2015 SX250/TC250 Suggested Mods

You... know.. about adding more mix.... leans out... fuel mixture....... YESSSSS!!!!!!!! Finally! Someone who knows what the fuck is up, i do believe that the single ring can work just effectively as well, but keeping rings fresh,(for most, that just isn't what's happening) itle do just fine, I ran a single run in my 03 till it literally gave out and the bike wouldn't run anymore, and it still outpulled my buddy's yz250's right till
It gargled and farted to a stop.

With the pv settings, the slacker the spring tension is at rest, the sooner the valve will open, little secret on that too, call your local ktm or husky dealer, and get them to order you a 1.8mm primary spring and keep the red auxiliary spring, the stock primary spring from the factory on all the 125's 150's 250's and 300's is 2.0mm in wire thickness, the 1.8mm spring will open the pv even sooner in the rpm range, it will also effect when the pv is fully open as well.

Now let's talk dynamics of engine flow, and port velocities a bit, i believe the whole reason behind the classics 2 stroke "hit" is a late timed pv governor, so by the time the pv starts to open, it's too late in the rpm range to make a smooth transition, from low end to mid to top end, and the result of that late opening pv, is that the engine suddenly and abruptly gets the use of its exhaust port, and it makes for a very very steep power curve climb. By getting the pv to open sooner, the engine is able to flow at higher rates sooner in the rpm range, and therefor, will add midrange, and smooth out the transition between the mid and top end transition by Having more power sooner in the rpm range, so the rpm climb is smoother, and more linear in delivery. This gets hard to explain a bit, but just my theory, and from what Iv tested, has proven to be true. But if the engine can take advantage of the exhaust port being opened sooner, it will add power right off idle, if your port opens too slowly, and the engines flow rate is being restricted by the pv being closed too long, it builds up too much back pressure in the crank cases, as the engine is able to pull in more air and fuel than it can effectively use and expel with a small exhust port duration. by getting the pv to open at the most opportune time is vital for power delivery, as it works in conjunction with what the engine can produce for flow rates, so if the engines flow rate, and pv timing move in unison together, it will effectively remove the hit and abrupt powerband that is so very tiring, and harder to control. I have done this with more than a few bikes, my tc144 included, Iv actually got a yz250 pv spring in my governor now, it was 2mm taller, but drastically smaller in wire diameter, and I removed the inner auxiliary spring that was in it as well, it honestly feels like a 250f now. Iv done it with my 12 250sx never got the chance to use the 1.8mm spring though, as I didn't know about it at the time I owned it. I also did it to my 08 rm250, as the pv spring tension can be adjusted externally on the left side of the cylinder. I backed it totally off and, and then would go in 1/4 turn at a time on spring tension, till it pulled magically off idle, and was broad and powerful the entire way across the rpm range. 4 stroke mx bikes in the beginning, I hated them, and I felt that classic 2 stroke hit was quick as hell, and the superior power delivery, then... things changed, and 4 strokes started making more and more power, and started to leave 2 strokes in the dust. So I adopted different ways of thinking about how to tune 2 strokes not for peak numbers, they already make plenty of hp at high rpm, but it's filling in the bottom half of the rpm range to effectively broaden powerband and make a more usable power delivery, it took a while, lots of reading to figure out where things have gone wrong, and why 2 strokes were just being left behind after being so dominant for so long.

So here we are making changes for the better, I really appreciate this conversation, and what's been been said, super cool to talk with a fellow piston head and read about aspects I haven't thought of before, thank you for making my brainwork overtime!

Thank you for your really good tips how to broaden the powerband. I also really like to have this conversation with you as it has much more info than the normal way like how to get more power from a 250 => put 300 kit in it... =) I will try to get that 1.8 mm primary spring.

Edit: I already ordered this part number 54637072000 outer spring with wire diameter 1.8 mm.

