Int'l SR model KDX200

Int'l SR model KDX200

The SR is basically a milder version of the R model with more stuff for street use (speedo, turn signals, ignition key, etc). Less power is available due to a smaller carburetor (28 vrs 35mm) and air filter, possibly different port timing emphasizing low end power, and an exhaust pipe with more "insulation".
Steel versus Plastic Gas Tank
The SR has a steel gas tank which can get very hot from the hot air that comes from the radiators. That can decrease performance by making the gas hot. Note that the mechanic of Ricky Carmichael puts heat reflective aluminum foil on the underside of the tank and will sometimes put the gas tank (with gas inside) on ice in between motos. To remedy the problem you'll need to clean the tanks underside, apply a layer of silicone sealant, and then apply a layer of thin 'bubbly' packaging material so that the trapped air bubbles in the material will provide the most insulation. One person on the dirtrider network reported that his used SR came with a plastic tank. So maybe it is OK to replace it with a standard KDX tank although the rear connection is different (as is the filler cap and fuel petcock). I think the rear mounting post would have to be sawed off.
Exhaust pipe
The first thing to do is replace the exhaust pipe since trying to take the insulation out of the body of the pipe (not the header. see and click "tech tips", then "pipe mod") is a very extensive project since much more of the pipe is insulated compared to a R model. FMF has pipes for better low end and better top end (35 (torque) or 30 (rev) gnarly series pipes) but many have complained about quality control problems. I chose to use the Pro Circuit pipe which enhances the high-mid and top end power. The SR has bolts for pipe connection at the header, not loops for spring connection as the R model has. So I used those bolts on the cylinder to hold in place loops made from a heavy duty wire. So after buying the springs I was all set. For spooge-free connection I use an exhaust pipe o-ring between the cylinder and the pipe (not around it as is normal).
Reed valves
Next things to do is replace the stock reed valves with high tension carbon fiber reeds (from Boyesen or Carbon Tech) because they are lighter and open/close faster which allows more air/gas charge in the engine. I bought the low tension reeds and they often made a fluttering sound, so I backed them up with cut down sections from my old reeds to give them more tension which makes them more mid-high reeds than low end reeds. I'll replace them with high tension reeds later.
Increasing air intake and preventing water intake
Taking off the stock "snorkel" allows more air intake but also will allow muddy water in (that gets splashed up there) which can cause your throttle to stick open. People do it to allow more air in which aids power output. But the snorkel is there for a reason. Too bad they didn't design it with a more voluminous intake. Once the muddy water cascades into the air box the air filter will pass it in because it only catches "dry" dirt particles with the air filter oil. The muddy water gets up there when it gets tossed "up" there while you are splashing through muddy water. My solution is to toss the restrictive snorkel and cut out a bigger rectangular hole. Then use something (I used cut out pieces from a quart sized mineral water bottle) that you can duct tape them in place to build a 1/2" tall "wall" around the big hole to prevent creeping water from coming into the air box. Also you'll need to duct tape the front edge of the cover to the air box. Also run a piece of duct tape from the left frame tube to the right one (taping to their undersides) in front of the air box which makes a splash guard there. Also tape the right upper side of the air box to the frame, effectively making a splash guard for that vulnerable side. These two mating surfaces let splashed water in. Also put a plastic splash guard under the area that's open between the tank and the frame. Also if you ride through deep streams you should silicone seal the air boot to air box juncture. If you have already drilled holes in the air box lid for greater air flow then this fix won't work for you and you'll need to buy another lid (they are cheap enough) and do it right. After all these fixes my air box still would ingest a little muddy water (but much less than before) from going through muddy puddles. So the final refinement was to put a piece of cardboard (sealed from water by putting packaging tape all around it) from the forward air box opening (secured in place with duct tape) to the near-bottom of the air box which basically provides a "chute" for the water to go down without getting onto the filter. Also I made the sides of the cardboard (about 3/8") bend up by 90 degrees (and held in place with tape) so that water won't get sucked over the sides of the cardboard and onto the filter. That way it just goes all the way down to the bottom of the air box. I finally put my noggin to work on this problem after I lost the last MX race due to the throttle sticking open with dirty water getting in. It was disappointing because I was going to win and it was going to be my only win of the year. I got 2nd place the first moto and then pulled off the track with this problem while in 1st place in the second moto. I was all prepared except for this one weak spot - water intake prevention. Also I've put silicone seal on the top of my carburetor to keep water getting in there where the cable sheath rests against the carb top. There's a rubber boot there but I think water could still get in.
