhaust cam mod is ok and that I missed a teeth in the intake cam, so now its half a teeth retarded instead of half a teeth advanced. Does that make sense?

Thanks