2019 125SX High Compression Head or Get KTM 150 kit

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5/16/2020 11:24 AM

Hi All,
I have searched and can't find my specific answer. So don't kill me if it's in here. I have a 2019 KTM 125SX that I got a few months ago. Absolutely love this little bike, so light. Not too much power. Bought it for my son but he doesn't want it. I let him have my 2016 350SXF. I also have an '18 450SXF that I bought for MX. I do mostly offroad racing in north Texas which is pretty wide open. Very little slow technical but we do get into the woods. I set up my 350SXF as my woods racer and did double duty when I did Vet MX. Was getting beat on the 350 (too lazy to shift) so I got the 450. Only had a couple of rides on the 450 and I am only a little faster on it. I am thinking of converting the 125 to an offroad racer for our tighter woods tracks. My question comes down to would a high compression head and maybe pipe/silencer increase the power equivalent to the KTM 150 kit? Wonder if anyone has done that and can answer. I know I will be giving up some torque down low but you gotta scream the 125 anyway. I have only had a few chances to ride with my friends in the woods and on the track. Seems like I am just a tad slower on the 125 but man when it comes to tight corners, whew what fun. Also, I am jumping more easily as this bike feels like I can do almost anything and not get too out of control. I don't have the same feeling on the 450.

Thoughts?

Anyone put an XC tank on a '19SX? The body is different for 19 but I know it can be done for 16-18.

Many thanks

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5/16/2020 1:49 PM

The short answer is that the high compression 125 will feel pipey and require more aggression. It will not be as powerful as a stock 150. The 150 will not be as hyper but will have more torque. You could always high-comp the 150 later too. I'd vote for the 150 kit unless you are doing it inexpensively.

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Braaapin' aint easy.

5/16/2020 2:08 PM

Very interesting! I literally was just in the same boat as you and converted my 2016 125SX to 150XC. All in with rebuilding and powder it was about $2,000. So you need to consider that, is it worth that or just sell the 125 for a 250XC?

I ended up dropping in because I have so many part for the bike. When I got it done, I only street tested the 150 and it’s got wayyy more juice than my 125 that was ported + VHM high comp head. My 125 was really good and would scream up top but tough to ride is tight situations.

To convert the bike, I did a OEM 150 kit with the RK Tech high comp head insert. 9oz flywheel weight, 18in rear wheel and XC tank. basically the only difference I have from stock XC is the transmission ratio. But I went up a tooth in the rear to help lug in tight spots. I’m also working with different power valve springs to see which is best.

I’m going to trail text next week and can give you a better comparison.

This is when I had it set up for track riding but was using it offroad (Not sure why all the photos load sideways now)
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Rebuilding here:
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5/16/2020 2:48 PM

Good info Joe, seems like the 150 is the best option. I've heard the 150 doesn't rev out like the 125 but in the woods may not matter. Nice looking bike.

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5/16/2020 4:44 PM

GranburyChuck wrote:

Good info Joe, seems like the 150 is the best option. I've heard the 150 doesn't rev out like the 125 but in the woods may not matter. Nice looking bike.

I’ve heard that a lot as well and I can give you more details next week. But when I did a quick test on the street the bike pulled way harder and longer than I thought. Granted on the pavement all bikes feel like monsters.

The small bores will never lug like a 300 but this set up is pretty impressive so far!

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5/16/2020 8:32 PM

GranburyChuck wrote:

Hi All,
I have searched and can't find my specific answer. So don't kill me if it's in here. I have a 2019 KTM 125SX that I got a few months ago. Absolutely love this little bike, so light. Not too much power. Bought it for my son but he doesn't want it. I let him have my 2016 350SXF. I also have an '18 450SXF that I bought for MX. I do mostly offroad racing in north Texas which is pretty wide open. Very little slow technical but we do get into the woods. I set up my 350SXF as my woods racer and did double duty when I did Vet MX. Was getting beat on the 350 (too lazy to shift) so I got the 450. Only had a couple of rides on the 450 and I am only a little faster on it. I am thinking of converting the 125 to an offroad racer for our tighter woods tracks. My question comes down to would a high compression head and maybe pipe/silencer increase the power equivalent to the KTM 150 kit? Wonder if anyone has done that and can answer. I know I will be giving up some torque down low but you gotta scream the 125 anyway. I have only had a few chances to ride with my friends in the woods and on the track. Seems like I am just a tad slower on the 125 but man when it comes to tight corners, whew what fun. Also, I am jumping more easily as this bike feels like I can do almost anything and not get too out of control. I don't have the same feeling on the 450.

