Posts
7
Joined
6/9/2021
Location
Hudsonville, MI, USA
Edited Date/Time
6/14/2021 11:45am
Hoping to get some advice from some 150sx owners. I just got a hold of a 2022 KTM 150sx and I want to add a few parts to help with performance. I want to see if people have had good experience with some of things I want to do to this bike. If anyone has advice or experience with the following parts it would be greatly appreciated.
I ride mostly MX and plan to do some occasional trail riding.
1. RKtech head with thick head gasket
2. Pro Circuit R 304 Shorty Silencer (With stock expansion chamber)
3. Keihin Airstryker? Is this 100% necessary for the bike to run clean and crisp?
4. VP C12 - Going to run 50/50 with pump gas.
5. 49 or 50 tooth sprocket - Gearing Suggestions?
I ride mostly MX and plan to do some occasional trail riding.
1. RKtech head with thick head gasket
2. Pro Circuit R 304 Shorty Silencer (With stock expansion chamber)
3. Keihin Airstryker? Is this 100% necessary for the bike to run clean and crisp?
4. VP C12 - Going to run 50/50 with pump gas.
5. 49 or 50 tooth sprocket - Gearing Suggestions?
Pretty sure you do not need any power-related mod, the stock power is really good, almost like a 2F with less torque. I also run Pump 91, which might even have a bit more power with race gas.
The only thing I dislike a bit about this bike is the 6-speed transmission. I feel like I am always shifting. Coming from a 2F, two-stroke 6-speed transmission is hard to get it perfect.
Hope this helps, enjoy your bike mate.
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These bikes are so good stock, a lot of aftermarket stuff makes them worse lol.
Rear spring for your weight and maybe your preffered grips. Ktm even offer lower and taller seats that can help dial on the ergos
The FMF Fatty and PC shorty R-304 silencer is the way to go - been dyno tested to be the best combo, although only marginally better than stock.
MXA gearing recommendations (for the 2021 bike, but they're the same):
14/49 for fast/pro
14/50 for tighter tracks/less skilled riders - gets you to 3rd gear faster. I got this setup. will try it this sunday
People absolutely rave about the PWK Airstryker carb - WITH the STIC mod. Sounded too good not to try. I'll try it in a few weeks and see how I like it.
I bought the VHM head w/ interchangeable domes, mostly for better cooling and it looks cool. Seriously considering porting by Lynks Racing - not for more power, but to broaden the powerband so I don't have to shift quite so often. Another member on Vital did this and was very pleased how it really changed the bike. I'm hoping that the porting, coupled with the pWK STIC will produce a powerband a little more like a 250F. We'll see!!!
I'm torn between running straight T2 or maybe just pump gas with 25% C12. I can't get non-ethanol gas here in Commiefornia. The bike ran great with pump gas this past Sunday, so not sure if I really even need any C12 at all.
Now having said all that - you don't need any of that. Like Bruce said, the bike is great stock once you get it running crisp. I just like building cool/trick bikes even if I'm so slow I'll never come close to realizing their full potential. It's a sickness! LOL
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Going to a 14 teeth sprocket gives more top speed and less bottom end. That's why I kept the 13 teeth stock sprocket and went for a 50 teeth rear, to get more bottom.
What they left out is going to a 14t front sprocket also changes the chain angle and let’s the rear suspension work better because it’s on less of a bind.
Personally if it was my bike and I needed more bottom end I’d be running a 14/52, but I’d be giving up top end or adding in another shift because the engine maxed out before the section did. Having ridden the 150’s tho I feel I’d be happier based on my skill set at a 14/50 on a wide open track and a 14/51 on a tighter track.
Gear ratios are pretty cool to test with. On my 250 stock is 13/50 (3.846) and the popular thing to do is run a 13/49 (3.769) which helps a lot. I learned about the chain angle thing so bought cheap sprockets (in case I didn’t like it I wasn’t out much money) to test with and went to a 14/52 (3.714) and while not as much of a change as going from a 50 to a 49, what was more noticeable was how the rear suspension worked and felt much more free.
Gear chart for reference
More top speed/less bottom
14/48 3.428
14/49 3.5
14/50 3.571
14/51 3.642
13/48 3.692 (stock)
14/52 3.714
13/49 3.769
13/50 3.846
More bottom/less top speed
On topic, follow the jetting thread fully, don’t just get part of the parts list and be disappointed in reading how it changes the bike and then it’s not much different. Adjusting the power valve is also a big tuning tool. I like to start at 1 3/4 turns in from all the way out. Need a little more hit at low end? Back it out. Need a little more mellow hit? Turn it in. 1/4 turn makes a big difference so start with those adjustments. Don’t be afraid of trying different settings either, you may like it more then you thought with the power band in a different range.
Link
I went to a 50T rear because the bike was bugging real bad on stock jetting for me and I also had an issue with burning transmission oil on the bike brand news which clearly did not help the jetting.
Going to a lower number, such as from 3.692 to 3.500, will have the exact opposite effect of what they are saying. It's a taller gear which will be harder for the small engine to pull, cause more bogging, and be harder for a novice to keep on the pipe. Tight corners will require 1st gear instead of 2nd. See AJ's chart above for the right info.
As for the Power valve adjustment, my experience with my 125 is opposite of what AJ is saying. If I turn the adjuster out (less preload) it softens the hit and the bike doesn't get on the power as easily. Basically the PV is opening too soon. If I turn it in and retard the PV opening, it pulls really hard initially, like too snappy, but then falls on it's face as it's waiting for the PV opening to catch up. The trick is to find the sweet spot in between there. A 250 might be different than a 125 since the engine has more power and might actually respond harder to the PV opening sooner.
Milled down the head and cleaned up the ports, thicker base gasket to get the squish right
modded the carb (pretty good write up on thumper talk)
FMF Fatty/Shorty combo
Vforce4 reeds
50t
As stated above, you can get these stock carbs to work really well. I thought about a Lectron before I started hacking on mine, but was pretty pleased with the results.
https://www.vitalmx.com/forums/For-Sale-Bazaar,26/KTM-NEW-PARTS-Upgrade…
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