Two Stroke Motocross
Two Stroke Motocross Forum => Technical => Topic started by: Swimr2DaResQ on December 18, 2009, 11:08:05 PM
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Hey Fellas,
Just curious if anybody has or had a KX250 from '99-'02, and had some input and or advice on this bike.
I got the bike from a kid who was scared of it and did not know a thing about it. It's been a great bike so far with no major issues. I have added a FMF SST pipe and silencer (it came with a Gnarly pipe, now it is so much smoother and revs alot higher with more power up top), VForce 3 Reed system (best mod I've put on so far, much greater throttle response over stock!!!), NGK BR8EIX plug, I'm currently running Silkolene Racing 2T pre-mix in 91 octane gas with PJ1 Octane Plus at a ratio of 32:1, rebuilt Carb (Keihin Power Jet PWK38S Carburetor with K-TRIC?) with stock settings, other than needle in third from the top position, throttle response is quick and crisp throughout the powerband, plug looks good(slighty brown in color when checked after an all out run). I ride anywhere from Sealevel up to 2000ft, i estimate about 90 hours, + or - a few ,by word of mouth from the previous owner and the time i've put on the machine, it starts within two kicks, the compression always feels strong (but i don't have the tools to truly test that yet).
It runs good, but it feels a little weaker than before the Carb rebuild!!!
I don't have any really big issues with it, I'm just looking to fine tune it and get the most out of the whole bike. I figured I'd start with the motor before I mess with Suspension and Chassis!
Any advice and/or input would be greatly appreciated
Thanks, Chad
2T's a Smokin', 4T's a Jokin' !!!!
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Good bike.My first mod was always a twin air filter and boyesen dual stage reeds(glass).I usually end up dropping two sizes on the main and pilot with this set up but it's a very noticeable mod-power and economy both.
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I had a 99, it was a great bike, very reliable. I added a 11oz flywheel weight. It helped to reduce the wheel spin, and put the power to the ground.
Jetting can really change the power delivery. When jetting, do one change at a time. This way you will know exactly how the bike reacts to the change.
If you run it a little fat, it will give you a little more torque. I try dropping the clip one notch to see if you like the power delivery, then go up one (from the current settings) to see how the power delivery feels, while checking the plug...
Let us know how it works out.
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Thanks fellas, the needle position will be the first thing i mess with, it will be a few weeks before i can do it, but i will let you know how it goes.
One other little thing i found, my subframe cracked. I plan on welding it, but i also looked at getting an aluminum sub frame. Has anyone ever used or have any comments on them?
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Steel is perfect.Clean it,mig it,paint it and be done.Mine has an aluminum subframe but I'd prefer steel,especially after having to bend and tig it after my last crash.
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I have a 2000 KX 250 and its the coolest bike I've ever been on. I got KTM SX 250 2004 recently but it didnt come close to the hellraising powerband the KX has so I sold the KTM last month, just didnt come close, it had a bit more lower torque but at expense of fun in the higher revs.. didnt see the point cos it takes all the fun away!
I ride mine on the road in Central London - creates a stir everywhere I go - just need to find a riding buddy cos im only person with a true MX 2 stroke on the roads here :)
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Does anyone know if a 2003-05 kx 125 or 250 swingarm would fit a 2001 kx 250, are the dimesions the same? i know there is not much difference in the frame but the swingarm is different.
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Does anyone know if a 2003-05 kx 125 or 250 swingarm would fit a 2001 kx 250, are the dimesions the same? i know there is not much difference in the frame but the swingarm is different.
The swingarm can be made to fit, but it will require the '03-'05 axle and hub, as well as the caliper and caliper carrier. In '03 the axle increased in diameter to 25mm.
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Hey Fellas,
Just curious if anybody has or had a KX250 from '99-'02, and had some input and or advice on this bike.
