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250sx powerband


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Hi harohunter,

All 250 two strokes have more low end and more overall power then your CR125 so I wouldn't worry about your experience with the 125 or let it influence any 250 opinions about JAP or KTM 250's. All 125's are more of a light switch then any production 250. I like the 250 in general for overall power and low end. I always have. It depends on what type riding you will be doing, your size, and riding style.

I haven't' ridden the 07 so any comparisons are to my '03 and are based on what someone else said, complained about, or a review on the '07 or other newer bikes. So, maybe someone that has ridden them all will contest or add to what I say. With that in mind and to put my '03 in perspective for comparison to the '07, the 03 is supposed to have the most radical, hard to ride power band of the KTM 250's. All the newer 250SX's have smoother power bands then mine, at the expense of a little bit of top end power, but they all still have more power then any of the Jap bikes I believe. The CR250 is supposed to have a smoother power band and less power then the KTM I have heard (it is hit and miss, with the '01 CR250 being the best engine and '02 being a problem). The KTM's still tend to have more low end torque. The Jap 2 strokes stopped development for the most part in around '2000 or a little before and of course some stopped production all together shortly after that. The ones that stayed with 2 strokes still tweaked a few things here and there but focused there efforts on the 4 strokes. Yamaha's are not known to have the most power but a very linear and ride-ably power band. KTM's are known to have great power (better power) and still have more low end. That is one reason why so many are ridden in the woods. That and the stock suspension sucks on the track for the older ones. I don't know how many times I have heard "I wish I had your engine on my bike". The Yamaha suspension is very nice stock. Since then I have had my suspension reworked and it is much better. The KTM might not be any less linear then the Yamaha YZ250 but it probably feels like it since it has a little more power. The reed case induction works great on the KTM's. I don't hear any complaints on either bikes power in the woods or on the track except when compared to 450's on the track. In the tight woods there is no comparison, the two strokes are all better.

Even my '03 I wouldn't say was a light switch. Even before modification it had good low end power, surprisingly good for a MX 2 stroke. It just had a tremendous explosion of power in the mid range that made it hard to ride. After some modification it now has more low end then the enduro models have stock and more high end then it had stock. The power band is very smooth IMO . It is now a great woods bike and still fun to ride on the track.

On top of all that KTM's are easier to modify then JAP bikes. You don't have to be a tuner, or maybe I should say you can easily become a tuner. You can tweak and modify things to move, and change the power band on any of the SX's (or other models for that matter) to what ever you want it to be. You can do this by adding power in areas of the curve that are weak to smooth the curve and or by shifting it from peak areas to low areas. Even the '03 had a lot of room to move things around and to increase overall performance across the power band. The stock head design and pipe leave a lot of room for improvement on all models and there are a lot of folks that know how to work these issues here and on KTM Talk. Some of the things you can change are free and some cost money.

A list of things that change the way power is delivered and how they affected my '03 250SX.

  • Flywheel weight: The SX especially when modified has so much power it needs some more weight IMO. It doesn't detract from acceleration IMO. It just makes the delivery a little smoother. Very subtle difference. It makes it a little easier to maintain traction on a MX track in hard dusty slippery conditions, helps prevent stalling at low RPM when working near idle and feathering the clutch, and is just all around good. Since you are starting with a very light flywheel/crankshaft on the SX you have the option to go from there all the way to the equivalent of the enduro models. If you don't like it in some particular situation you can take it off.
  • Pipes: Many options for exhaust changing the power band focusing on low end high end and some that do a better job over all. The SST I am running seems to do a great job overall.
  • Jetting: KTM's are almost always too rich in all circuits. The chart in my manual is way off. They are about 10 points too rich on the high and low end recommendations or stock jetting. Adjusting your pilot and needle can add a buch of low end power and tweak it to your riding style and preference. You can make it more responsive or soften the throttle response in different areas of throttle.
  • Compression and cylinder head shape: There is a lot of room for improvement here. More so on the endure models but even on the SX's. KTM and most other manufactures designed their heads and set compression to run on some piss poor fuel. You can get more low end power and more all the way through most of the power band with a cut down and reshaped head. Even when starting from the SX head. You can experiment with this just by reducing cylinder base gaskets and get the increased compression and also change port timing slightly from more low end. Having the head reworked will have larger benefits.
  • Port timing can be advanced and retarded for more low or high end power by changing cylinder base gaskets as mentioned above.
  • Power Valve modification: You can tweak the low position (Z dimension) of the power valve flapper for more low end torque, with no trade off in high end power. This may require some clearing work to the power valve to avoid contact with the piston.
  • Power Valve Springs: Change how soon power valves open. You can mellow the delivery if you want.
  • CDI: The SX CDI is the most aggressive of the various models. Usually a modification is to move from one of the enduro models to the SX one. The SX CDI is not bad for low end either.
  • Reed Valve: You can change reed pedals or entire reed valve assemblies for various power delivery effects.

