Taming the beast, KX250

L

LWilson250

Member
Jan 1, 2001
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I am the proud new owner of a 1998 KX250. I just got the bike and right now it scares me to death. I had been riding an XR250R for 2 years before I got this bike and loved the smooth power but hated the suspension; weight and lack of “get up and go”. Now on my KX250 I have great suspension and very little weight but the power just scares me. The engine is completely stock besides the FMF Gnarly pipe. It has a fresh top and bottom end and a new clutch so the engine is in good shape.

My question is this: How can I tame the hit of my bike? I am thinking about getting a 13oz. Flywheel weight. For those of you who say it will be to slow well, slow is what I want. I need smooth manageable power. I ride mostly tight horse trails and will be racing hare scrambles so I need a 4-stroke like power with the 2-stroke weight.
Is there anything I can do with the porting to smooth the hit? I really don’t care if I lose some top end or RPM building ability. I just want a smoother more manageable bike.


Thank you,

Lee W.
 
C

crkid

~SPONSOR~
Oct 14, 2001
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the flywheel weight is probably the best idea for the time being, it's the cheapest and easiest to do. 13oz sounds like it will be a bit too heavy though, it might tame the power a bit too much. but what do i know.
 
L

LWilson250

Member
Jan 1, 2001
683
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I'm used to the really heavy flywheel on my old XR and my dads XR400 so I doubt it will bug me. Some of the trails I ride are tight enough to make it hard to get through on a bicycle so I need mellow power.

Lee W.
 
Vic

Vic

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May 5, 2000
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Lee, try retarding the timing. Turn the stator plate counter-clockwise so that the first mark on the plate lines up with the mark on the case. This works well on those bikes to tame the killer low-end hit. If that's not enough, the flywheel weight will also help or Eric can certainly port it for the type of power you want.
 
Vic

Vic

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I had another thought. If retarding the timing isn't enough, you could try running two base gaskets. The retarded timing and two base gaskets will also help over-rev, which that engine could use a little more of.
 
L

LWilson250

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Jan 1, 2001
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Thanks Vic, that's good info. I will try it. Also, do you think Eric could port my as to reduce the hit? I just want smooth low end. I would be happy to send the cylinder to him if he could fix my bike up!

Lee W.
 
Vic

Vic

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Originally posted by LWilson250
do you think Eric could port my as to reduce the hit?
Click to expand...

Definately, but I think you'll be pleasantly surprised at how just the timing change affects the engine. I had the same bike and didn't like the massive low-end hit either, but was happy after retarding the timing.
 
L

LWilson250

Member
Jan 1, 2001
683
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So what exactly will changing the timing do? What does it do to mellow out the hit? Before I start taking things appart I want to know more about it.

Thanks Vic!

Lee W.
 
T

troy2

Member
Oct 23, 1999
70
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L Wilson,
I may be of some help on this one.
I have a 2000 KX250, previous bike was a KDX 200. I know exactly what you are talking about.
First time got the KX in tight woods it scared the crap out of me. I was constantly stalling and restarting. First thing I did was get a 13oz. Steahly FWW. That is the heavest one they offer, if they would of had a heaver 1 I would have gotten that. BIG MISTAKE! It is too heavy and made the bike harder to ride because now there was a bog right off idle and then a major hit.
Second and best thing I did was talk to Eric Gorr. He ported my cylinder to work exactly the way I wanted. At the same time i installed a V Force reed cage. I removed the weight and love the power now. It is still a handful if soil conditions are not perfect so I talked to the guys at Steahly about getting a lighter weight. I sent my 13 ounce weight back and traded it for a 7 oz. Have not riden with this yet.
My rec. is to let E.G. port it and maybe the V Force. Wish I would have tried them seperately. If you go with this set up get back to me and I will help you with jetting.

Steve
 

Vic

***** freak.
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This is from Eric's website.

AFFECTS OF THE IGNITION TIMING

Here is how changes in the static ignition timing affects the power band of a Japanese dirt bike. Advancing the timing will make the power band hit harder in the mid range but fall flat on top end. Advancing the timing gives the flame front in the combustion chamber, adequate time to travel across the chamber to form a great pressure rise. The rapid pressure rise contributes to a power band's "Hit". In some cases the pressure rise can be so great that it causes an audible pinging noise from the engine. As the engine rpm increases, the pressure in the cylinder becomes so great that pumping losses occur to the piston. That is why engines with too much spark advance or too high of a compression ratio, run flat at high rpm.

Retarding the timing will make the power band smoother in the mid-range and give more top end over rev. When the spark fires closer to TDC, the pressure rise in the cylinder isn't as great. The emphasis is on gaining more degrees of retard at high rpm. This causes a shift of the heat from the cylinder to the pipe. This can prevent the piston from melting at high rpm, but the biggest benefit is how the heat affects the tuning in the pipe. When the temperature rises, the velocity of the waves in the pipe increases. At high rpm this can cause a closer synchronization between the returning compression wave and the piston speed. This effectively extends the rpm peak of the pipe.