I got the bike from a kid who was scared of it and did not know a thing about it. It's been a great bike so far with no major issues. I have added a FMF SST pipe and silencer (it came with a Gnarly pipe, now it is so much smoother and revs alot higher with more power up top), VForce 3 Reed system (best mod I've put on so far, much greater throttle response over stock!!!), NGK BR8EIX plug, I'm currently running Silkolene Racing 2T pre-mix in 91 octane gas with PJ1 Octane Plus at a ratio of 32:1, rebuilt Carb (Keihin Power Jet PWK38S Carburetor with K-TRIC?) with stock settings, other than needle in third from the top position, throttle response is quick and crisp throughout the powerband, plug looks good(slighty brown in color when checked after an all out run). I ride anywhere from Sealevel up to 2000ft, i estimate about 90 hours, + or - a few ,by word of mouth from the previous owner and the time i've put on the machine, it starts within two kicks, the compression always feels strong (but i don't have the tools to truly test that yet).
It runs good, but it feels a little weaker than before the Carb rebuild!!!
I don't have any really big issues with it, I'm just looking to fine tune it and get the most out of the whole bike. I figured I'd start with the motor before I mess with Suspension and Chassis!
Any advice and/or input would be greatly appreciated
Thanks, Chad
2T's a Smokin', 4T's a Jokin' !!!!
It honestly sounds to me like it's top-end time.
Not trying to bash your mods, but you would get better results from a Rad Valve in place of the V-Force. And you couldn't pay me to run an SST pipe.
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alright that is good info, it sounds like it isn't really worth changing the swingarm out for a newer one.
I've had good reults with the v-force system, far better than stock, but i haven't used a rad valve system yet.
the sst pipe, i actually like, i had a gnarly pipe on before, the sst is smoother and still pulls harder and alot further on top. I might try a pro cicuit next or an fmf factory fatty, not sure yet!
I def need to replace the seals and gaskets, my seals are leaking oil from the top of the head, and i plan on rebuilding the exhaust valve(kips system) too.
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alright that is good info, it sounds like it isn't really worth changing the swingarm out for a newer one.
Nope, there would be no advantage.
I've had good reults with the v-force system, far better than stock, but i haven't used a rad valve system yet.
The V-Force will produce some improvement in throttle response, but no significant boost in actual power production. The Rad Valve on the other hand will produce tangible gains in power production, provided you know how to jet. If you can't jet properly, there's no point to installing any mods anyway.
the sst pipe, i actually like, i had a gnarly pipe on before, the sst is smoother and still pulls harder and alot further on top. I might try a pro cicuit next or an fmf factory fatty, not sure yet!
My dislike of the SST is not performance related.
Originally written by Moto814
The FMF SST pipe is an amazing pipe.
Why is it amazing? Because in just about every case, it will work WORSE than the stock pipe that came on the bike.
The SST uses a restrictive reverse cone and pressure bleed to intensify the return wave and lower the initial flow out the stinger section of the pipe. What that in turn does is increase piston crown temperatures and make jetting difficult at best.
Now increased piston crown temperatures can be compensated for to some extent with richer jetting. But, by doing that you are defeating the purpose of the pipe, and negating any power gain you may have gotten from the pipe in the first place. Why are increased piston crown temperatures bad? Well, in some cases they are not. You see most bikes are jetted horribly rich from the factory, and raising the piston crown temps in this case will "fool" the engine into thinking it is jetted leaner than it is. Which will in some cases improve power. But in most cases, it will just cause slightly better throttle response and an increase in the spooge out the back of the pipe.
After all that you may be thinking: "well this doesn't sound so bad, why are they saying this pipe is no good?" Good question. Here's the answer. Because of the restrictive nature of the pressure bleed from the pipe, it does not evacuate as efficiently as it needs to. This combined with the piston crown temperature increase yeilds jetting that is too rich. So now you have a pipe that "fools" the engine into thinking it is leaner than it really is, but also makes it much richer than it was previously. Here in lies the second problem. It makes jetting a nightmare. If you jet it by feel, you will be jetting richer, and compounding the too rich condition even more, making the bike run like a slug. If you jet it leaner, you will be increasing piston crown temperatures even more resulting in an engine siezure. Catch-22 anyone?