I can fully understand what you write above. Very well explained and I believe also that the 2-stroke "hit"" comes from too late pv opening and the exhaust chamber tuning. Only thing that might be "wrong" after this mod can be the exhaust tuning. By this I mean how Bill´s Pipes exhaust are tested/tuned as it must have been tested with normal pv primary spring. But it can work also very well with this 1.8 mm spring who knows...

I asked many months ago here and on other forums about KTM/Husky 250 exhaust port height when pv is closed and when it is open because I wanted to calculate the exhaust port timing before I will take my own cylinder off and measure it myself. These calculations would be based to the assumption that piston is level at TDC. Stroke lenght is 72 mm so IF exhaust port height was lets say 24 mm when the pv is closed (one third from the total stroke lenght) and piston top would be level at BDC with the exhaust port bottom then the exhaust timing would be only 120 degrees. IF exhaust port height was 36 mm when the exhaust port (pv) is fully open then the exhaust port timing would be 180 degrees. I think that the "thruth" will not be very far away from these figures. No one has answered to that what is the height when closed/open but I will figure it out myself when I take my cylinder off. This change in exhaust port timing is very big. 0.5 mm change in pv flap height will have big effect. Also by raising the cylinder by 0.75 mm will have big effect in transfer ports and exhaust ports duration. I will first use that RK Tek head as it is now and order later another insert and raise cylinder to extend transfer ports and exhaust ports timing.

In pretty sure I was up over 1mm on base gaskets, I think around 1.2-1.5mm of base gaskets, but I'm not sure, and if you pull up the 250 ktm service manual, it has the spec for the resting height of the pv in it, so no need to tear down to find out, that's how I came to know the height. I'm sorry I can't recall the height off the top of my head, this was years ago I did it.

As for pipe design, I know that all the manufacturers of 2 strokes exhaust have their premise as to how they go about designing a pipe to work accordingly by manipulating the 5 sections of the pipe, to the best advantage. But when it comes to expansion pipe pressure, I feel that getting that pipe pressurized as soon as possible, to get the exhaust pulse return wave to gain strength and keep the pipe hotter for stronger exhaust pulses. I'm also in the mindset that an exhaust pipe is designed to be pressurized, and that the sooner you build up pressure, the sooner the pipe can aid in making power, but all just thoughts and speculations, that bounce around my head. But I gotta get to work! Give it a think and shoot back at me

I found this dimension from Husqvarna TE250 2015 Service Manual:

Z: (Height of control flap) 48 mm

I also found this good video about setting Z dimension in 250/300 KTM/Husky:
https://www.youtube.com/watch?v=AvLUSh_nHbY

When pv is in closed position exhaust port height is then 72 mm - 48 mm = 24 mm when dimension X (piston top from cylinder top surface is 0.0 mm = level at TDC). So if this Z dimension is adjusted for 47.5 mm (0.5 mm less) the exhaust port height is 24.5 mm when pv flap is in closed position. Did you have it set up like this in your 250 SX?

I´m not an expert of exhaust pipe designs so I have to just try how well Bill´s Pipes exhaust will work with these mods. Many other users have been happy with this pipe so I decided to get one.

That's exactly it resting is when the pv is totally closed. And as far as pipe selection goes, I don't think it's possible to choose a bad pipe for these bikes, as the stock pipe just isn't very good to begin with, and how ktm packs their own silencers isn't very efficient either, and leaves a lot of channels in the silencer packing, due to the use of a pad of insulation, kinda like a fibreglass pillow lol, and when it forms around the perforated core, it gets folds that travel the length of the silencer body, an that tiny fold, allows the exhaust pulse to travel up and into these kinda "fissures" or cracks, voids, whatever word to best describe a long cavity, for the pressure wave to dissipate to, robbing the pressure as reducing overal flow as too much of the exhaust gases are get trapped inside the silencer, packing silencers is a bit of a dark art, learning what density to pack silencer insulation to can change power characteristics in tiny ways, but I usually tend to pack tighter than not, if may produce a bit more noise. But it produces better flow, lighter packed silencers will absorb more of the pressure wave reducing the exhaust gas velocity and pressure, softening up the delivery. So how you pack can affect things to a tiny degree, but it's getting super anal trying to squeeze every last percent out of you engine.

