My bike is completely stock so its understandable, but i have looked at several dyno's on big bores, and d-trackers. They dont seem to make any power above 8000rpm? It tapers off dramatically above that towards redline?

Can anyone give me a technical explanation as to what in the design of the engine is causing such a steep fall in top end power? It seems even with the web cams people are not getting much top end?

Is it timing? Or does the head lack flow? Cams not agressive enough? Carb doesnt flow enough? Is the rotating assembly too heavy? Crank, rod, flywheel etc?

I have searched alot and read probably 20 hours worth of info and am still unclear what the hold back is.

 

Looking at the specs and comparing it to a yamaha wr250x, the blue has 4 valves, but the stroke is 53.6mm vs the klx250s has 61.2mm of stroke. I dont imagine that making the difference?

Other than that the yamaha has fuel injection and a slightly better compression ratio?

 

Based on some fact and some speculation, here's my guess. The WR250R engine is based on one cylinder off the Yamaha R1 sportbike engine...the '07 model, not the current R1. That design is a high revving engine for peak power. I dont' know why Yamaha went that way for what is basically a trail/DS bike, but the end result is still a very impressive engine.

The KLX was designed in the classic Kawasaki overbuilt, understessed mode for what it knew was to be a trail/DS bike. It's stroke and head design definitely indicate a lower rpm engine, and I think most of us can confirm that...once proper mods are done. I've ridden two friend's WR's...an R and an X...and they don't lug or produce power down low like the KLX when mods are considered. However, the Yamaha doesn't seem to run out of power on the top. One of those WR's had an aftermarket pipe, intake mod, and Power Commander FI. My 300 jugged 250S would pull the Yamaha at slow speeds and low rpm, but the Yamaha was stupid fast when rpm and/or speed was achieved. Now, I actually liked my KLX for real off roading better than the Yamaha, as I think the power was better suited...more tractable in rough terrain. However, I think I'd choose the WRX over the SF for a motord where on pavement and such the Yamaha would just kill on the street. I think that modded Yamaha I rode might be capable of hitting near 100mph the way it was geared and hit it in a decent hurry for a 250.

 

I have rode both and the yamaha was deffinately fast by a long shot, but i got the klx for about 1000$ cheaper than the yamaha...So im hoping after going through the paces it will make up the difference.

Im just wondering whats physically limiting the klx in the top of the hp curve... I know cams dictate alot of this, but it seems even after the web cams its not that great? Or does a 351cc kit and higher rpm cams cancel each other out?

 

The stock cams are too mild. I'm surprised it revs as well as it does with such short duration.

 

Mr. P, did you see this thread?https://www.kawasakiforums.com/forum...s-27971/page2/

 

I had read that today actually Also am thinking of going with the TM36 carb...ill revive that thread from the dead in a minute...