KDX - Shortcomings as a Dual Sporter?

SS109

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Jul 27, 2009
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I have heard mention that the KDX200 is not a good candidate for dual sporting. Supposedly holding it at high speed while street riding is potentially lethal on the engine when you let off the throttle and engine brake it. Right?

I have had three Yamaha RD two stroke street bikes and all ran great with no problems. I rode at speeds of 55-60mph on 60+ mile drives regularly with no ill effects. BTW, two of them were stock running oil injection and the third modified one I ran premix.

So, is it the gearing of the KDX or what that makes it bad as a potential dual sporter? What is the problem or design limitation with these bikes?
 

geoffro

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Nov 16, 2007
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use it

Don't believe what everyone tells you! There is so much "hearsay" on the internet it is frightening.Especially from people who are not mechanics! I am one by the way.
PS. My RD350 was one of my most fun bikes!if only it didn't have "scooter type" power under the powerband! :laugh:
 

dirt bike dave

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May 3, 2000
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I've dual sported a '90 KDX200 and a '91 KDX250. Rode them as much as 250 miles a day; did many dual sport rides at 100 - 150 miles a day.

If your dual sporting consists of high speeds and highways, a 200 or 250 two stroke gets tiring to ride. While you can gear it for top speeds in excess of 75 mph, cruising at 55 is PITA.

For connecting trails via short stretches of road, a KDX is a great choice if you don't mind pre-mixing.

I did blow up the bottom end on my CR250 when I rolled after the throttle after 2 miles of top gear WFO on a dirt road. The CR250 seems more prone to this than the KDX.
 

ws6transam

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Nov 17, 2005
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Hmm.... Dave is right. They make for nice lil' dualsport bikes, assuming your ride on concrete is moderately short: i.e. 50 miles or less.

I just did a 60 mile "cruise" with a whole passel of Harley Davidsons last weekend on my plated, air cooled '92 Yamaha WR500. Lots of 35MPH to 60 MPH stuff, no problems, except for the fact my butt got sore after 90 minutes and my fingers went all tingly from the vibration. The vibration also destroyed my mirror, which metal fatigued at the base and fell off onto the road. However, I then took it a few days later onto the trail system, and ran 3 1/2 hours worth of sand & whoops with no problems. One issue I have is that it sounds like it's going to break apart when cruising at low speeds. I think it's the low reciprocating mass of the engine: It's designed to rev fast & hard, not lazily cruise at one speed. Therefore, a flywheel weight might smooth things out for a more comfortable cruise. So far, I've got 300 miles of street duty on the machine this summer.

I also once had an early 80's IT250 that was plated, and it made for a fine dualsport bike, until someone stole it off Patrick AFB!
 

samiam

Member
Jan 3, 2000
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SS109 - I don't know, but I fully intend to find out for myself. My newly acquired 2004 KDX200 has a Baja designs kit already installed, but none of it works. I intend to get it straightened out and have it on the road, and inspected, before too long. My last KDX (a 1996 model) had a VT plate and I rode it on the road a bit. I had the bike geared down a bit to close up the gear ratios, but it still did fine on the road as long as I stayed on secondary roadways.
My CR250 (1994) and my CR500 (1995) needed a 6th gear.
 

reepicheep

Member
Apr 3, 2009
670
2
IMHO, buy a street bike and keep the KDX for the dirt. I tried the dual sport thing with the KLR-250. It was a fun diversion, but by the time I paid to keep it plated, insured, and kept replacing knobbies that were chewed up from the street, it got to be an overpriced form of entertainment. And I rode booring on the dirt, as I was afraid I would break something I needed on the street and I was 50 miles away without a truck.

A good street bike is SOOO much better on the street then a dual sport, and a good dirt bike is SOOO much better on the dirt then a dual sport.

IMHO, YMMV, and this was for Ohio where the closest off road places to ride are still at least an hour away. If there were long dirt or gravel roads around here, the dual sport would probably make great sense.
 

dirt bike dave

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May 3, 2000
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Another problem with a two stroke dual sport is that is does make more smoke than other bikes.

Some people (even other dual sport riders) will think you must be breaking some sort of law, and occaisionally they will approach you. All but a few will back down when you explain the law treats your bike the same as if you were on an XR, but some people like to argue.

Also, on my KDX250, when trying to sustain a cruising speed, the power valve would 'hunt'. Basically, even though the throttle was steady, the powervalve would start to open and the bike would begin to speed up. When no more throttle was given, it would slow down. Repeat cycle every second or so. It's not a problems when you are accellerating or de-cellerating, but it got annoying on long stretches of road.