If you are buying a pipe for your bike, get ANY other pipe. Or better yet, keep the stock pipe. The late model (1999-2005) KX250 pipes are pretty good stock, and provide a good low to mid powerband. If you want more over-rev, go with a Pro-Circuit Works or Platinum pipe. If you want more low end go with an FMF Gnarly, or Pro-Circuit Platinum2.
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Thanks for the info!
I found a 03 swingarm on ebay as well 99-02 swingarms. just thought I would check it out. I really like this bike, and was looking to lighten it up a bit, i thought the newer swingarm was lighter and stronger, but regardless it would'nt be worth the effort to change it out.
I am going to try the ATF fluid now as well, i really don't like paying 8 bucks a quart for racing oil every other ride!
Do you have any other suggestions about this bike and or performance?
Thanks again,
Chad
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thought the newer swingarm was lighter and stronger
It is, but not enough to be of any real significance.
Do you have any other suggestions about this bike and or performance?
Thanks again,
Chad
Give it a fresh top-end. You'll be surprised at the difference. The performance loss as the piston and rings wear is so gradual that you don't really notice it until you freshen up the engine and realize how much better it runs now. But peak performance starts to drop after as little as 10 hours.
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SST, mmmhhhhhh, Good to know!
Well, that certainly explains alot about the jetting issues I had, I think I will have to try another pipe!
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Does anyone know if the 03'-07' kx 250 plastics will fit the 99'-02' kx 250. I want to "pimp my ride," just a little face lift! 8)
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The easy answer is no, they won't fit.... :(
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Ok, thanks for the input!
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Does anyone know if the 03'-07' kx 250 plastics will fit the 99'-02' kx 250. I want to "pimp my ride," just a little face lift! 8)
The only part that will fit is the front fender, and even that won't match up with the '99-'02 number plate. Sorry, the plastics can't be made to interchange, they are just too different. The '03 and up uses the rear fender and side panels to make part of the air box, the tank is very different so the shrouds won't fit, and the tank won't fit the older frame. It just won't work.
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I think I will have to try another pipe!
Only if you are unhappy with your current setup. In my opinion, there is nothing wrong with the FMF SST pipe as long as you use the recommended silencer - SST or Titanium 2. I have used just about every pipe and silencer combination made over the years and the SST compares favorably with the best of them.
I don't mean to rain on anyone's parade, but you have to remember, opinions are like belly buttons, everybody has one. When you get information from the internet, treat it as just another source (especially when it's anonymous) and combine that with what you here from your riding buddies, the local pro, etc., and most importantly, what you can see and tell from the "seat of your pants". Then try to make an "informed" decision.
Here is a link to a website with some other riders opinions on the SST:
http://www.thumpertalk.com/forum/showthread.php?t=565192 (http://www.thumpertalk.com/forum/showthread.php?t=565192)
And as if that wasn't enough ;D, here are some more opinions for you. Don't use ATF in your transmission. ATF is designed for automotive automatic transmissions that have extemely small passages. As a result, it doesn't provide the surface adhesion and as a result, the cushoining needed for your application. ATF was widely used back in the day because a racer had a choice of ATF or petroleum based automotive motor oil. The ATF was the least offensive of the two. For proof, try this test. Pour a little ATF in your hand and move it around with your fingers. Now pour a little quality tranny oil (Redline, Maxima, etc.) and do the same. Notice a difference? That extra "heft" is very important for the care and well being of your transmission.
Finally, the VForce 3 reed is as good as it gets. I have run both the Boyesen and the Moto Tassinari on numerous engine builds. Both provide nice gains. The Rad Valve is easier to install (no modifications required since it includes the intake manifold) but cost much more. The VForce requires modifications on some applications but cost less. It all boils down to which one YOU like the best.
That KX is a great bike with an awesome engine. That PWKS carb is still state of the art, I run them on my racing CRs. Sounds like you are doing everything right. If the bike is starting to feel a little weaker, try a compression test. If you get less than 165, it's getting time for a new top end. Like i said, you should ask around and try to verify everything I said before making a decision. After all, it's just another opinion.