Modifying the carb slide leaner
Jetting on my carb is now 42 pilot and a 128 main jet (adjustable). The needle jet on an SR (the female part) can be adjusted up (leaner) or down (richer). I set mine in the leanest (highest) position and dropped the needle to the lowest (leanest) position but still found it was too rich for the first 1/4 opening. (probably due to the needle becoming thinner with wear from vibration over the years.) So I cut away the carb slide a little. I widened the "tunnel" by a couple mm on each side on the bottom edge which allows more air in that isn't directed to the needle jet which makes it leaner. Keep in mind that my elevation is around 1000 ft and its hot as the desert here which means leaner is necessary. If you are at sea level or live in a moderate-to-cold climate you may not need to modify the carb slide and you may need a main jet near 135.
Ignition Timing
My '89 model has ignition timing set at 21 degrees BTDC whereas the years after had it set at 19 (with a resultant 1hp gain on top). After hearing that you can change it (if you have a flywheel puller and holder) to enhance performance I experimented by advancing the stator one notch CW and then CCW. CCW gave dull low end performance with just a little more power on top (but nothing significant), and adjusting it CW (advancing the spark) really gave it more umph in the low and mid range without detracting more than a little bit from the top. With it advanced I really like the increased power although it runs a little hotter. So with this mod you need to have a clean cooling system (use radiator flush) and use 50/50 antifreeze/distilled water to prevent coolant loss due to boiling.
Piston skirt mod
This mod is to help intake flow from bottom dead center to where the skirt raises enough to allow air/gas flow under it from the reeds. This is done by drilling a few holes in the intake skirt. The stock piston has one hole in the middle with its center 38mm down from the piston top. I enlarged it to 3/8" (9mm) diameter. I also made two holes 3/4" (19mm) to the left and right of the intake centerline and 34mm down from the piston top, that have a 1/4" (7mm) diameter (which I may enlarge to 3/8" (9mm) diameter). And I made one little hole in the centerline (22mm down) with 3/16" (4.5mm) diameter to aid circulation under the piston crown which combats heat buildup there. The 3 main holes help with mid range power (to the best of my knowledge).
KIPS and compensative engine mods
The power valve system on earlier years had a problem with valves breaking or the gear teeth stripping out. I was replacing mine twice a year so I just glued them (the two side aluminum valves) in the "open" position with epoxy glue. The middle valve still works well since it's made from steel. That change caused some low-to-mid range power loss but I got that back when I had the cylinder custom sleeved so that the top of the 3 exhaust ports were .7mm lower. Also I removed the thermostat valve in the head which is supposed to open when the engine gets hot. It was stuck in the open position. Even if it worked it might be restrictive to coolant flow when it's open (compared to the R model which has no regulator).
The final result with my bike is that it has a very progressive powerband with decent power all through the rpm range without a strong "hit" when the power valve opens (which is desirable for the street). And it is strong enough to do well on the MX track, where in some instances it really shines when it's in the middle of the powerband and I don't have to clutch it to be able to accelerate.
Stage II engine mods
To further enhance the mid range and low end power I had the cylinder resleeved with a .7mm lower exhaust ports at the top edges. The sleeves from LA Sleeve come pre-ported, so I didn't use theirs. The shop here uses non-ported sleeves and they make the windows in it to match your current porting. So I just asked them to do that and they did. And man, what a difference! So much more low and mid power that it almost feels like an open class bike. I left the 15/49 street sprockets on (whereas 13/49 is for MX) and went to practice on a tiny MX track I have. I was able to sometimes keep from downshifting going into turns and rarely had to use the clutch coming out of turns. And I was cutting faster lap times than I had before while using 13/49 sprockets! I am really impressed with this mod. And it still has worn out piston rings in it. Scroll down past the carb update to "engine parts" if you don't want to read about carb changing. Since resleeving is not a considerable option for most people then all that is left is to lathe off that .7mm from the bottom of the cylinder and add a .5mm-.7mm thick aluminum head gasket which can be made in your own garage.
Carb Update
The R year models of '87 and before had a 34mm Mikuni carb (VM34), and afterwards had a Keihin 35mm carb (PWK35). The SR comes with a 28mm Keihin carb (PE28). Updating your bike with a larger carb will increase the mid-to-upper RPM power output. The 34mm Mikuni may tightly fit into your present carb boots. If not then you'll have to spend $201 more for boots. The 35mm Keihin carb is a better performance carb but also larger and you'll definitely have to spend the extra $201.