Essentially, the more paved road and the higher speed of travel, the less suitable the KDX is. For 95% dirt/5% pavement, it's a reasonable choice. For 50% dirt/50% street, I'd look to something like a dualsported dirt version of a DRZ400. For 10% dirt/90% street, I'd want a big bore four stroke that was street legal from the factory.
 

samiam

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Jan 3, 2000
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I have to agree, to a point. I own a DRZ400S, and as much as I like the bike for my 3 mile commute to work, it is just too heavy for any serious woods work. This is where the KDX comes into play. IMO - both can be suitable dual sports. The DRZ is better on the street, the KDX is better in the dirt.
 

Joburble

Bring back the CR500
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Jul 20, 2009
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SS109 said:
I have heard mention that the KDX200 is not a good candidate for dual sporting. Supposedly holding it at high speed while street riding is potentially lethal on the engine when you let off the throttle and engine brake it. Right?
Engine braking on any premix 2 stroke that you have just had flat out for a few minutes is crazy. Firstly the motor is nice and hot and needing lots of lubrication and cooling both of which are supplied by the fuel/air mix. If you try and engine brake from high speed you are cutting off the lubrication and cooling when the cylinder, piston, rings, big and little ends need it most. It's even worse if you are riding at sea level (like on the beach) because the bike is already running lean. If you want to dual sport your premix 2 stroke, be kind to it, blip the throttle to lubricate it on the downshifts and get it stopped ASAP on the brakes. You can also have your idle set just a bit higher than usual to keep it lubricated when you are off the gas. You cannot compare it to a Yamaha RD or any other road bike, the motors are simply designed for different things. Nor can you compare it to a big bore 2 stroke that will do just about anything and still ask for more of whatever you can give it.
I rode a YZ125 2 stroke for years, including riding flatout on the beach without any probs because I was kind to it when slowing down. I sold it to a friend who rode it without probs until he took it to the beach and treated it like a 4 stroke when downshifting. It was obvious it was going to seize just by the way he was riding it, and it did.
 
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sr5bidder

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Oct 27, 2008
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old yamaha 2 stokes are very strong and have the oil injection wich helps them stay alive as the oil is injected it is able to lube in a more direct way to the bottom end.... you think thats why the kdx220r (streetable) in europe in oil injected?
I rode mine for 12miles from williamson wv to Matewan on the street after spending about 5 hours on the hatfield McCoy trails. I was very carefull and as been said it did not like a steady rpm the engine wants to be either accelerating or decelerating.

I just got finished rebuilding a victim of that road (cr85 big wheel) and could not find the big end needle bearings anywhere...they where GONE. I know the cr85 and the kdx are very different bikes but they are actually closer than an yamaha rd and a kdx.

that said the kdx would make an excelent country or in town bike 35-45mph for short trips between trails or to go get a six pack but still never as good as a xl600,650 klx or yamaha xt600 or xt350 untill you get back to the trails..then its shine time for the kdx
 

theckeler

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Feb 1, 2009
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I'm interested in this thread since I just started getting into DS rides with my KDX200, did one so far but plan to do more. Quite a few of the roads where dirt but a few where paved but short.
 

SS109

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Jul 27, 2009
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Some excellent points and suggestions. Thanks for sharing them with me.
 

Feral Donkey

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May 23, 2009
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man, last week when I was out in SD we went to a off road vehicle park called Farmington. It's between Wall and Rapid City in the Buffalo Gap National Grassland. We were on the 650s and we went up and down the big hill in the photo and then we left. I was thinking the whole time that I wish I could have found space on the truck for the KDX too. Man, that would have been a hoot with the KDX!

farmington3Large.jpg


farmington2Large.jpg


farmington1Large.jpg
 

adam728

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Aug 16, 2004
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Like most people here that dual sported a KDX, I found mine obnoxious on the road. After mods mine put up a respectable 81.2 mph on GPS. It was horrible if trying to cruise at anything over about 48 mph (powervalve opened shortly there-after). I could go into all the details about it, but I think everything's been pretty well covered here.



My bike spent most it's time in the dirt anyway, cept some commuting during a short stint in Georgia.
Picture963.jpg

JeepBike.jpg

KDXPinal.jpg
 

SS109

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Jul 27, 2009
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adam728 said:
...After mods mine put up a respectable 81.2 mph on GPS...
Please do go into details. What mods did you do?
 

adam728

Member
Aug 16, 2004
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Marana? I live by you....

Anyway,
  • Fredette Racing Products (FRP) cylinder porting
  • FRP reshaped head
  • FRP carb bore
  • FMF rev pipe
  • FMF Turbincore II
  • Boyesen Super Stock reeds
  • Chopped airbox lid
  • Twin air filter
  • Obsessive-compulsive jetting
  • 49 tooth rear sprocket (up from the stock 47)


Stone stock my bike put down 71.9 mph on GPS. After a few months I tore it down and found the anti-rotation pin for the ring had backed out of the piston and sawed a huge groove in the cylinder. Luckily I had a 6 month warranty, so I got all new parts, then promptly send everything to Fredette (it was winter in Michigan). When I got everything together I knew the bike revved much further than stock, but I figured that it would all equal out, more revs, shorter gearing, same top speed. Boy was I wrong.

