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You should really adjust the power valve before you make any more changes as it will affect the jetting. I just use a flat blade screwdriver to adjust them. After getting that set if you still have a bog swap out the jetting. FGR's small bore specs. are pretty spot on.
Just to add to this- if you want an easier way to play with your power valve setting prior to fine tuning the jetting based on the “hit”- check out Kreft Powerdial 3.0 it makes this adjustment doable by hand. I use it on all my bikes. Great if you bounce between track and trail
This is more of a curiosity post: I have ran AJ’s spec on 2018 KTM 250sx and a 2019 KTM 125sx with great results using Amsoil Dominator 50:1 (per oil manufacturer spec)with 93 ethanol free pump gas due to the low flashpoint and clean burn.
Question is what’s everyone else running for fuel combo? I ride with my son a lot who is intermediate so a lot of on/off throttle and pilot to needle jet zone….not really much main jet riding haha. As he progresses and when I’m riding harder should I look for a 40:1 mix to get more life out of my top ends? Curious on logic from others.
The 125 you should run 40:1. In my 250 I run 60:1 and it’s wide open a lot. I have 175 hours on the bike and have done 1 bottom end and 2 top ends in that time. Actually the only reason I did a bottom end is because I got ahold of that bad batch of T4 and the fuel gelled and trashed the crank thrust washers.
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In my 125 and 250, which are now 150/300, I run 38:1. Partly just for the simplicity of 1 gas jug. But also I just don’t really trust the higher ratios, especially in a 125. We’ve all seen the pics of the 250/300 scattered engines when they stick a piston and yank the wrist pin out. I’m have a theory that the 250/300 has that huge oiling slot in the rod because of the 60:1 ratio. Keep in mind the 125 does not have that big slot and is somewhat prone to the wrist pin getting hot.
I finally Buy a clean 2020 150 sx with 45hs . I will order 5# slide , 500,520,540,560 mains and 32.5,35,37.5 pilots . Sea level , 40:1 Motul 800 /710 . Fuel pump 93. And Jet block gasket and float needle oring.
I'm a little confuse on the needle , 42-74 already on the list but i would like to order the next richer needle for low temp and Sandy situation . 43-74 or 42-73 ??.
Get the 43-74 as an optional richer needle. The clip grooves are 1/2 a clip richer than 42-74 so you can make small adjustments going between the 2 needles.
Thanks and the float height 8-8.7mm should be set with the carb at 45° or the upside down method ?
About 45 degree. Basically you need the tab touching the plunger on the needle, but not depressing the plunger in.
#5 slide
S4 needle jet
42-74 second clip
35 pilot
520 main
Air screw 1.5
I use 90 ethanol free pump gas mixed 40:1 with castor 927. I adjusted the power valve to 2.25 turns in from fully out. The jetting change from above helped a lot but I am still having a slight bog when rolling on the throttle. I also have a question about what spark plug you guys are running. When I bought my bike it had a br9ecm in and I have not changed it. I appreciate the help I am new to tuning carburetors.
What are current temps and elevation?
Have you verified the float height at 8-9mm? Many seem to come around 11mm which is a little too lean.
Before you do anything else, try adjusting the air screw to maybe get an idea of which direction to go on the pilot. Go in to 1.25 turns from closed. Try that. Then go to 1.75 turns and try that. If 1.25 is better, you need a 37.5 pilot.
The BR9ECM should be fine, but I run the BR9ECMIX. You can throw a fresh plug in just to rule that out.
Currently 70-80f at around 500f of elevation. I tried to measure the float height with a digital caliper but I couldn’t get a super accurate measurement. I measured it at around 7-8mm. I’m honestly not for sure where to take the measurement. I have seen a video of someone doing it by blowing into the fuel inlet and my understanding is when you are not able to blow more air in then that’s when you want to take the measurement?
In this video, it's a different model of carb, but he explains the process pretty well. https://youtu.be/Qk5_wTJbTHQ
So, to make the #4 slide into to#5 slide, i have to cut 1mm in the red mark with a round file ( by hand or use a demel) ? . Also i need to take some on the green mark ? .