Dimensions (outlet dia., inlet dia., distance inlet-to-outlet, height) in mm:
     outlet inlet distance  height
PE28  34     48       82 
VM32  40     58       83    142
VM34  40     58       93    137
PWK35 42     59       91    153 
Larger Mikuni Carb $90
From Amazon (OEMCycles): Mikuni VM34 (with 260 main, 35 pilot, Throttle Slide 2.5, Needle 6DH4, Needle Jet Q-2)
(stock jetting for ’87 KDX200R: 320 main, 25 pilot, CA.3.0 slide, 6FL52 needle, R-2 needle jet)
(Jeff Freddette recommends: 330 main, 30 pilot)

VM34 Parts/ Kawasaki part #’s / price
330 main 92063-048 $8.63
320 main 92063-047 $8.63
30 pilot 92064-022 $8.42
25 pilot 92064-032 $8.42
CA 3.0 slide 16025-1114 $86.79 (you can also just cut .5mm off the lower angled part of the 2.5 slide to be like a 3.0 slide)
R-2 jet for needle 16017-1307 $23.23
R-0 jet for needle 16017-1309 $17.37 (this is preferred if you keep the unmodified 2.5 slide)
6FL52 needle 16009-1226 $23.82 (not available from, only from
throttle cable 54012-1305 $18.62

The VM34 carb, recommended main jet, pilot jet, needle, and needle jet totals $154 w/o shipping cost.

(The carb image is of the VM with a right side idle air screw. The VM34-168 from OEMCycles has a left side air screw.)


The rubber boots before and after the carb and the air filter parts may have to be changed also since the Mikuni intake throat is 10mm larger and the outlet throat is 6mm larger. Following is the parts listing:
Carb to reed boot 16065-1181 $40.53
clamp 92037-1843 $4.10
air filter duct 14073-1362 $48.08
air inlet duct 14073-1363 $19.22
air duct plate 13183-1046 $10.68
clamp 92037-171 $4.32
air filter base 13091-1594 $18.01 
air filter frame 13091-1454 $27.11
air filter 11013-1196 $24.73 (a TwinAir filter from RockyMountainmc is $27)
Total: $196.78
(new holes may have to be drilled in the airbox to match the mounting holes of the new boot)