I threw together a spreadsheet to calculate speed based on rpm and about any gearing combination. This showed my that stock my 220 ran outta umph in 6th at 8,400 rpm. Modded? 9,600 rpm to reach the top speed I saw with the gearing I was running. Massive difference.
 

SS109

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Jul 27, 2009
310
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Thanks for sharing that.

Yep, we are fairly close to each other. Maybe when I get all my gear sorted out we can hook up and go for a ride sometime.
 

adam728

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Aug 16, 2004
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My last AZ ride was a couple weeks ago. Gear is packed, bike is drained of fluids, this weekend I'm packing, and next week we move to Arkansas. Job transfer.

You ride the single track stuff in Marana? The "regular" loop sure got destroyed this year. :(
 

SS109

Member
Jul 27, 2009
310
0
Good luck on the move and the transfer.

As far as riding, I have been out of things for quite sometime (18 year hiatus!) and I'm just now getting back in to it. I'm in to single track riding but haven't been out scouting places to ride just yet. I know a MX kid that nows of a couple of spots near Ironwood that he says I would like but haven't had a chance to check it out. Do you have any suggestions on good places to ride around Marana?
 

Kurt Franz

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Apr 8, 2008
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Have my 2004 dual sported and it is ok to cruise at about 50-60 mph for as long as you want to. I had to change the pilot jet on mine from the stock 48 to a 42 as it was sputtering and spooging realy bad when trying to ride at slow steady speeds. Other than that it is all stock and I run it a 32:1 per the owners manual.

I find the sweet spot for cruising to be right around 55 mph where it will run smooth and get about 40 mpg. Once you start getting on it the mpg will drastically drop - you gotta ride it like a grandma to get good mpg.

I did not have any issues with the seat and the longest ride I took was 200 miles all paved and some dirt roads. Good dual sport tires also make a big difference.

I have a Garmin GPSV mounted on the handlebars. Provides my speed and odometer. The GPSV is an old model, but very well built and waterproof. It will store enough maps for most of your rides. I found mine on Ebay for $50.

The bottomline is that the bike will go wherever you take it. It aint gonna explode if you ride it at a constant speed - provided it is jetted correctly and well maintained. Also, I am skeptical about engine braking after long sustained high speeds and the engine seizing as I have never seen it happen and I have seen many guys abusing their 2 stroke bikes in this matter. That is your call - but I engine brake just like I would on a 4 stroke with no ill effects.

Take most of the stuff you read on these forums with a grain of salt - as some of the people posting are just regurgitating stuff they have previously read and want to come across as knowing something - when actually they know very little and just spend time buying worthless accessories for their bikes and posting about the next mods, admiring their spotless bikes, and riding very little.

Take the KDX out on the highway along with a bottle of Yamalube R and have at it - and come back with the real world results.....lets have some more valuable real life information. I think you will find that it is capable on the road and well worth the ride when you arrive at the trail head.
 

Joburble

Bring back the CR500
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Jul 20, 2009
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Kurt Franz said:
Also, I am skeptical about engine braking after long sustained high speeds and the engine seizing as I have never seen it happen and I have seen many guys abusing their 2 stroke bikes in this matter. That is your call - but I engine brake just like I would on a 4 stroke with no ill effects.

Take most of the stuff you read on these forums with a grain of salt - as some of the people posting are just regurgitating stuff they have previously read and want to come across as knowing something - when actually they know very little and just spend time buying worthless accessories for their bikes and posting about the next mods, admiring their spotless bikes, and riding very little.

Take the KDX out on the highway along with a bottle of Yamalube R and have at it - and come back with the real world results.....lets have some more valuable real life information. I think you will find that it is capable on the road and well worth the ride when you arrive at the trail head.

Like I said, if you ride it flat out for a sustained period at sea level and then engine brake to slow you down the REAL WORLD results may be a rebuild. Your scepticism would not have rebuilt the motors that I have seen seize doing exactly this, but REAL WORLD cash was actually used. Provided that you are not cruel to a motor of course it can be ridden pretty much anywhere, but be kind to it is all I am saying. And where is the harm in that. Constant speed is not the issue, it's the speed of the constant speed.
 

dirt bike dave

Sponsoring Member
May 3, 2000
5,349
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As mentioned before, I did blow up the bottom end of a CR250 using engine braking after a sustained 2 miles or so of top gear WFO. Hot motor + high rpm resulted in big end and crankshaft bearing failure when the cooling fuel and lubricating oil was reduced. Took out one of the cases. It cost about $1,000 to repair.

I've dualsported KDX's for thousands of miles and never had a problem, and the KDX may be less prone to failure than other bikes. But after the expensive experience with the CR, I'll just pull in the clutch from now on if my pre-mix 2 stroke motor is red hot and I need to slow down.
 
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