kx500 power opinions

[DoldGuy]

Tharden,
An article you might be interested in.

http://www.motorcycle-usa.com/276/1865/Motorcycle-Article/2009-Yamaha-YZ250-2-Stroke-Bike-Test.aspx

[Hillclimb#42]

 I don't know how anyone can say for sure. I hillclimb a 250 and the 500. Often, I am faster on the 250. I don't think the power is the same at all. The 500 clearly has more ponies at the wheel. Traction, ergonomics, suspension and of course rider skill, all play a part.  Even when I lay down a flawless ride on the 500, its not seconds faster, more like a tenth. Once your motor is running well, gearing is where its at. Optimum gearing choices change with every changing condition. Tire choice is another big factor. I would sell the flywheel weight to a tight woods rider, and ditch the reed spacer also, if you have one. I don't know about throwing a 15 on there, but I definately agree that the 500 can pull taller gearing than your buddies 250 will ever pull. I also agree that once you hit third, you should have all the speed you need to win, it would still be affected by your gearing choice as to when and how it got you to third.

[DoldGuy]

14/47 equals 3.357
14/48 equals 3.428
15/48 equals 3.2
14/44.8 equals 3.2

[Polar-Bus]

I don't know how anyone can say for sure. I hillclimb a 250 and the 500. Often, I am faster on the 250. I don't think the power is the same at all. The 500 clearly has more ponies at the wheel. Traction, ergonomics, suspension and of course rider skill, all play a part.  Even when I lay down a flawless ride on the 500, its not seconds faster, more like a tenth. Once your motor is running well, gearing is where its at. Optimum gearing choices change with every changing condition. Tire choice is another big factor. I would sell the flywheel weight to a tight woods rider, and ditch the reed spacer also, if you have one. I don't know about throwing a 15 on there, but I definately agree that the 500 can pull taller gearing than your buddies 250 will ever pull. I also agree that once you hit third, you should have all the speed you need to win, it would still be affected by your gearing choice as to when and how it got you to third.

Interesting post.
I'd be willing to bet you are "almost" as fast on a 250cc H/C for two reasons: 1) being chassis weight, i'll bet the KX500 has a good 20 lbs over your 250... (and 20 lbs that you are trying to drag almost verticle up a hill )   
2) "flickability", i'll also bet the 250 is way easier to keep charging straight up the nasty hill. KX500's are SO top heavy. Kinda like trying to get a bull to change directions quickly.... 

[tharden]

I have enjoyed reading the post and would like to know what kind of techniques are good to develop when drag racing the kx500.  I am always willing to learn and any knowledge that is offered is appreciated.

[azracer19]

I own a kx 500 with no mods ( to engine ) except gearing 15...44, I also own a KX 250 and 125. AS I dont race motocross on the 500 I am not sure about a 500 beating a 250 or even a 125 corner to corner on a track with lots of turns. I do know for a fact that the 250 and 125 will pull my 500 from the start somwhere between 2 and third gears the 500 catches up and walks away from them. The only bike I have owned  that came very close was a KTM 390. As far as the earlier comment about big nasty hills, which I have seen lots of, there is no other bike I would want then the 500 on a long nasty hill. just my opinion

[Polar-Bus]

I've had my KX500 out on the motocross track many times. It's NOT the KX500's strong point. A KX500 "drags" you around the track, rather then you driving the 500 around the track... however, talk about ROOST! Nobody ever follows directly behind me for some reason... LOL

[kaw rider]

Hillclimb
what year 250 do you have. I'll run some sims for you. It's all in the set up.

[Mick]

Are we still juggling the false presumption that more power = go faster in this debate???
Modern 250s are powerfull and incredibly fast, likewise a 500cc two stroke is even more powerfull.  BUT THEY ARE NOT FASTER!!!  Gernerally speaking...we can name niche applications all day 

We need to realize an engine's performance on the dyno is absolutely, postively, in no way shape or form an indication to how "FAST" the bike performs in real world.  Save of course for you guys thinking, "Well what about drags, the dunes, or hillclimbing?"  I got it, nothing beats a 500cc two smoke.  I'm talking about what the machine was specifically intended for.  Track and/or trail use.  Dodging trees, railing corners etc etc...

I wish 500s were as "fast" as some of you think they are 

My two 500s for example:
My KX makes more power everywhere than the CR, but the Honda is ALOT faster!
A modern 250 is as fast or faster than a 500 for the same reasons my Honda is faster than the Kawi.  They put more power to the ground, they build power quicker, they're lighter and whereas they may not produce as much peak power...they still produce rediculous quantities of it non the less.  It's quite simple.  Matter of fact my Honda, and I'm sure the KX500AF, feel like a 60hp 250 MXer.  Nothing at all IMO like the old steelies.  And when you ride a 500AF, you will know the difference between "POWERFULL" and "FAST".

A KX500 is powerfull.  A YZ250 is fast.  A 500AF is both powerfull AND fast 

[kaw rider]

Mick is right, you are compare old technology and new technology. Big differance.

250 new tech.
500 old tech.

[jfabmotorsports.com]

Hillclimb
what year 250 do you have. I'll run some sims for you. It's all in the set up.

Hey...Run a sim for me too, please....kx450f, 72 hp, modified to fire every stroke and runs on premix 

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[KXDINO]

Tharden

check the power valve arm  , exiting clutch cover, pull pv cover off.  Check and adjust shaft by loosening 10mm nut . my k5 is about middle of adjustment, it made a difference, I had no top end power. there is a hole in the shaft,  by loosening 10mm nut, poke a small allen key in hole , and adjust the shaft then tighten , do this then ride  if not happy try again , its a case of experimenting to suit you.

i found it best in the middle of adjustment.

my k5 blows off 250's and 450's in the sand up to fifth gear easliy, it will wheelstand in fourth gear in the soft sand .

let me know how you go

kxdino

[Polar-Bus]

my k5 blows off 250's and 450's in the sand up to fifth gear easliy, it will wheelstand in fourth gear in the soft sand .



kxdino

Pretty wild claim.

[KXDINO]

wild claims  you reckon

It's probably helps my k5 is in a kx 250  (01) frame for a start. different geometry helps

piston had window mod, fmf pipe/muffler off a AF500, v force reeds ,and a good sandcross tyre

if you still don't belive jump on the plane and come to australia and see  for yourself!!!!!


p.s your welcome to stay at my place so we can compare the 250's  and the 450's

[tharden]

I checked my power valve assembly and it is working fine.  It was very smooth and tight in action.  I went back to a 168 main jet and that seems to give it more grunt so I will try that on the long stretch.  I feel though my loss is in my riding skills.  I admit I am not the best rider which means I need more time out on the trails.  Which is a plus for me. Another thing, we did a compression test on the yz250 and it had a whopping 240 psi.  I could  not believe it.  That is 80 psi greater than my 500. But I do understand the 250 is compressing a smaller volume but..