KTM SX250 Sand riders: What MJ at colder temps?

ar15
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ar15
Edited Date/Time 12/11/2020 9:31am
Looking for a baseline to start from. Currently temps are between 3 and 6 °C (37 and 43 °F).
2018 KTM SX250
- HGS Pipe
- Ozzo reed assy
- Only (deep) sand tracks

What MJ do you use under these conditions?
|
AJ565
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AJ565 12/9/2020 12:24pm
12/9/2020 12:24pm Edited Date/Time 12/9/2020 12:25pm
All I've been riding the last for months is sand tracks and GP wide open style sand tracks.
Main jet 500
Pilot jet 32.5
Slide 5.75 (Kawasaki part#16025-0003)
Needle 43-75 (KTM part #55431134400)
Clip position #3 with the colder temps
Needle jet S4 (KTM part #55431021400)
Air screw 1.5-2.0
Fuel 55:1
ar15
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ar15 12/9/2020 1:39pm
12/9/2020 1:39pm
Thank you AJ565. What the local temperature nowadays over there?

Until recently (at 14 deg. C) I used a setup based on your commendations that worked very well:

MJ 490
PJ 35
Slide #5
NDL 43-75
Clip position #3
NJ S4
ASO 1.75
Oil/Fuel 1:32

At 3 deg C. I changed to:
MJ 500
PJ 37.5
NDL 44-75 at clip #3 (1/2 clip richer)
ASO 2.0

Bike still runs great, but when I changed the plug by a new NGK BR8ECM, the plugs' isolator stays quite white, also with a #9 plug. Looks (too?) lean, but maybe I worry for nothing, that's why I'm curious about what MJ others use at low temps.
Cammy41
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Cammy41 12/9/2020 1:44pm
12/9/2020 1:44pm Edited Date/Time 12/9/2020 1:45pm
165mj
38 pilot
NECJ 3rd clip
2019 sx250 with boyesen rad valve
I switched to a keihin from a 2016 sx250 after i had nothing but issues with my mikuni
I ride mostly sand in south west scotland
2
AJ565
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AJ565 12/9/2020 8:16pm
12/9/2020 8:16pm
ar15 wrote:
Thank you AJ565. What the local temperature nowadays over there? Until recently (at 14 deg. C) I used a setup based on your commendations that worked...
Thank you AJ565. What the local temperature nowadays over there?

Until recently (at 14 deg. C) I used a setup based on your commendations that worked very well:

MJ 490
PJ 35
Slide #5
NDL 43-75
Clip position #3
NJ S4
ASO 1.75
Oil/Fuel 1:32

At 3 deg C. I changed to:
MJ 500
PJ 37.5
NDL 44-75 at clip #3 (1/2 clip richer)
ASO 2.0

Bike still runs great, but when I changed the plug by a new NGK BR8ECM, the plugs' isolator stays quite white, also with a #9 plug. Looks (too?) lean, but maybe I worry for nothing, that's why I'm curious about what MJ others use at low temps.
The proper way to read a plug is a throttle chop and then cut the threaded section off and measure the ring at the base of the porcelain. The entire thing can look white (mine was yellow because of the fuel I was running) and as long as you have a 2mm wide ring at the bottom you’re good. Over 2mm it’s rich, less then 2mm is lean.

Leave the jetting you have in it and put a 500 main in it and see how it does. I personally like the bigger mains in these bikes as it picked up some over rev.

Another thing, I run my jetting at 55:1. With you running 32:1 that’s less gas and more oil, which will lean out a bike. Maybe with the 500 main back it down to 40 or 50:1 and see what the plug looks like and how it runs. I’ve done a lot of hours with 55:1 and had excellent wear on the piston so I wouldn’t be concerned with running less oil. Synthetic oils have come a long way.

The Shop

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AJ565
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AJ565 12/9/2020 8:21pm
12/9/2020 8:21pm
This is what I’m talking about with the plug ring.
2
timobijnen84 12/10/2020 12:31am
12/10/2020 12:31am
A friend is picking up a 2019 sx250 up tomorrow. I will jet it this sunday at Eersel. Where will you be riding this weekend? if you are riding this weekend.
ar15
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ar15 12/10/2020 12:56am
12/10/2020 12:56am
Hello AJ565. Thank you. I agree that a throttle chop would be the best thing to do (I've read about it, seen the pictures, watched the YouTube movies). The problem is that there is no way that I can do one where I live, it's a densely populated area and riding a MX bike other than on a MX track is an absolute "no go". The MX racks hardly have a section that's long enough.