Retarding the timing is one of the easiest procedures you can do and it's free. Try it before you do anything else.
 
W

whyz

~SPONSOR~
Nov 18, 2001
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would you have to remove the cylinder head to attach a dial gauge to it?and rotate the magneto rotor until the piston reaches TDC? Or am i totally off on the subject? I'd like to see if my timing is right and have no clue on how to do it the right way.. :think thanks...
 
L

LWilson250

Member
Jan 1, 2001
683
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I just want to say thanks, I will try changeing the timing on the bike asap. I will also look into getting a lighter flywheel weight, maybe a 9 or 10oz. one. I have lots of work to do!

Thanks again.

Lee W.
 

MX-727

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Aug 4, 2000
1,810
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I recommend Eric's more better everywhere porting and the V-force reeds. I have a '98 and the hit was smoothed out and I gained quite a bit more over-rev. The bike is a blast to ride. I'm going to end up selling it, but it is a great bike.
 
L

LWilson250

Member
Jan 1, 2001
683
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Well I rode it around a little today and I now am sure I am in over my head. I don't know what made me think I could ride this bike, I plead insanity. Maybe I will go back to a 4-stroke, maybe I will try and get used to this one. I know 2 rides isn't enough time to tell anything about the bike, that’s why I will give it a few more weeks. I think I was suffering delusions of adequacy when I bought the bike.

Lee W.
 
B

Blue Thunder

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Dec 20, 2000
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Lee..don't sweat it..I made a similar transition from an XR250 to a KX250..it will take some time to get used to the response and available power..if you have the space..take it out and just flog 2nd and 3rd only..practice some starts and play around on it. I know those 98's have boost but you will get use to it. Once you see where the power is the smoothest..that's where you will ride it..you will probably be riding it a gear higher than you did the XR..it helps bunches. Stick with it and play around on it..hills will be lots different now! Enjoy.
 
J

jharmon

Member
Aug 1, 2001
155
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I would leave the bike alone. I have a 1993 KX 250 that is a beast too. I was scared to death, when I first got it this past summer, but after a month of riding I felt really comfortable on it. It may take a while to get used to, but once you do, the power is definitely nice to have. I also ride tight trails, but like I said, once you get used to it, you'll be able to throw that bike around pretty well. And this is coming from a guy who's only 5'5" and 170lbs. You'll love the power!:D
 
T

troy2

Member
Oct 23, 1999
70
0
Lwilson,
Don't give up! I felt the same way, probably would have traded it after the first trip into the woods but I knew that wouldn't work with the wife. Do the mods I suggested and ride it everytime you get a chance. You will be amazed how quickly every thing improves.

Steve
 
B

bscottr

LIFETIME SPONSOR
Sep 20, 2001
1,255
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You're OK....

Lee,
You're OK! It'll just take a few rides to get used to it. You have some very knowledgeable folks that have given you some great advice, read each one, apply what you can right now and ride some more. If you're not satisfied in about a month call Mr. Gorr, you'll be glad you did.
One thing that helped me control my '01 in the tight stuff was to install a 50 tooth rear sprocket. I'm not sure what your '98 has on the back end, but you may increase the size of the rear by two teeth.

Keep us posted,
Scott
 
L

LWilson250

Member
Jan 1, 2001
683
0
Well guys, I have been talking to my friend Lacy Jones and she is going to help me learn to ride the green beast. Lacy has been riding for 20years and rides a 99 CR250 right now so she knows her stuff. I am going to order a gripper seat from MXSouth and maybe a FWW. I really want to thank you guys for helping me out, I really want to be a good rider and I just got bummed out when I got on the bike and crashed it in 5 minutes. But with your help and the help of my friends here I am set. If it doesn’t rain tomorrow I am going riding with Lacy, I get to learn from an A class racer! Well wish me luck!

P.S. what weight flywheel weight should I get?


Lee W.
 
L

LWilson250

Member
Jan 1, 2001
683
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You have a KX310???!! How did you manage that?! What is it like to ride? Hmm, more power, not what I need... I better just learn to ride what I have... Be happy with what you have, thats my mom always says... But mmmm more power...

Lee W.
 
B

bscottr

LIFETIME SPONSOR
Sep 20, 2001
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I just got bummed out when I got on the bike and crashed it in 5 minutes.
Click to expand...

Lee,
Somedays I crash in the first 5 minutes...and every 5 minutes afterwards! ;)

You were comfortable on your XR because you had two years on it. Before long you'll be roosting with confidence on your KX. Keep us posted.

Mr. Gorr currently has my head and cylinder, making it a 265 with Mo Better porting. I can't wait to get it back. You're right, Senior's 310 must root!

Scott
 
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