i am curious as well about what ignition timing you prefer, as one degree one way or the other plays a major role in power delivery as well, but NEVER EVER go past 3degees either way Past TDC, your engine will grenade, but even a 2 degree change either way is an incredible difference in how the engine responds, and it's totally backwards from how 4 stroke timing works, 4 strokes you advance the timing for more top end power, and retarding ignition timing will do the opposite and add a bit of bottom end delivery, where as 2 strokes are total opposite, advancing builds cylinder pressures and increases piston load resulting hotter cylinder temps, good for snappy throttle from idle up, helps keep the cylinder hot and responsive in the low end, and makes the power come on with more agression, retarding will keep the pipe hotter and therefore will increase the exhaust pulse wave return, and build up less cylinder pressures and takes advantage of the piston being past tdc to make it turn over faster, and easier, it also reduces cylinder temps and lowers load on the on the piston as well, and as for power delivery, it broadens out and smooths out the hit, and makes for plusher longer power delivery, but won't respond off the low end as well as an advanced ignition timing.

I'm a bit baffled by some peoples hesitance to trying something else, or make a change to their bike thinking it will ruin the way it feels, off-road motorcycles in this day in age are so adjustable in stock trim, you should be able to work with stock components and aligning specs to work with each other in unison. You can throw all the advanced aftermarket parts you want at a bike, and end up with something that doesn't work well just because the time and care wasn't taken to make everything work together properly. My mentality used to be make as much top end as possible because that's how your gonna beat a 4 stroke around the track, WRONG!!!! Now my focus is in the bottom half of the curve as that's where races are won, torque and the ability to gwt back up to speed quickly, by having a faster average speed, cornering prowess will always win out over strait line capability, most 2 strokes make Ample enough hp numbers for their weight, but they lack the low end delivery and torque to really be competive with today's 4 strokes, but I'm
Hoping that fi 2 strokes will make a big comeback, as fi 2 strokes whatever market they have entered, have dominated their fields, better fuel efficency, better power to weight, and where 2 strokes will gain the most, will be the bottom end, I really can't wait to see what a 150sx-tpi will do when it comes to power delivery against 250f's we could be looking at the equalizer and the eventual advantage to 2 strokes again, but that's just a hope and a pipe dream

https://m.youtube.com/watch?v=tNAtmKzqo9A

Even if you had a 500cc fi 4 stroke, this just proves how dominant fi 2 strokes could be, as this monster of a bike is making 70hp with a stock cr500 engine with a fi kit developed for it, no 450 on the stock level with the addition of fuel injection could possibly thing of making 70hp, and just think of what it would be like if they ported it? 75-80hp???? Like that's nuts, the service honda cr500 makes 90hp with a carb. When it comes to comparing cc to cc, 2'strokes will always have the advantage, but albeit the silly rules allowing such a displacement advantage, that's crap, your 4 stroke needs twice the displacement of a 125 to beat it, and next to double the displacement to beat a 250 2 stroke, so who's faster? Laws of AMA ruling still apply to the laws of physics, and the physics of the 2 stroke engine are beyond what a 4 strokes complexity could ever achieve, the fact a 2 stroke runs is a marvel of technology, 4 strokes premisnis basic at best. And If anyone thinks a 4 stroke mx bike is truely a technological wonder, that's so far from the truth, evening 88 Chevy 1 ton pickup with a smallblock 350 came with throttle body ignition lol, there's nothing new about 4 stroke tech, it's all recycled from the auto industry,

I have my ignition timing set just as it is from the factory and I haven’t even looked how to adjust ignition timing. Is there some ignition timing adjustment limits (screws with ”slots” to adjust ignition timing within certain range)?