I'll stick with the 500 MJ for the time being, maybe richen the needle a bit, and keep a close eye on everything.

About the oil/fuel ratio: We've used 1:32 for all of our bikes, starting with the SX50 15 years ago. I prefer to make a mixture richer/leaner by changing the jetting, not by adding/reducing the amount of oil. The effect of changing from 1:32 to 1:40 is also very small:
1:32=> 97.0% of gasoline per volume of mixed fuel
1:40=> 97.6% of gasoline per volume of mixed fuel
The difference between the two is only 0.6%, or, with 1:40 you will be only 0.6% richer than when using 1:32.
1
timobijnen84 12/10/2020 1:55am
12/10/2020 1:55am
Are you guys adjusting the powervalve at every track or just set it when your changing jetting and do not much more after.
ar15
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ar15 12/10/2020 2:21am
12/10/2020 2:21am
timobijnen84 wrote:
Are you guys adjusting the powervalve at every track or just set it when your changing jetting and do not much more after.
Only changing the spring depending on the trach and/or riding conditions.
ar15
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ar15 12/10/2020 2:22am
12/10/2020 2:22am
timobijnen84 wrote:
A friend is picking up a 2019 sx250 up tomorrow. I will jet it this sunday at Eersel. Where will you be riding this weekend? if...
A friend is picking up a 2019 sx250 up tomorrow. I will jet it this sunday at Eersel. Where will you be riding this weekend? if you are riding this weekend.
Haven't decided yet, but not Eersel.
1
timobijnen84 12/10/2020 2:39am
12/10/2020 2:39am Edited Date/Time 12/10/2020 2:40am
What tracks do you ride at mostly. I am from Boekel so when i dont have to work on saturday and the track is open i am at MC Boekel.
ar15
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ar15 12/10/2020 3:00am
12/10/2020 3:00am Edited Date/Time 12/12/2020 3:03pm
timobijnen84 wrote:
What tracks do you ride at mostly. I am from Boekel so when i dont have to work on saturday and the track is open i...
What tracks do you ride at mostly. I am from Boekel so when i dont have to work on saturday and the track is open i am at MC Boekel.
Most of the time:
- Oirschot
- Budel
- Berghem
- Veldhoven
- Eersel
Less:
- Boekel
- Son
- Stevensbeek
- Reusel
- Lille (Belgium)

timobijnen84 12/10/2020 3:39am
12/10/2020 3:39am
Last year i was almost every weekend at Oirschot but with a little rain it is closed. I dont like Berhem because i have a yz125 and i am not so fast so Berghem is really hard.
jeffoff
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jeffoff 12/10/2020 11:04am
12/10/2020 11:04am
Pull the head and check your piston wash... bottom of your piston crown tells you also part of the story but then cylinder needs to go off as well.

Also, 1/40 with good quality 2 stroke oil is good & safe.
Espescially with the fully synthetic oils we have now...
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Donkey Kong 12/10/2020 2:38pm
12/10/2020 2:38pm
AJ565 wrote:
All I've been riding the last for months is sand tracks and GP wide open style sand tracks. Main jet 500 Pilot jet 32.5 Slide 5.75...
All I've been riding the last for months is sand tracks and GP wide open style sand tracks.
Main jet 500
Pilot jet 32.5
Slide 5.75 (Kawasaki part#16025-0003)
Needle 43-75 (KTM part #55431134400)
Clip position #3 with the colder temps
Needle jet S4 (KTM part #55431021400)
Air screw 1.5-2.0
Fuel 55:1
I'm using your older jetting specs with the YZ needle, is this new setting with the KTM needle worth doing? I was thinking about a lectron? Also how did you come up with these settings cause it's really good! (18' 250sx for reference)
digger
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digger 12/10/2020 5:17pm
12/10/2020 5:17pm
AJ565 wrote:
All I've been riding the last for months is sand tracks and GP wide open style sand tracks. Main jet 500 Pilot jet 32.5 Slide 5.75...
All I've been riding the last for months is sand tracks and GP wide open style sand tracks.
Main jet 500
Pilot jet 32.5
Slide 5.75 (Kawasaki part#16025-0003)
Needle 43-75 (KTM part #55431134400)
Clip position #3 with the colder temps
Needle jet S4 (KTM part #55431021400)
Air screw 1.5-2.0
Fuel 55:1
Donkey Kong wrote:
I'm using your older jetting specs with the YZ needle, is this new setting with the KTM needle worth doing? I was thinking about a lectron...
I'm using your older jetting specs with the YZ needle, is this new setting with the KTM needle worth doing? I was thinking about a lectron? Also how did you come up with these settings cause it's really good! (18' 250sx for reference)
I typically list the Yamaha needles because they are cheaper, usually, they the KTM needles. The needles themselves are the exact same.

