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KDX 250 motor?

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Posted by: 97 moto---------------------

I just purchased a 92 KDX 250 that is excellent condition.I was wondering if the motor is a KX with just different gearing? If so will the boysen rad valve for a kx work and help out much. I'm in the process of putting an FMF pipe on. Also Is there a reason why Kawasaki quit putting this motor in the KDX?

Thanks for any help

97-moto
staltr1@mindspring.com


Posted by: flyinfish---------------------

I talked to an engineer from Boyesen a while ago about putting a KX (Rad -12) Rad valve on a KDX (Rad - 12x). He said the reason for the difference in valves was because the difference in compression and breathing between the two motors. He said the difference in the valve was basically the size of the bore leading to the cage. Seems to me that if you've done any mods ie. porting or raising the compression with a KX head gasket maybe the KX Rad would be appropriate. Try giving them a call and see what they think.


Posted by: spanky250---------------------

Quote:
Originally posted by 97 moto
I just purchased a 92 KDX 250 that is excellent condition.I was wondering if the motor is a KX with just different gearing?
It is basically a '89 KX 250 engine with a wide-ratio tranny, heavy flywheel, lighting coil, milder porting, and lower compression. The carb is smaller, also. Nearly every part you order for the engine is a KX 250 part, even though they will have a different part #.
Quote:
Originally posted by 97 moto
If so will the boysen rad valve for a kx work and help out much.
I tried the Rad Valve, and was very dissapointed with the improvements in relation to the price of the Rad Valve. I feel that the two-stage Power reeds in the stock reed cage had more effect, for far less money.
Quote:
Originally posted by 97 moto
I'm in the process of putting an FMF pipe on.
The FMF pipe that you want for this bike is the K-24. In combination with a good silencer (I alternate between a Powercore and a Turbine Core),it will transform the power so much you won't even think it is the same bike. The low-end will be about the same, but it will seem weaker, because the midrange will be so much stronger than stock. 4th gear wheelies will be just a handful of throttle away.

If you really want to get some performance out of that engine, rejetting is a must. The jetting is so far from correct that the bike is virtually unrideable in slow stuff. My best solution was a leaner slide.That engine is also in a very mild state of tune, with tons of untapped power. Get a KX head gaset (they are thinner) to start, and porting does wonders for it.

For tight woods, the stock gearing is too tall, forcing you to use first gear way too much. A 50 tooth rear made second and third much more useable.
Quote:
Originally posted by 97 moto
Also Is there a reason why Kawasaki quit putting this motor in the KDX?
They stopped making the KDX 250 in '94, it just didn't sell. Woods riders bought the 200, and motcrossers bought the KX 250. Kawasai did a poor job of selecting the fork spring and damping rates, and the seat-to-tank junction, making for poor handling without some work. As a result, this pretty good bike just got ignored by most riders.


Posted by: Tantrum---------------------

Nevermind. I had a question that I realized was very stupid AFTER I posted it.


B.


Posted by: 97 moto---------------------

Thank you for the help. I appreciate the information.

Thanks

97 moto:D


Posted by: Speedy---------------------

Hey Spanky,,, What else did u do to it?? im thinking of buying a 92' KDX 250 and im worried about the weight difference(i have a 200)and if it is worth all that weight to get 250 cc's,,Not sure though?? i Have some money saved and want a 95' or newer 220 but i have a good connection on a 92' 250!!! Can u change my mind ??? Let me know -Speedy


Posted by: spanky250---------------------

Quote:
Originally posted by Speedy
Hey Spanky,,, What else did u do to it?? im thinking of buying a 92' KDX 250 and im worried about the weight difference(i have a 200)and if it is worth all that weight to get 250 cc's,,Not sure though?? i Have some money saved and want a 95' or newer 220 but i have a good connection on a 92' 250!!! Can u change my mind ??? Let me know -Speedy
It depends on your riding conditions. In more open areas, I can walk away from a 200. The tighter the trails get, however, the more the advantage swings to the 200. When it's really tight and snotty, I can't use my motor advantage, so the 200s superior handling tips the scales in their favor. The 200 can't come close to the horsepower or the low-end grunt that this engine has the potential to make, though. If power is your thing, the 250 has it, once uncorked and tweaked. My engine is ported, I run a titanium rod and Wiseco Prolite, and I have two-stage reeds and an FMF exhaust. Stock, the KDX 250 D made around 32 horsepower ( about what a breathed-on 200 can make ). In current tune, I am making approx. 40 horsepower, more than enough for woods work. Where this engine shines is in the low-to-mid grunt. I can climb anything, just point it and let the engine do the rest. I can grunt up hills in second and third that 200s have to get a run at and scream up in first and second.

On paper, the 250 is only a few pounds heavier than the 200, but when riding it, it feels heavier. It is a big, stable, slow-handling bike.


Posted by: Speedy---------------------

Hmmm,,,, I see....... So i guess u have prolly stripped it down so its as light as it can be huh? And how is the suspension??? I ride In MIch. Theres alot of tight stuff and open stuff... But thanx fer the info u already gave me!!


Posted by: spanky250---------------------

There isn't a whole lot you can do to make it lighter, the frame is the main offender. Chunking the stock boat-anchor exhaust system will take a couple of pounds off, but beyond that, you just have to learn to adapt.

In stock form, the suspension has the same front-to-rear balance problem that the 200/220 has. The shock is sprung for a 200 lb rider, while the fork is sprung for a 140 lb rider. Toss the stock .035 kg/mm fork springs, and get some .040-.042s, depending on your weight, and the difference in control and handling is dramatic, especially in rough stuff.

My father-in-law lives in Michigan, so I have seen the trails there, and they are similar to conditions here, just not so mountainous. Here, the steep hills in the mountains give me an advantage over 200/220s, but without them, in the really tight stuff, the 200/220 is easier and less tiring to whip around in between the trees. The 250 is also limited in aftermarket parts availability, and things such as shrouds and side panels are difficult to get and expensive to replace.



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