Thoughts?

Anyone put an XC tank on a '19SX? The body is different for 19 but I know it can be done for 16-18.

Many thanks

Built a 2019 XC 150 from a 2019 SX 150, a 2019 XC 250 tank fits perfect.You will need a different gas cap for the XC tank.

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5/16/2020 8:57 PM

GranburyChuck wrote:

Hi All,
I have searched and can't find my specific answer. So don't kill me if it's in here. I have a 2019 KTM 125SX that I got a few months ago. Absolutely love this little bike, so light. Not too much power. Bought it for my son but he doesn't want it. I let him have my 2016 350SXF. I also have an '18 450SXF that I bought for MX. I do mostly offroad racing in north Texas which is pretty wide open. Very little slow technical but we do get into the woods. I set up my 350SXF as my woods racer and did double duty when I did Vet MX. Was getting beat on the 350 (too lazy to shift) so I got the 450. Only had a couple of rides on the 450 and I am only a little faster on it. I am thinking of converting the 125 to an offroad racer for our tighter woods tracks. My question comes down to would a high compression head and maybe pipe/silencer increase the power equivalent to the KTM 150 kit? Wonder if anyone has done that and can answer. I know I will be giving up some torque down low but you gotta scream the 125 anyway. I have only had a few chances to ride with my friends in the woods and on the track. Seems like I am just a tad slower on the 125 but man when it comes to tight corners, whew what fun. Also, I am jumping more easily as this bike feels like I can do almost anything and not get too out of control. I don't have the same feeling on the 450.

Thoughts?

Anyone put an XC tank on a '19SX? The body is different for 19 but I know it can be done for 16-18.

Many thanks

XC706 wrote:

Built a 2019 XC 150 from a 2019 SX 150, a 2019 XC 250 tank fits perfect.You will need a different gas cap for the XC tank.

How did you like it offroad? Did you add a fly wheel weight?

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5/16/2020 9:26 PM

GranburyChuck wrote:

Hi All,
I have searched and can't find my specific answer. So don't kill me if it's in here. I have a 2019 KTM 125SX that I got a few months ago. Absolutely love this little bike, so light. Not too much power. Bought it for my son but he doesn't want it. I let him have my 2016 350SXF. I also have an '18 450SXF that I bought for MX. I do mostly offroad racing in north Texas which is pretty wide open. Very little slow technical but we do get into the woods. I set up my 350SXF as my woods racer and did double duty when I did Vet MX. Was getting beat on the 350 (too lazy to shift) so I got the 450. Only had a couple of rides on the 450 and I am only a little faster on it. I am thinking of converting the 125 to an offroad racer for our tighter woods tracks. My question comes down to would a high compression head and maybe pipe/silencer increase the power equivalent to the KTM 150 kit? Wonder if anyone has done that and can answer. I know I will be giving up some torque down low but you gotta scream the 125 anyway. I have only had a few chances to ride with my friends in the woods and on the track. Seems like I am just a tad slower on the 125 but man when it comes to tight corners, whew what fun. Also, I am jumping more easily as this bike feels like I can do almost anything and not get too out of control. I don't have the same feeling on the 450.

Thoughts?

Anyone put an XC tank on a '19SX? The body is different for 19 but I know it can be done for 16-18.

Many thanks

XC706 wrote:

Built a 2019 XC 150 from a 2019 SX 150, a 2019 XC 250 tank fits perfect.You will need a different gas cap for the XC tank.

CarlinoJoeVideo wrote:

How did you like it offroad? Did you add a fly wheel weight?

No flywheel weight but I built this for my son who is racing Pro XC/HS. We have the bike working very well offroad, Bud carbon muffler, raised compression, blue PV spring, JD jet block kit, Jarvis mods, 5.25 slide, JD needle, opened up the air box. He likes the stock 13/48 gearing, but if I was racing it offroad ( +50A ) I would add a tooth or two to the rear sprocket.Running a 18' rear wheel.

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5/17/2020 5:01 AM

XC706 can you speak to the Jarvis mods you did? I drilled the holes in the drain bolt. Have on order the jet block gasket kit. I didn't bother with the JD Jetting kit yet as I just found the jet block gasket issue. Wanted to try it and see how good it is. Did you file the slide?