I’m glad I get soon rid of my stock FMF exhaust pipe and silencer. You have explained very well how important a well packed silencer is for exhaust back pressure.

Fuel injection is nice and has many advantages but I will use that Keihin PWK 38S carb forever as I like the fact I can tune it myself and I also like all mechanical stuff. I trust more to carbs than FI and I’m not in a need of some pricey software updates etc. When carb tuning is done well I’m happy 😊. Factory FI is all about emissions and some of the bikes run really crappy. But they get many software updates and get better and better by the time. FI for adding performance and fast throttle response is anyway interesting and definitely if software maps are done correctly FI has power and driveability improvements over carb ones. Anyway good carb tuning is better than bad FI software map.

I totally agree that the fast throttle response and low/mid torque and power are more important than top end power as in mx it is almost always acceleration and not constant long high rpm if there is not very long straight sections. Usually not and even then like you wrote to have faster average speed is what matters and how fast you get out of the corners.

When going to crazy high hp numbers (70-90!) the problem is that it gets very tiring for the rider. There really is a limit how much power/weight a rider can stand for (at least I have a limit so my goal is to broaden up the powerband and not increase the topend power very much). You have given me many good tips. When I was a kid I had a Kawasaki KX 80 1989. It had adjustable ignition timing by turning the bottom part of the ignition (advancing or retarding the timing). If this TE250 has the same kind of ignition timing adjustment it is easy to test later how it will affect the performance when everything else is done first. But I will remember not to turn it too much so only some fine tuning for ignition timing then.

Oh Yeah man, it's located in the ignition cover, three 8mm bolts to move the stator plate forward for regarding, and back for advancing, and there is a timing mark to
Go off of, and be very conservative with adjustments, 1 degree one way or the other is a big change. I tend to run my ignition timing retarded at least a degree, if not 1.5-2 depending on conditions, as it smoothes out the hit, and lengthens power for 250 2 strokes as they are extremely snappy in power delivery even in stock trim, so I find it pays dividends in overal power delivery, but for the bush, the extra bottom end snap with a weighted crank can sometimes help out huge in tighter conditions where maybe half the rpm range is made useful, it also helps to ride a gear higher as off idle performance will be stronger, and comes on pipe with more agression, but it also makes the power taper off sooner in the rpm range, excellent for tight woods riding where obsticles come up quickly out of corners, and tight technical hill climbs, where on off throttle situations can be tricky.

And as for that yzr500, it must be a total handful, it looks like the guy wasn't even getting into the total top end of the machine, but what a sound!!!!! It sounds just insanely crisp, and very very similar to the new tpi ktm's but as far as carbs go, I agree, entirely self tuneable with the right brass and metering rods, simplistic and light weight, no fuel pump or electronics to deals with, just manipulation of tunnel velocities until they do their research and start to get mor aggressive with tuning the ecu'a for the fuel injection, then we will start to see some improvements and really show what a fi 2 stroke can do, but it's also kinda bothering me that it's just been the enduros models, and the difference between the enduro line porting and mx porting, would
Be radically different, taller port heights, tighter ratio trans, and higher compression heads to make the powerband more pipey.

I gotta ask, where abouts do you hail from? I'm living on Vancouver island bc, just a boat ride and hour drive from the place ktm went to tested their tpi 250 when it first was released, ridden by the man himself, graem Jarvis, in whistler bc. its nice to connect with people from all over and exchange stories and experiences, helps to inspire each other

I do plan on getting a motorcycle dyno, so I can start to test and prove legitimate results with anything I can get my hands on, and my dream would be to open up myown speed shop eventually, as a few of the bikes Iv put together and sold off have become local terrors at the tracks on the island. Goals and aspirations,

I’m from southern Finland. From the small country who just won Ice hockey World Championship... as you are from Canada you have to already know this... 😉

You seem to be a guy who knows how to set up these bikes to really fly on the track! Also you are so interested in tuning these bikes so it would be great if you get a own dyno and some day get your own shop.