Main thing is have fun and take good care of your Kawi, it's an iconic model like the '01 CR250 Honda or the '03 YZ250 Yamaha.
dogger
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And as if that wasn't enough Grin, here are some more opinions for you. Don't use ATF in your transmission. ATF is designed for automotive automatic transmissions that have extemely small passages. As a result, it doesn't provide the surface adhesion and as a result, the cushoining needed for your application. ATF was widely used back in the day because a racer had a choice of ATF or petroleum based automotive motor oil. The ATF was the least offensive of the two. For proof, try this test. Pour a little ATF in your hand and move it around with your fingers. Now pour a little quality tranny oil (Redline, Maxima, etc.) and do the same. Notice a difference? That extra "heft" is very important for the care and well being of your transmission.
Can't wait for some responses on that one. I'll just answer it with a question. Do you think the constant mesh gears in your bike are dealing with more force than say, a Ford F350 automatic transmission?
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And as if that wasn't enough Grin, here are some more opinions for you. Don't use ATF in your transmission. ATF is designed for automotive automatic transmissions that have extemely small passages. As a result, it doesn't provide the surface adhesion and as a result, the cushoining needed for your application. ATF was widely used back in the day because a racer had a choice of ATF or petroleum based automotive motor oil. The ATF was the least offensive of the two. For proof, try this test. Pour a little ATF in your hand and move it around with your fingers. Now pour a little quality tranny oil (Redline, Maxima, etc.) and do the same. Notice a difference? That extra "heft" is very important for the care and well being of your transmission.
Can't wait for some responses on that one. I'll just answer it with a question. Do you think the constant mesh gears in your bike are dealing with more force than say, a Ford F350 automatic transmission?
Excellent point, enough said.
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Can't wait for some responses on that one.
To all the other PEs out there, I welcome any informed rebuttal.
I don't want to waste my time generating a response so I'll let the good folks at AMSOIL list the perils of using ATF in a wet clutch motorcycle transmission:
"Viscosity is the most important characteristic of a lubricant. Motorcycle gears create a shearing effect that causes permanent oil viscosity loss. This thinning effect reduces the oil's ability to prevent metal-to-metal contact and wear. The stability and natural operating temperature ranges of the premium synthetic base stocks used to formulate AMSOIL Synthetic Motorcycle Oils eliminate shear and reduce wear. AMSOIL Synthetic Motorcycle Oils exhibit absolute shear stability as measured by the Kurt Orbon shear stability test."
AMSOIL Synthetic Universal Automatic Transmission Fluid (ATF) Kinematic Viscosity @ 40°C, cSt (ASTM D-445) 32.4
AMSOIL SAE 10W-40 Synthetic Motorcycle Oil (MCF) Kinematic Viscosity @ 40°C, cSt (ASTM D-445) 93.36.
High Shear Viscosity @ 150°C , 1.0 x 106 s-1 (ASTM D 4683), cP 4.52 (Kurt Orbon test)
I direct your attention to the 93.36 rating of the made for motorcycles MCF along with the respectable shear rating of 4.52 vs the 32.4 viscosity rating and no shear rating for the ATF.
In addition to the above good news about ATF, over the years, new and improved ATFs have been developed to meet the changing demands of newer ATs. For instance, type f and the newer type fa has more friction modifiers for Ford transmissions. Dexron was actually developed for a softer shift feel. The newer versions dexron III, merconV, Toyota type4, etc., were all developed for specific problems that arose from newer model transmissions (torque converter shudder,slow flow rate thru valve-body&solenoid packs,etc..). So, in a nutshell, you don't know what you are getting since nobody has ever conducted any performance or compatibility test on ATF in motorcycle transmissions.
At the risk of repeating myself, ATF is designed only to satisfy the performance designs/goals of a automatic automotive transmission, not the demands of a motorcycle gearbox.
One last "jewel" I'll leave you with. Some ATFs will swell/soften rubber components and others will shrink/harden them - watch out for those seals!
dogger
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Uh huh. I read that as "ATF is no good, buy our oil @ $10 a quart please." ;D
*edit*
The above is admittedly a lame response. I felt the need to elaborate.