Larger Keihin Carb

Keihin PWK35AS $227 #016-197 (with customized jetting) from
(jetting for ’89 KDX200R: 158 main, 48 pilot, CA6.0 slide, R1172N needle, no n-jet)
(jetting for ’94 KDX200R: 150 main, 48 pilot, CA6.0 slide, R1172N needle, no n-jet)
(jetting for ’95 KDX200R: 160 main, 48 pilot, CA5.0 slide, R1174K/2AFKQ needle)
                                                          (R1173K/2AFKP is leaner)
(jetting recommended by Jeff Freddette for an '89 to '94 with pipe/reeds/airbox mods is 
152 main, 45 pilot, R1173N needle, CA6.0 slide)
Kaw part #’s
165 main  92063-1370 $9.80
162 main  92063-1369 
160 main  92063-1368
158 main  92063-1367
155 main 92063-1366
152 main 92063-1365
150 main  92063-1364
148 main  92063-1363
145 main 92063-1362
142 main 92063-1361
52 pilot 92064-1130 $11.86
48 pilot 92064-1143
45 pilot 92064-1142
42 pilot 92064-1141
CA6.0 slide 16025-1148 $107.49
R1172N needle 16009-1523 $22.90
R1174K/2AFKQ needle 16009-1832 $25.00
R1368E needle 16009-1385 $22.63 (richer at idle and progressively richer to open compared to R1172N)
R1369E needle 16009-1386  $18.43
Throttle cable 54012-1360 $24.85

Engine Parts
Looking up the part #'s at for the SR, and for the R, I saw that the head, piston, rings, cylinder, base gasket, and cases were different.
Here's the part #'s:

Part         SR model   R model     prices for R model parts
----        ----------  ----------  -------------------------
head        11001-1301  11001-1291  $197
piston      13001-1290  13001-1295  $ 99
rings       13008-1110  13008-1116  $ 43
cylinder    11005-1585  11005-1569  $562
base gasket 11009-1817  11009-1994  $  7
cases       14001-5264  14001-5262  $460

Looking up the SR parts costs at I saw that the head, cylinder, piston/rings, and cases were not available. So they'd have to be gotten from the UK (contact although I have successfully used regular R model piston/rings, head gasket, and base gasket.

I emailed Howard Richards (, who is an experienced modifier of 2 stroke engines and owner of porting software, with the following information about my KDX200SR and an inquiry for cost of porting recommendations:
I mostly use my bike on the street so I need a smooth powerband. My 2 side KIPS valves were going bad twice a year so I just epoxied them in the open position. The KIPS valve in the main exhaust port still works. I have low tension carbon fiber reed valves but they fluttered too much and so I reinforced them with some strips from my old fiberglass reeds. Now they are more mid-range valves. I also drilled three 3/8"dia intake holes in my piston intake skirt to help out the midrange. So right now my bike has a smooth powerband but it's a little weak for MX. If I could get more power throughout then I'd be happy. I'd like your program to tell me what changes would occur if the second top of the exhaust port were raised 2-4 mm. Or maybe just from your evaluation you could give some recommendations. Of course I also need to swap out the 28mm carb for a 35mm carb (std on regular KDX). Please let me know what the cost would be.
he replied;

The ProCircuit pipe is not going to contribute to a smooth powerband, quite the opposite, but it will increase top end and upper mid-range as you predicted.
Exhaust port and transfer timings are slightly longer in the standard KDX cylinder (which means they are higher in the cylinder for better top end power).
The smaller carb will give you a smoother, wider powerband with less top end power while the larger carb will make the bike decidedly more "peaky" and deliver more high RPM output.
The epoxied open side KIPS valves will also make the engine peakier and reduce low end power. There will be no increase in top end by leaving them epoxied open, just less low end.... thus, also counter-productive.
The holes in the piston intake skirt will help slightly, but you must be careful not to weaken the thin skirt and break it off due to the propagation of cracks (it is the thrust side of the piston during the power stroke).
I would suggest measuring your current squish clearance as is outlined at and then sending me the required pieces when you (and I) are ready to modify the porting/head arrangement.
I would require the "used" base and head gaskets, cylinder, piston, head and exhaust manifold you are using with your current pipe. I will also require at least a $100 deposit. Porting mod's for a wide, general increase in power across the RPM band are $255. Head mod's to compliment the porting and generate efficient squish pressure/velocity with a compression ratio that is agreeable with your local pump gas octane is about $100.
Please ask any other questions that may come to mind.
regards, Howard Richards at

I replied:
Hi Howard
Do you have a price just for porting recommendations? I plan on having the cylinder resleeved and the shop could also do porting at minimal cost. I'll also play with retarding the ignition timing since the '89 model is timed at 21 BTDC whereas later models were set at 19 BTDC. I wish you could ride my bike now. You'd be amazed at the low and mid range power it has. I too thought that leaving the side exhaust valves open would screw the powerband but it didn't hurt it much. Maybe because they are small enough to not matter too much. I think the carbon fiber reeds, piston windows, and modifying the carb slide "leaner" all contributed to a better mid range.