If all that doesn't get what you want you can put a 300SX top end on it (I think it works for that year?).

Hope that helps

Elaborate a little more on what you want to do.

What type riding do you want to do? MX, hare scrambles, woods racing, trail riding, both, all, etc?

What size are you, weight, height?

What level rider do you think you are, or how aggressive do you ride or want to ride?

Edited by Gary jp4
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Hi harohunter,

All 250 two strokes have more low end and more overall power then your CR125 so I wouldn't worry about your experience with the 125 or let it influence any 250 opinions about JAP or KTM 250's. All 125's are more of a light switch then any production 250. I like the 250 in general for overall power and low end. I always have. It depends on what type riding you will be doing, your size, and riding style.

I haven't' ridden the 07 so any comparisons are to my '03 and are based on what someone else said, complained about, or a review on the '07 or other newer bikes. So, maybe someone that has ridden them all will contest or add to what I say. With that in mind and to put my '03 in perspective for comparison to the '07, the 03 is supposed to have the most radical, hard to ride power band of the KTM 250's. All the newer 250SX's have smoother power bands then mine, at the expense of a little bit of top end power, but they all still have more power then any of the Jap bikes I believe. The CR250 is supposed to have a smoother power band and less power then the KTM I have heard (it is hit and miss, with the '01 CR250 being the best engine and '02 being a problem). The KTM's still tend to have more low end torque. The Jap 2 strokes stopped development for the most part in around '2000 or a little before and of course some stopped production all together shortly after that. The ones that stayed with 2 strokes still tweaked a few things here and there but focused there efforts on the 4 strokes. Yamaha's are not known to have the most power but a very linear and ride-ably power band. KTM's are known to have great power (better power) and still have more low end. That is one reason why so many are ridden in the woods. That and the stock suspension sucks on the track for the older ones. I don't know how many times I have heard "I wish I had your engine on my bike". The Yamaha suspension is very nice stock. Since then I have had my suspension reworked and it is much better. The KTM might not be any less linear then the Yamaha YZ250 but it probably feels like it since it has a little more power. The reed case induction works great on the KTM's. I don't hear any complaints on either bikes power in the woods or on the track except when compared to 450's on the track. In the tight woods there is no comparison, the two strokes are all better.

Even my '03 I wouldn't say was a light switch. Even before modification it had good low end power, surprisingly good for a MX 2 stroke. It just had a tremendous explosion of power in the mid range that made it hard to ride. After some modification it now has more low end then the enduro models have stock and more high end then it had stock. The power band is very smooth IMO . It is now a great woods bike and still fun to ride on the track.

On top of all that KTM's are easier to modify then JAP bikes. You don't have to be a tuner, or maybe I should say you can easily become a tuner. You can tweak and modify things to move, and change the power band on any of the SX's (or other models for that matter) to what ever you want it to be. You can do this by adding power in areas of the curve that are weak to smooth the curve and or by shifting it from peak areas to low areas. Even the '03 had a lot of room to move things around and to increase overall performance across the power band. The stock head design and pipe leave a lot of room for improvement on all models and there are a lot of folks that know how to work these issues here and on KTM Talk. Some of the things you can change are free and some cost money.

A list of things that change the way power is delivered and how they affected my '03 250SX.