I am probably no where near your skill level. I race Over 52 Amateur offroad, sometimes Over 45 to race with friends. I will have the opportunity to race it stock in a couple of weeks, hopefully. Our first race back was rained out yesterday, bummer.

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5/17/2020 7:08 AM

Also, XC706, did you have to get new plastics when you put the XC tank on or did the SX ones fit?

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5/17/2020 8:21 AM

Hey Chuck, no new plastic or seat for the XC tank, bolts right on other than the gas cap and a shorter fuel line.
I did all the Jarvis mods - drain bolt holes, drilled out baffle holes, crimped over flow tube and filed slide. We are at elevation 4000 - 7000 ft. The Mikuni at elevation on the 150 is a very finicky carb. On the days its running well I believe it makes more power than the Keihin ( which we have run a 36mm ) if you want a set it and forget carb just put a Keihin on it.

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5/17/2020 8:43 AM

GranburyChuck wrote:

Also, XC706, did you have to get new plastics when you put the XC tank on or did the SX ones fit?

Tank fits with everything SX. The XC gas cap is different, my tank came with one, but double check. I used the exhausting fuel line, just cut it shorter.

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5/17/2020 9:52 AM

GranburyChuck wrote:

Also, XC706, did you have to get new plastics when you put the XC tank on or did the SX ones fit?

CarlinoJoeVideo wrote:

Tank fits with everything SX. The XC gas cap is different, my tank came with one, but double check. I used the exhausting fuel line, just cut it shorter.

When I ordered an oem xc tank, it came with petcock and cap. Recently ordered an acerbis and it only came with a cap

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5/17/2020 11:59 AM

GranburyChuck wrote:

Also, XC706, did you have to get new plastics when you put the XC tank on or did the SX ones fit?

CarlinoJoeVideo wrote:

Tank fits with everything SX. The XC gas cap is different, my tank came with one, but double check. I used the exhausting fuel line, just cut it shorter.

GoggleFiend904 wrote:

When I ordered an oem xc tank, it came with petcock and cap. Recently ordered an acerbis and it only came with a cap

For what year OEM?

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5/18/2020 5:28 PM

CarlinoJoeVideo wrote:

Tank fits with everything SX. The XC gas cap is different, my tank came with one, but double check. I used the exhausting fuel line, just cut it shorter.

GoggleFiend904 wrote:

When I ordered an oem xc tank, it came with petcock and cap. Recently ordered an acerbis and it only came with a cap

XC706 wrote:

For what year OEM?

14 250sx

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5/18/2020 6:10 PM

GoggleFiend904 wrote:

When I ordered an oem xc tank, it came with petcock and cap. Recently ordered an acerbis and it only came with a cap

XC706 wrote:

For what year OEM?

GoggleFiend904 wrote:

14 250sx

Wrong year. OP is asking about 2019 XC tanks. 2016 - 2018 come complete with gas cap, 2019 comes complete except for the gas cap. 2018 and earlier XC tanks do not fit on the 2019-20 SX 150.

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5/18/2020 6:21 PM

XC706 wrote:

For what year OEM?

GoggleFiend904 wrote:

14 250sx

XC706 wrote:

Wrong year. OP is asking about 2019 XC tanks. 2016 - 2018 come complete with gas cap, 2019 comes complete except for the gas cap. 2018 and earlier XC tanks do not fit on the 2019-20 SX 150.

Thank you for clarifying that. I had no idea they wouldn’t still come with the cap

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5/18/2020 9:54 PM

CarlinoJoeVideo wrote:

Very interesting! I literally was just in the same boat as you and converted my 2016 125SX to 150XC. All in with rebuilding and powder it was about $2,000. So you need to consider that, is it worth that or just sell the 125 for a 250XC?

I ended up dropping in because I have so many part for the bike. When I got it done, I only street tested the 150 and it’s got wayyy more juice than my 125 that was ported + VHM high comp head. My 125 was really good and would scream up top but tough to ride is tight situations.

To convert the bike, I did a OEM 150 kit with the RK Tech high comp head insert. 9oz flywheel weight, 18in rear wheel and XC tank. basically the only difference I have from stock XC is the transmission ratio. But I went up a tooth in the rear to help lug in tight spots. I’m also working with different power valve springs to see which is best.

I’m going to trail text next week and can give you a better comparison.

