So after reading up on and speaking to various members here, as well as doing my own research about the cam mod for this bike, Ive begun to research other ways of improving power and efficiency on the KLX.

I am intrigued in particular by all the hoops Kawasaki jumped through in order to get this machine to pass California emissions standards. This was obviously a very big deal to Kawasaki, and I'd venture to guess that California sales make up a significant portion of their total US numbers for this bike in particular, simply because of the type of bike it is.

We are all aware of, and a lot of us (at least non-CA riders) have taken the steps to remove, many of the restrictive emission controls. From the Kawaski service manual, they are as follows:

Its easy to see how the super-corked intake, lean jetting, and ultra-corked exhaust and cat converter rob power from this bike-- but there are other steps Kawie has taken to help with emissions, namely, ignition timing.

From sifting through the service manuals of the KLX, KLR, and KSF Mojaves, other than the valve timing, one thing that stands out is the lack of ignition advance on the 250s compared to all these other bikes. The US KLX ignition advances a max of 25 degrees BTDC on the compression stroke, compared to 35 degrees of advance on the KLR and Mojave models, as well as many non-US versions of the KLX 250s.

This is significant from both a power and emissions perspective-- it is well-documented that ignition advance less than 30 degrees @ ~3000rpm reduces HP and torque. So why would Kawasaki do this?? They do it because it is also well documented that less ignition advance ALSO reduces emissions of uncombusted hydrocarbons and NOx-- which is what they are more concerned with to pass CA emissions testing.

The bottom line is, you are never going to achieve the power and torque that this engine is capable of as long as you run the stock CDI-- EVEN IF you go with a big-bore mod-- the physics of ignition advance do not change much relative to size of bore and stroke-- they are more closely tied to engine speed. 25 degrees of ignition advance is far too late for optimum power efficiency on an engine that regularly pushes 6500rpm.

There are CDIs available, as pointed out to me recently by other members, that allow selection of 35 or 25 degree timing advance, and are also programmable should you feel the need to tweak further. This sounds like a great and worthy upgrade for the bike, but I have yet to read a real review of the differences it makes in the real world, let alone any dyno charts.

It would seem viable to me though, that a 35 degree ignition advance, along with uncorking, jetting and possibly the cam timing mod, would be your absolute best best for extracting the kind of power from the 250s that Kawasaki publishes for the AU and earlier models of the 250r and 300r.

 

The lack of knowledge concerning the effects of ignition curves on KLX250S power production will be "history" soon. We will have a robust data set concerning this issue in the near future. I have been working on this a while now and I suppose I should post the project.

 

I'll throw in my 2-cent observation/speculation on some of this concerning the KLX. The engine design...even though 4-valve, hemi-chamber, water-cooled...came right at the cusp of true emissions vs. power knowledge, and the issue of computer control with fuel injection. Additionally, you can't balance higher power numbers and emissions with a carb. While there are extreme exceptions, it takes fuel injection and an engine design almost from the ground up as a computer controlled, fuel injection engine to achieve really good power with passable emission control in the modern era.

Putting aside any need to meet emissions, ignition timing is almost always a beneficial way to add power and performance. However, in a carbed engine you better stay on top of carb tuning/jetting, or you'll burn a hole in a single-cylinder engine piston faster than you can imagine. I'm no engineer, but I've had my share of high performance automotive and motorcycle engines from mild to wild. Everything's a compromise, and with the good often comes some bad. Let's face it...basically our KLX is an older design. It's an understressed, overbuilt engine for the most part, but with that comes some extremely good reliability and durability. Modern engines have gotten closer and closer to offering high performance with total durability.

Back to the ignition advance, computer control is what really allows an engine to detect detonation and control the ignition advancing and retarding to an extreme degree to produce power, provide fuel economy, and prevent engine damage. This is a harder balancing act with the KLX IMO.

 

The KLX engine is really no different from any other carbureted 4 stroke, 4 valve, DOHC, water cooled engine from the 70s, 80s, and 90s.