Tires for dirt and street
The Pirelli MT21 front and back are very good and long lasting although not as "sticky" as hard terrain MX tires. They have a tread design that's 80% for dirt. If you like to MX on the weekends then maybe you'll want to use true MX tires. You can get away with doing that and still ride on the street (if the cops won't hastle you) if the rubber is soft which is the case when the tire is designated for hard terrain. The soft rubber is needed to grip the asphalt since there is less surface area contacting it with a knobby. I have used (for the rear) the Dunlop D739 and Maxxis Cross HT successfully. I normally get 6 months from the Dunlop after riding almost every day for about 15 miles on the street (half of that in town). The Dunlop is the best tire for doing power slides in the dirt that I've ever used. It really makes me feel like a pro since it only allows the rear end to swing out so far. The worst tire I've ever used on the street was a Kenda (D-760). It was very slick on the street. I've also used a Dunlop D773 which is a soft rubber mud tire but it was half wore down after only a month. The Maxxis has more of a round profile which is better for turning on the street. Its traction in the dirt and on the street is very good and it is wearing very slowly. But they changed the design somewhat for 2004 and now it has even more knobs (4 rows more I think) and they are less wide. So for now I recommend the Dunlop D739 for the rear. The best for the front are the Dunlop K490 and D739, and Bridgestone ED77 (or ED11 with harder taller knobs, stock on the YZ250WR) which are soft compound intermediate to hard terrain tires. They wear faster than the Pirelli MT21 but after falling a few times (front slid out) I decided buying tires more often was better than paying doctor bills.

Silencer cleaning
Here's a report from someone who took his apart to clean it out:
I cut the muffler about a quarter inch back from the manufacturers weld (at the exhaust pipe end).. I was careful not to cut any deeper than the thickness of the aluminum (about 3/32nds) this worked well though I would cut closer to the weld if I did another one (say 1/8). this allowed me to withdraw the end plate with it's location guide intact. If I had cut through the end to a greater depth I would have sliced the guide in half.
Next I drilled out the rivets at the in end (these hold the bowels of the muffler in place). I then had to saw off the input pipe to the muffler as the bend won't fit through the hole (it was obviously welded on after the muffler was assembled)
And slid the whole sorry assembly out of the muffler tube... Very simple and sweet design.. The muffler is divided in two. Slightly forward of the middle the gasses from the engine are piped through the first chamber and released in the second chamber they then flow back to the first chamber and are piped out to the world. (so they basically go round in a circle then come out)
This arrangement is surrounded by a perforated drum which is wrapped in fiber glass. The perforations in my drum were all partially blocked and many were completely blocked and the packing was fairly solid with carbon. No spooge at all. I tried a few options to open up the chamber and found the best way is to chisel out the four welds in the tail cap (this bent the cage a bit but it is easily straightened. With these welds broken the end of the drum came off and I could clearly see the guts of the system.
There is no real potential for this muffler to block up (which I was concerned about) The carbon seems to accumulate around the mesh drum and in the packing where it probably does not effect the efficiency of the muffler much at all.
In any case I cleaned out my perforations all gazillion of them replaced the packing (I used Chopped strand mat) and drilled a few judicious holes to aid the free flow of gasses. They told me in the shop that these mufflers are a bit restrictive.
Welded the whole thing back up .. no noticeable difference in power or sound.
My muffler weighed 2.1 KG when I stripped it and just over 1.8 when I re-assembled it.


Click here if you want to see my page just dedicated to mods for making the KDX200 better for motocross.