This is when I had it set up for track riding but was using it offroad (Not sure why all the photos load sideways now)
Photo
Photo

Rebuilding here:
Photo
Photo
Photo
Photo
Photo
Photo
Photo

What exhaust is that? I see the silencer is an Akrapovic, but what’s the expansion chamber? Any difference between that and the full FMF? I may have to spend some money that I don’t need to!

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5/18/2020 10:43 PM

I have a built 125 and a stock 150 that are both more moto geared and have raced both in a couple off-road championships. Our trails here are 60 percent open and 40 percent tight. I’ll take the 125 (even in stock form) over the 150 any day. The benefit of the top end the 125 gives you in the open sections trumps the bottom end you get from the 150, I find myself just having to be a hair more conscious of my gear selection and clutch work in the tight stuff with the 125.

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Unleaded tastes a little tangy. Supreme is kinda sour, and diesel tastes pretty good.

5/19/2020 7:32 AM

CarlinoJoeVideo wrote:

Very interesting! I literally was just in the same boat as you and converted my 2016 125SX to 150XC. All in with rebuilding and powder it was about $2,000. So you need to consider that, is it worth that or just sell the 125 for a 250XC?

I ended up dropping in because I have so many part for the bike. When I got it done, I only street tested the 150 and it’s got wayyy more juice than my 125 that was ported + VHM high comp head. My 125 was really good and would scream up top but tough to ride is tight situations.

To convert the bike, I did a OEM 150 kit with the RK Tech high comp head insert. 9oz flywheel weight, 18in rear wheel and XC tank. basically the only difference I have from stock XC is the transmission ratio. But I went up a tooth in the rear to help lug in tight spots. I’m also working with different power valve springs to see which is best.

I’m going to trail text next week and can give you a better comparison.

This is when I had it set up for track riding but was using it offroad (Not sure why all the photos load sideways now)
Photo
Photo

Rebuilding here:
Photo
Photo
Photo
Photo
Photo
Photo
Photo

T-Fish wrote:

What exhaust is that? I see the silencer is an Akrapovic, but what’s the expansion chamber? Any difference between that and the full FMF? I may have to spend some money that I don’t need to!

It’s the KTM Factory pipe. I never went back to back with the Fatty. They are shaped a bit different, I think you can split hairs on which one gives your more bottom or mid. I have my bike set up for as much bottom as I can, so it falls off a bit early with my power valve setting.

Sick looking pipe, for some reason not many people know about it.

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5/19/2020 2:39 PM

Save some money & throw a 38mm Keihin carb with STIC metering block in it. It does way more for torque curve & overall power than 150 kit or any other mod for that matter.............Pulls like a 250f......

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5/20/2020 6:31 AM

Tracktor, is there data to show that the carb change does improve the power? Currently considering a Smart Carb. Of course the claims seem a little far fetched. 10% power improvement. They sent a dyno chart for a YZ125 and it did show that improvement. However, when I compared the baseline to a dyno done by MXA for a 2018 the baseline was a little down on the Smart Carb dyno. Still the horsepower showed slightly higher than what MXA dyno had. Also, Smart Carb claims greater fuel efficiency. That is important for me because if true I wouldn't have to buy a larger tank for the bike. So in effect, the Smart Carb might give a little boost in power (probably not 10%) and increase efficiency thus the high cost $700, beats the cost of the KTM kit $800 + 200 (tank).

Anyone with experience like this please let me know

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5/20/2020 10:42 AM

GranburyChuck wrote:

Tracktor, is there data to show that the carb change does improve the power? Currently considering a Smart Carb. Of course the claims seem a little far fetched. 10% power improvement. They sent a dyno chart for a YZ125 and it did show that improvement. However, when I compared the baseline to a dyno done by MXA for a 2018 the baseline was a little down on the Smart Carb dyno. Still the horsepower showed slightly higher than what MXA dyno had. Also, Smart Carb claims greater fuel efficiency. That is important for me because if true I wouldn't have to buy a larger tank for the bike. So in effect, the Smart Carb might give a little boost in power (probably not 10%) and increase efficiency thus the high cost $700, beats the cost of the KTM kit $800 + 200 (tank).