  • Flywheel weight: The SX especially when modified has so much power it needs some more weight IMO. It doesn't detract from acceleration IMO. It just makes the delivery a little smoother. Very subtle difference. It makes it a little easier to maintain traction on a MX track in hard dusty slippery conditions, helps prevent stalling at low RPM when working near idle and feathering the clutch, and is just all around good. Since you are starting with a very light flywheel/crankshaft on the SX you have the option to go from there all the way to the equivalent of the enduro models. If you don't like it in some particular situation you can take it off.
  • Pipes: Many options for exhaust changing the power band focusing on low end high end and some that do a better job over all. The SST I am running seems to do a great job overall.
  • Jetting: KTM's are almost always too rich in all circuits. The chart in my manual is way off. They are about 10 points too rich on the high and low end recommendations or stock jetting. Adjusting your pilot and needle can add a buch of low end power and tweak it to your riding style and preference. You can make it more responsive or soften the throttle response in different areas of throttle.
  • Compression and cylinder head shape: There is a lot of room for improvement here. More so on the endure models but even on the SX's. KTM and most other manufactures designed their heads and set compression to run on some piss poor fuel. You can get more low end power and more all the way through most of the power band with a cut down and reshaped head. Even when starting from the SX head. You can experiment with this just by reducing cylinder base gaskets and get the increased compression and also change port timing slightly from more low end. Having the head reworked will have larger benefits.
  • Port timing can be advanced and retarded for more low or high end power by changing cylinder base gaskets as mentioned above.
  • Power Valve modification: You can tweak the low position (Z dimension) of the power valve flapper for more low end torque, with no trade off in high end power. This may require some clearing work to the power valve to avoid contact with the piston.
  • Power Valve Springs: Change how soon power valves open. You can mellow the delivery if you want.
  • CDI: The SX CDI is the most aggressive of the various models. Usually a modification is to move from one of the enduro models to the SX one. The SX CDI is not bad for low end either.
  • Reed Valve: You can change reed pedals or entire reed valve assemblies for various power delivery effects.

If all that doesn't get what you want you can put a 300SX top end on it (I think it works for that year?).

Hope that helps

Elaborate a little more onto what you want to do.

What type riding do you want to do? MX, hare scrambles, woods racing, trail riding, both, all, etc?

What size are you, weight, height?

What level rider do you think you are, or how aggressive do you ride or want to ride?

I want do a little bit of every type of riding, except dunes there's no dunes here. E I will be doing some mx just for fun. I may do some hare scrambles they look really fun.

I am 5'9 165lbs, I'd say beginner to intermediate level. I have a 125 and a crf250. Ive ridden some 450s and can handle it just feels like a handful but I could probably handle it. The 250sx looks like a good choice because it's 30 lbs lighter and feels lighter. But I'd love to have a 07+ 450 with estart:ride:. All my friends have 450s and all we have is flat open areas and I'm tired of ringing out my small bores trying to keep up on the open areas.

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Out of the box a 07 250SX is a light switch, it RIPS but it's no XC. It can be made more linear by changing the powervalve spring and dropping a couple teeth off the rear sprocket.

I had a 07 250SX, that I just couldn't come to terms with, I was trying to offroad it but the motor and suspension didn't have that in mind. I have a few friends with 250XC's that swapped bikes with me on the trail and they couldn't get theres back quick enough because my SX was "too much", mind you their XC's felt like they had a plugged exhaust to me. I had the SX pretty well set up too; revalved the suspension(twice), resprung, G2 throttle cam, green spring, PC platinum 2 and spark arrestor, scotts damper, clockwork tank, and smaller sprocket in back. I think if I would have put on some open chamber forks on the SX I would have ended up keeping it.

I still have a old 06 YZ 250 and it's much more linear and better offroad out of the box then that 07 SX was IMO.

With that said the SX may be a handful for you unless your will to spend some time on set up.

What about a 200?

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I have an 08 250SX and I think it is just right. With the red PV spring and aggressive ignition, it is a light switch. I you change the PV spring and the ignition it is much more tame. However, I ride in mostly open terrain so a delicate throttle hand is not as critical here as some other places. Also, I weight 250lbs, so I'm sure my weight mellows out the power quite a bit. For reference only, I am a mid pack finisher in the open expert desert class.

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