By cylinder porting you must mean when they get modified by porting enduro vs. mx? In standard form both TC250 and TE250 also SX250 and EXC250 have same cylinder/ports. Only the cylinderhead and cdi box is different between enduro and mx versions. Same exhaust pipe but different silencer. All came with 36 mm carb. I don’t know if this is true on newer models but in 2015 models this is true.

FINLAND!!!!!!!!! FINLAND!!!!!!!!!! Please tell me you love metal and listen to kalmah, and as far as hockey goes, Canadian hockey is for bruisers, beat your opponents by beating them up, hockey over there that's talent, and a fair game, none of this, crap of, "well, that guy can out skate me, out handle me, and out score me...... I'll just wait till he goes for the puck and then nail him to the boards to get the puck" lol, it's brutal, not much skill, and the Vancouver Canucks are a bunch of choke shows who want to work on their golf swing rather than win the Stanley cup. European hockey is where the skill is at, and it shows.

kanadalainen jääkiekko on amerikkalaisille teehee! Hope it the translation was right!


I always thought that the sx porting was different that the enduro porting, as my friend ordered a 300sx kit for his 2013 250sx, but maybe it was just a different
combustion chamber displacement. That would be neat if that's what they did though, as it would make getting a 300xcw engine more appealing to me, Iv got this straaaaaange obsession with engine dimensions, and how different bore's and strokes work together, my madness knows no bounds when it comes to imagining different configurations and how they would work. Eventually I do plan to turn my tc144 into a square bore engine with a 58mm piston from a new gen 150sx, It would bump it up to a 154cc engine, but the ultimate engine in my mind would be to turn it into a tc200, and cap off 6th gear to make it a 5 speed, I'd be in heaven, Iv ridden a 200 before, and for how light it was, it made ridiculous power, and Iv read articles about guys fully race prepping the ktm 200 sx engine to pump out close to 54-55hp at the wheel, that's an incredible amount of power for a 189cc 2 stroke, mind you it was a racegas only build, but I figure If I could get close to 50hp out of a 200, it would be more than enough power for me to ride happily the rest of my life.

And all of the ktm 250/300's from 2004-2016, came with the pwk 36, honestly they messed up, they needed to swap carbs from the 125 and the 250, the jets were almost perfect when I ordered my pwk36s for my 2016 125sx, even the 6.5mm carburetor slide is more suited for the 125 than the 250, and visa versa, the pwk38 in the 125 comes with the 7mm carb slide, its really strange why they did it in this way. But both carb configurations are better suited to the other bike, it makes no sense, why have a richer carb slide with a smaller carb bore, on a bike with twice the displacement!??! if anyone has a 125 ktm or a 250 ktm, they should swap carbs, they will both be happy with the results lol.

Nice to hear from you again männänpää!

Here's my 08 144, Iv owned the engine cases in that bike since 2009 and my first yz250

Nice bike and jumps! Yes I listen to rock music like Motörhead etc. I also like good punk music. Thanks for your kind words regarding European Ice Hockey! Your translation is good =).

Yes the only difference in TC/TE/SX/EXC 250 is the cylinderhead. Cylinder itself and piston is the same. 250 vs. 300 are different obviously.

When I bought my Keihin PWK 38S as new it had 6.5 slide. In my European version of TE250 original carb Keihin PWK36 S had number 7 slide. I was a bit surprised as I thought there should have been 6.5 in it and 7 in 38 mm, but it was just opposite. Slide 7 is leaner so I will continue to use 6.5 slide as with my current jetting it doesn´t feel too rich and throttle response is crispy. Do you recommend me to try number 7 slide in my 250 with NECJ 3rd clip, AS 2 open, 175 main jet, 42 pilot jet?