Anyone with experience like this please let me know

Big thread on Thumpertalk where a guy (MOG) dynoed a bunch of STIC setups on a KTM 150. Ended up with similar power curve as a 250sxf. We run multiple bikes with them and I can tell you it's no joke. COmpletely changes the torque cruve. Every person who has tried one of our bikes with them loves it. BTW, any dyno charts need to be same day same dyno or basically useless for comparison. I haven't tried a Smart Carb personally so maybe they are great. That said I simply can't imagine more improvement than what we have gotten from running STIC's in our bikes. As for fuel useage I can't really comment as we ride MX and I haven't cared to monitor that............PS, even though I post a lot about them I have no relation to the company other than I truly believe in the product. I have ended up doing some testing/feedback for George simply because I am big on tuning but I have purchase 5 STICs myself. If you were in the NW I would let you test one of my extras before buying.

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5/20/2020 4:56 PM

The smart carb and lectern might be better suited to 250, 300 trail bike imo

I ran Smart on rm144, and lectron onnsx150 and prefer a regular carb.

Silencer is important on sx150, most aftermarket ones are slower because the outlet is too narrow

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5/21/2020 1:46 PM

GranburyChuck wrote:

Tracktor, is there data to show that the carb change does improve the power? Currently considering a Smart Carb. Of course the claims seem a little far fetched. 10% power improvement. They sent a dyno chart for a YZ125 and it did show that improvement. However, when I compared the baseline to a dyno done by MXA for a 2018 the baseline was a little down on the Smart Carb dyno. Still the horsepower showed slightly higher than what MXA dyno had. Also, Smart Carb claims greater fuel efficiency. That is important for me because if true I wouldn't have to buy a larger tank for the bike. So in effect, the Smart Carb might give a little boost in power (probably not 10%) and increase efficiency thus the high cost $700, beats the cost of the KTM kit $800 + 200 (tank).

Anyone with experience like this please let me know

Tracktor wrote:

Big thread on Thumpertalk where a guy (MOG) dynoed a bunch of STIC setups on a KTM 150. Ended up with similar power curve as a 250sxf. We run multiple bikes with them and I can tell you it's no joke. COmpletely changes the torque cruve. Every person who has tried one of our bikes with them loves it. BTW, any dyno charts need to be same day same dyno or basically useless for comparison. I haven't tried a Smart Carb personally so maybe they are great. That said I simply can't imagine more improvement than what we have gotten from running STIC's in our bikes. As for fuel useage I can't really comment as we ride MX and I haven't cared to monitor that............PS, even though I post a lot about them I have no relation to the company other than I truly believe in the product. I have ended up doing some testing/feedback for George simply because I am big on tuning but I have purchase 5 STICs myself. If you were in the NW I would let you test one of my extras before buying.

I’d take you up on testing one of your extras. I’d be willing to pay a rental fee haha you guys ever ride down at Albany Mx?

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5/22/2020 10:57 AM

Swarley814 wrote:

I’d take you up on testing one of your extras. I’d be willing to pay a rental fee haha you guys ever ride down at Albany Mx?

No rental fee needed. We ride Albany occasionally. Used to be my home track for many years now live too far away to be regulars. Would like to get back down there soon though......

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6/1/2020 5:15 PM

CarlinoJoeVideo wrote:

It’s the KTM Factory pipe. I never went back to back with the Fatty. They are shaped a bit different, I think you can split hairs on which one gives your more bottom or mid. I have my bike set up for as much bottom as I can, so it falls off a bit early with my power valve setting.

Sick looking pipe, for some reason not many people know about it.

Is this the pipe?
https://www.ktm-parts.com/50405907000.html

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6/1/2020 9:18 PM

T-Fish wrote:

What exhaust is that? I see the silencer is an Akrapovic, but what’s the expansion chamber? Any difference between that and the full FMF? I may have to spend some money that I don’t need to!

CarlinoJoeVideo wrote:

It’s the KTM Factory pipe. I never went back to back with the Fatty. They are shaped a bit different, I think you can split hairs on which one gives your more bottom or mid. I have my bike set up for as much bottom as I can, so it falls off a bit early with my power valve setting.

Sick looking pipe, for some reason not many people know about it.

It’s this pipe here:
https://www.ktm-parts.com/51605907500.html
Photo
Photo

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6/2/2020 10:56 AM

Is Doma > FMF or PC?

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6/2/2020 11:42 AM

I'm not understanding. You were too lazy to shift the 350 so you got a 450. But you want a 125 off road bike. I'm not busting balls. I just don't understand your reasons

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