The 43-75 needle that AJ uses 1/2 clip position richer than the 42-75 needle. The 42-75 needle in the same clip position as the 43-75,is going to be a little more responsive down low. Is it worth it ? It's up to the individual rider. It's all about having options.

The Lectron carb is not going to have the same hit as the Mikuni, it typically has a smoother type of power delivery. it may be an option for someone who rides at varying altitudes.

Lots of testing. I try to get guys/gals in the ball park jetting wise, but the final setting are up to the riders. I try to provide knowledge as to how to get there.
1
Donkey Kong
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Donkey Kong 12/10/2020 9:10pm
12/10/2020 9:10pm
AJ565 wrote:
All I've been riding the last for months is sand tracks and GP wide open style sand tracks. Main jet 500 Pilot jet 32.5 Slide 5.75...
All I've been riding the last for months is sand tracks and GP wide open style sand tracks.
Main jet 500
Pilot jet 32.5
Slide 5.75 (Kawasaki part#16025-0003)
Needle 43-75 (KTM part #55431134400)
Clip position #3 with the colder temps
Needle jet S4 (KTM part #55431021400)
Air screw 1.5-2.0
Fuel 55:1
Donkey Kong wrote:
I'm using your older jetting specs with the YZ needle, is this new setting with the KTM needle worth doing? I was thinking about a lectron...
I'm using your older jetting specs with the YZ needle, is this new setting with the KTM needle worth doing? I was thinking about a lectron? Also how did you come up with these settings cause it's really good! (18' 250sx for reference)
digger wrote:
I typically list the Yamaha needles because they are cheaper, usually, they the KTM needles. The needles themselves are the exact same. The 43-75 needle that...
I typically list the Yamaha needles because they are cheaper, usually, they the KTM needles. The needles themselves are the exact same.

The 43-75 needle that AJ uses 1/2 clip position richer than the 42-75 needle. The 42-75 needle in the same clip position as the 43-75,is going to be a little more responsive down low. Is it worth it ? It's up to the individual rider. It's all about having options.

The Lectron carb is not going to have the same hit as the Mikuni, it typically has a smoother type of power delivery. it may be an option for someone who rides at varying altitudes.

Lots of testing. I try to get guys/gals in the ball park jetting wise, but the final setting are up to the riders. I try to provide knowledge as to how to get there.
What temperatures for each needle position? I'm going to try out your new jetting.
AJ565
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AJ565 12/11/2020 5:51am
12/11/2020 5:51am
Donkey Kong wrote:
I'm using your older jetting specs with the YZ needle, is this new setting with the KTM needle worth doing? I was thinking about a lectron...
I'm using your older jetting specs with the YZ needle, is this new setting with the KTM needle worth doing? I was thinking about a lectron? Also how did you come up with these settings cause it's really good! (18' 250sx for reference)
digger wrote:
I typically list the Yamaha needles because they are cheaper, usually, they the KTM needles. The needles themselves are the exact same. The 43-75 needle that...
I typically list the Yamaha needles because they are cheaper, usually, they the KTM needles. The needles themselves are the exact same.

The 43-75 needle that AJ uses 1/2 clip position richer than the 42-75 needle. The 42-75 needle in the same clip position as the 43-75,is going to be a little more responsive down low. Is it worth it ? It's up to the individual rider. It's all about having options.

The Lectron carb is not going to have the same hit as the Mikuni, it typically has a smoother type of power delivery. it may be an option for someone who rides at varying altitudes.

Lots of testing. I try to get guys/gals in the ball park jetting wise, but the final setting are up to the riders. I try to provide knowledge as to how to get there.
Donkey Kong wrote:
What temperatures for each needle position? I'm going to try out your new jetting.
Digger is why I have the updated jetting. I had questions I bounced off him and then gave them a try. So far the jetting has been working from 100’s down to the 60’s so far.