If you are concerned about balancing power and exhaust emissions, yes, you have a problem (well, actually you dont, Kawasaki has solved it for you already ). If you want to improve power and torque however, there is nothing to be afraid of and absolutely no chance of smoking your engine using angles of at least up to -35 deg because we have the precedent of Kawasaki itself using (and publishing) that angle for its Australian model and the similarly designed KLR and Mojave engines. Even taken to the extreme of it, if you look at the timing of the KLR 600, you see the factory set advance of 40 deg. BTDC!



Now granted, the 600 has much less in common with the KLX than either the KLR 250 or the Mojave, but 40 deg advance is certainly not out of the norm for well established 4 stroke timing angles-- in fact, the range of 30 to 41 is usually where the most efficiency (read power) is produced. The ONLY explanation for the 25 deg angle on the US KLX is to help meet emissions standards, thats it.

Again, back to emissions-- we really need to forget about them/trying to balance them. I say this not because I dont care about the environment, but because any tampering AT ALL with the emission control systems, which include the stock ignition timing, is illegal, period (at least in CA it is). If we're going down that rabbit hole, theres no turning back.

In all, if the community can get together and produce some data on this, it would be very helpful for those looking to at least get the power that the engine was originally designed for.

 

"Get the power out of this engine that it was originally designed for"???

I'll contend somewhat that Kawasaki never designed this engine to be a fire-breather. And look...I'm not trying to dissuade anyone from pursuing the joy of modding the ever living snot out of this bike. You're fairly recent here, so you don't know how much some of us have actually modded our KLX's. Most here know I've spent my share of time and money jacking with this bike to get it where I want it, so I'm not trying to spoil your fun. And I really enjoy my KLX and use it for some serious off roading where I have to have a plated bike...just got back from 2 and 1/2 weeks in southern Utah actually.

I agree with you about the emission crap on the bike, and I wasn't promoting keeping it...goodness knows mine is long gone...heck, I don't even have the stock carb, bore, exhaust, etc., etc. Still, from the many years that some of us have had our KLX's and all the mods that have been done by many, I wouldn't get too excited about trying to make this bike become some kind of ripper. It really is a very good bike, but it's engine design is never going to get close to a real performance machine without spending more money than it's worth. While it is a 4-valve, water-cooled engine, so is a KX250F...and they have little performance potential between them.

Klxster, you've probably played with and studied some of the dyno results a KLX both stock and modded have produced. What are the highest realistic power numbers you've seen at this point? I can't remember any of the numbers I've seen up to this point, but I don't think any of them were earth shattering. And I think most of you know I'm no KLX hater by any means.

 

Well, TNC, running stock ignition curve, my bike is currently showing 23.64 HP at the rear wheel. That is the most stockbore power I know of. ( RayCours' 23.89hp doesn't count as he was running a custom built EFI system.) There is no data on max potential with a stockbore ( webcams, TM36-68, larger valves, porting, etc ).

I have studied the power results from all 351's I can find info on. It becomes clear what you get with each add-on after the initial BB install. While max power from a fully modded 351 with cams, larger valves, and "porting" is sparse, it is appears to be 34-36hp - while a max 351 with just cams appears to be about 32hp.


So, for $2500 or so, you can probably have right near the same (36hp) at the rear wheel of a stock KX250F.

 

Yes, thats correct. The engine that is in the 250s made its debut in the Enduro d/s kick-start KLX250R back around '93/'94 and in the US was replaced by the dirt only 300R, then returned again in as the 250s in '06 with electric start.

The KLX250R was listed (by Kawie) in its service manual as a 30+hp bike (most likely at crank, and uncorked as used to be possible) and had the 35 degree timing advance @5000rpm. This is the power and the tuning the engine was designed for, but you already know this-- why the ??? Its not like I am expecting to turn this thing in to a KX250f, but you know that as well.

Our current 250s engine is listed by Kawie as having 15 hp, and I was almost embarrassed by the sound of it when I first got on it. It sounded like a toy, not much louder than an electric scooter...

 

There was a hash over of the Aussie black box versus the U.S. black box a couple years back.

If I remember right the conclusion was the real gains were nearly a wash, but I could be wrong. Not going to search for it because I'm not going to mess with the ignition stuff.

 

Custom CDI unit for KLX250S - KLX/KLR 125/140/250/300 - ThumperTalk