If no ill results are present, I'd say leave it, if your not getting any spooge out the silencer, then your golden! Excessive premix out the silencer is usually too Rich of a pilot jet, but if your getting away with the 6.5 slide keep it, the leaner slide will take away a tiny bit of response, I like a richer carb slide personally, it helps with low end throttle
Response, I have a 5.5mm slide in my 144, and it's really perky off idle, but i need to sleep, its late here.... early there

hyvää yötä ja hyvää huomenta

I installed RK-Tek head and Wiseco Racers Elite 1 ring piston, but there is still original FMF factory TE 250 exhaust. Jetting at the moment 178 main jet, 45 pilot jet, NEDJ 3rd clip (half clip richer than NECJ 3rd), AS 2 turns open. Red power valve auxiliary spring (soft) and 1.8 mm coil wire diameter softer power valve main spring. I polished cylinder exhaust ports and power valve flap and aligned the cylinder exhaust flange to the cylinder exhaust port. Transfer ports got just some finishing work and I did not polish them so the gasoline and air will mix better. Just rough enough surface and no changes to port shapes or port windows. I set my power valve flap height (Z dimension) to 48.0 mm (std). I had to use quite thick cylinder base gasket combo with Wiseco Racers Elite piston to get X dimension (deck height) to 0.0 mm. I used 0.5 mm and 0.4 mm gaskets = 0.9 mm. Now transfer ports open fully at BDC and main exhaust port opens almost fully too. So extended exhaust and transfer ports duration with this raised cylinder. Piston to head clearance is 1.00 mm. I did just a bit of break in for the new piston yesterday with 32:1 mix. I will use this 32:1 for now on for better lubrication and ring seal. As combustion is faster with RK-Tek head I decided to change back my TE 250 CDI with less aggressive/advanced ignition timing. I took off TC/SX 250 CDI this evening so it was just used for around 30 minutes. It had no pinging/detonation with low/mid revs but I want more top end power and over rev so I changed that TE 250 CDI back as I have understood this RK-Tek head have been designed more for less ignition advance. It should perform this way even better. I am still waiting for Bill’s Pipes exhaust... this time Works pipe as to get a Nickel coated version takes forever... It has been in back order from Slavens Racing from 21st March...

RK-Tek head has awesome low and mid range power/torque! Money well spent =) . Smooth and strong power. Top end power will be tested a bit later when new piston has a bit more break in done.

Well, it's been a while, sorry for the delayed response, busy with my house build, and work, and completely forgot about this. That's great news your stoked with how it's performing, Iv been putting in time getting my jetting sorted out, but haven't ridden in a while. I will say that my bike needs work, pretty sure the reeds are done, and my cylinder is long overdue for a nikasil coating, so I plan to tear it down and get the work done to make it reliable again, but when that will happen I don't know. Planning on porting it more when it's out before I send it out for a do-over. I'll take some pictures of before and after once I get it around to it, if I ever do hahahahahaha. House has been hectic lately, with putting the service in at my property, and framing about to begin in a few weeks, but I'm planning a bit of a "work party" for my track, just to beat the bush down, im gonna get my friends to bring their 4x4's over to just go drive around in the area that I'm gonna use for the track and see if they can carve in a bit of a loop with their trucks before I get an excavator out there to break
Ground and make the track happen.

But back to bikes, I picked up a scored 125 cylinder I'm porting on the side before I send it out for a bore job, and install a new generation 2016+ 150sx piston, so I'll make my engine a square bore 154cc engine.

Also, a friend of mind is asking if I want to buy his 2013 husaberg 300, and I really want to, I'd love a dedicated trail bike, so I don't have to worry about mangling a scalvini pipe on a tree or something. But that seems like a good Time to me, I miss trail riding, and a trail bike would take a bit of the worry out of messing up my track queen hahahahahah, but it would be nice to throw a leg over a dedicated trail bike for once, I'm so used to riding mx bikes on trails itle nice to have a playful off-road powerband for a change, and I will for sure be modding it to my liking if I do get it which I'm hoping I can. It's been a bit since last post, and I'm sure you have a lot of riding in and more tuning done to suite your tastes, so I'm looking forward to reading about it, taker easy!