Note that amsoil themselves do not apply a shear strength rating to THIER atf? I find that interesting. I don't think viscosity is as important here. Shear strength would be. No amount of oil manufacturer's jargon will change the fact that both automatic transmissions AND dirt bike transmissions use constant gear mesh. You can go 75,000 miles on an automatic transmission without service to the transmission fluid or filter. I find it hard to believe that a dirt bike can put more force on those gears than my 5,000lb truck does.
I'm no engineer, just an old shadetree mechanic. I've been running ATF in my 2 stroke trannies for nearly 20 years and have never had any transmission failure, nor have I ever replaced any transmission gears or components due to abnormal wear. That alone is evidence enough for me.
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I'm no engineer, just an old shadetree mechanic. I've been running ATF in my 2 stroke trannies for nearly 20 years and have never had any transmission failure, nor have I ever replaced any transmission gears or components due to abnormal wear. That alone is evidence enough for me.
I completely concur. I've been using it myself for over twenty years, and not only have their been no issues, I prefer the way it makes the clutch feel. And there's just way too much anecdotal evidence from thousands of riders that run ATF with no problems for me to believe it's unsuitable for our trannies. The simple truth for our trannies is that how often you change it is more important than what you put in it.
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The above is admittedly a lame response.
Those aren't the words I would use since the ATF and MCF I used for the comparison both cost $10/qt.
I'm no engineer
I am, and I certainly didn't intend to hijack this thread (sorry Swimr2DaResQ), to enter into a circular debate.
You are certainly entitled to your opinion just like you are free to run clam chowder in your transmission if
you like - I hear the Abu Dabu MX team has been using it for twenty years without a single failure.
I prefer the way it makes the clutch feel.
The simple truth for our trannies is that how often you change it is more important than what you put in it.
You are correct on both statements. If you feel compelled to run ATF, "it does improve clutch feel as long
as you know it is a change after every ride proposition." Eric Gorr
dogger
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Awesome, good debate!
I like to see this stuff on the forums and hear all the opinions.
I appreciate all the different points of view and the shared experience.
Thanks for all the info and input!
As far as the sst pipe is concerned, I love the powerband now, I will try other pipes in the near future, but the almighty $ is limiting that one right now. I plan on rebuilding the top end in a week or two, go Tax Return!!!
On a different note, has anyone used Moose Racing rims, or Excel, and how do they compare?
I have heard lots of negative things about Pro wheels and Warp 9.
Swimr
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always remember that a proper oil thread must degenerate into personal attacks. otherwise what's the point? :D
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always remember that a proper oil thread must degenerate into personal attacks. otherwise what's the point? :D
Said with tongue firmly planted in cheek! :P :P :P
This place is just "different".... I know I learn a lot and it's great to hear differing opinions w using experience and facts as it's known to each racer. After all there's more than one way to do everything in life...
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has anyone used Moose Racing rims, or Excel, and how do they compare?
I have extensive experience with Excels and Dirt Stars, both are very good. I have
friends who use Moose and they love them. The Moose rims run a little cheaper
than the other brands. Make sure you use quality spokes to add strength and
durablity. I have used, and can recommend Buchanan and Excel SS spokes. Be
aware that if you mix and match, you may have to drill the hubs or the rims to
fit.
The latest wheelset I built used OEM hubs, Buchanan SS spokes and nipples and
DID Dirt Star LT-X rims. I had to drill the spoke holes on the front rim to fit the
larger nipples and had to drill the rear hub to fit the larger spokes. The wheels
are super strong and about the same weight as stock.
Here is a picture of the completed front wheel
(http://i246.photobucket.com/albums/gg107/dogger315/1993%20Honda%20CR250%20Restoration/93frtwhl8.jpg)
I don't have any experience or know anyone that runs Warp 9 or Pro.
dogger
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Thanks Dogger,
I have ordered Buchanan SS Spokes( heard nothing but great things about them too), and Because of the Cash factor I'm going to try the moose rims and stick with my stock hubs, that are in really good shape!
I looked at the DID Dirt Star, Excel A60 and Takasago and I'd like to try them out sometime too.
Anyways, Thanks for the info,
Swimr ;)