I’m am going to point out that the jetting is crisp and the 250 runs like a 250 should. A lot of people find it very violent with the on/off switch type of throttle response. It’s super rideable tho and I love it, power whenever I need it.

Pit Row

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mxstate
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mxstate 12/11/2020 7:03am
12/11/2020 7:03am
I concur...
Got AJ specs on my 19TC250 and snappy (read violent!) is on point.
I am going to richen this setup and play more with the powervalve to tame it a bit.
Nevertheless , the bike runs great, no gargle or hiccup
No longer affected as temp/humidity change
It is running like a 250 should .. and for the fraction of the cost of a Lectron or Keihin (not bashing, I met people who switched and like these carbs)
ar15
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ar15 12/11/2020 8:36am
12/11/2020 8:36am
Coming back to by initial question:

Looking for a baseline to start from. Currently temps are between 3 and 6 °C (37 and 43 °F).
2018 KTM SX250
- HGS Pipe
- Ozzo reed assy
- Only (deep) sand tracks

What MJ do you use in these condition?
Donkey Kong
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Donkey Kong 12/11/2020 9:31am
12/11/2020 9:31am
digger wrote:
I typically list the Yamaha needles because they are cheaper, usually, they the KTM needles. The needles themselves are the exact same. The 43-75 needle that...
I typically list the Yamaha needles because they are cheaper, usually, they the KTM needles. The needles themselves are the exact same.

The 43-75 needle that AJ uses 1/2 clip position richer than the 42-75 needle. The 42-75 needle in the same clip position as the 43-75,is going to be a little more responsive down low. Is it worth it ? It's up to the individual rider. It's all about having options.

The Lectron carb is not going to have the same hit as the Mikuni, it typically has a smoother type of power delivery. it may be an option for someone who rides at varying altitudes.

Lots of testing. I try to get guys/gals in the ball park jetting wise, but the final setting are up to the riders. I try to provide knowledge as to how to get there.
Donkey Kong wrote:
What temperatures for each needle position? I'm going to try out your new jetting.
AJ565 wrote:
Digger is why I have the updated jetting. I had questions I bounced off him and then gave them a try. So far the jetting has...
Digger is why I have the updated jetting. I had questions I bounced off him and then gave them a try. So far the jetting has been working from 100’s down to the 60’s so far.

I’m am going to point out that the jetting is crisp and the 250 runs like a 250 should. A lot of people find it very violent with the on/off switch type of throttle response. It’s super rideable tho and I love it, power whenever I need it.
Sounds like exactly what I want
jeffoff
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jeffoff 12/11/2020 11:16am
12/11/2020 11:16am
ar15 wrote:
Coming back to by initial question: Looking for a baseline to start from. Currently temps are between [b]3 and 6 °C (37 and 43 °F).[/b] 2018...
Coming back to by initial question:

Looking for a baseline to start from. Currently temps are between 3 and 6 °C (37 and 43 °F).
2018 KTM SX250
- HGS Pipe
- Ozzo reed assy
- Only (deep) sand tracks

What MJ do you use in these condition?
2018 TC250
VHM head with higher compression insert (still using 98 fuel)
1.4mm squish
PPS exhaust
Vforce 4
NGK iridium #8 plug
480 main.
Sandtracks

Also rider dependable, fast rider will need richer jetting than slow guy.
So if you have doubts about your jetting check your engine, plug chop, piston wash,...
Or go to reputable shop...
edge60
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edge60 12/13/2020 1:15pm
12/13/2020 1:15pm
I have a 2019 with a vhm 12° piston and head, v force 4 and HGS exhaust and mufler. I ride in Holland mostly on a track part sand, part hard. But sometimes i ride deep sand. I rode the whole summer with mainjet 510 pilot 42.5 and the rich needle that came stock 1 position rich of the middle. I tried with pilot jet 40 and the bike was ripping. But i checked the piston after 3 hours and could see some little marks of detonation. So went back to 42.5 and switched the position of the needle to the middle. Always 1:40 putoline mx9. Piston was clean of carbon after 17 hours. But when the temperature dropped below 20° C i had to go up every time it was 5 to 8° C colder. I could hear it detonate. Last week when it was around 6°C i rode with 550. And it ran wel. My level of riding is quite fast for a vet. When i mounted the VHM kit i had to switch to a richer jetting. So if you ride stock this will probleby rich.

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