This is my first time doing it. Any tips where to start ? . make a 0.5/1mm mark with a caliper , start cuting in the middle of the arch and then file to the sides maybe ? .
I apreciate Your help .
@AJ
I've got a 22 150sx, followed fgr's suggestion of the 42-75 needle and went for a leaner main and pilot as was recommended for pump fuel, current specs are:
520 Main
35 Pilot
42-75 needle, 3rd clip
s4 needle
#5 slide
AS 1.75
Running 40:1 on 91 pump fuel
Bike felt pretty good when riding Tuesday, I would say the bottom end felt noticeably better then before, but when opening up the bike out of a corner and getting into the midrange the bike would stutter a bit. Not sure exactly how to describe it as it wasn't a bog, but a bit of a pause before clearing up and running fine on the top end, temp was around 80 deg F. Any suggestions on how to clear out that stutter would be great, thanks to everyone for all the great information here.
Go leaner on the needle clip. Try 43-75 on clip 2. If you don't have the 43 needle handy, try 42-75 on clip 2 just to tell if leaner is better, but you don't want to go too lean. 43-75 is a 1/2 clip richer needle, so you can split the difference with it and not do one whole clip jump. You may also be better off with a 32.5 pilot, especially if it is muggy with the heat.
Pit Row
@digger @AJ565 @FGR01
Dear all,
I have the following setup as you mentioned, but I'm experiencing the same issue, although it's not as noticeable. At low throttle (barely pulling it), as soon as the slide moves, the bike leans out. In neutral, the rpms slowly increase to the moon :D. When driving it cold, it bogs with the same barely pulled throttle. It's under 1/8 throttle. The bike runs well on idle and at higher throttle positions. What solution do you recommend?
/100 m elevation, now at 30 °C (86 °F), but it's the same in cold 5 °C weather. Fuel is like the 93 premium in USA with 1:40 Motul 800/
Pilot--35
Needle--42-75 in #3 clip position
Main--500
Needle Jet--S-4
Slide---5.5,
air Screw---between 1 and 1.5
Thank you for your answer in advance!
This is a recent change? It was running good on these settings before?
I would think jet block gasket, or air leak. Possibly the seal on the carb cap sucking air? Might be a small circuit in the jet block clogged with dirt. Have you verified the float height? May be set too lean.
1. I bought the bike last year with OEM carb internals.
2. It fouls the plug, so I changed the block gasket in the carb to the JD type.
3. I bought the carb internals as you and digger mentioned, but it was really lean in low throttle, needed to close the AS.
Pilot--32.5
Needle--42-75 in #2 clip position
Main--500
Needle Jet--S-4
Slide---5.5,
air Screw---1.5
4. Updated the carb internals as digger update (actual setup), and it's way better, but still bogs when cold and feels lean when hot under really low throttle above idle throttle position. Just turn the throttle like 1 or 2mm, the slide moves a bit, and it leans out. Idle is spot on, higher throttle is good:
Pilot--35
Needle--42-75 in #3 clip position
Main--500
Needle Jet--S-4
Slide---5.5,
air Screw---between 1 and 1.5
It's a recent change to the bike; the issue is constant after the new jets, not changing.
First thing I would do is verify the float height.
The float height was 6.5mm when it fouls the plug originally but I increased it to 8mm.
OK, 8mm should be about perfect. Maybe double check it to be sure.
I will check it, any further tips? Is it possible that I need a bigger pilot jet? Or a sharper jet needle?
I did use 37.5 pilot sometimes when my bike was a 250. Easy to try.
Hello brother
Ive been using the jetting setup for the 150sx succesfully. 53°F sea level
5 slide, 37.5 PJ, 500 main , 42-74 3 clip , 40:1 motul 800, 93 oct pump gas . The problem is im a beginner and im not riding WOT, only in the straight part of the track .
i go down to 35 PJ and 2 clip and the bike runs clean and beautiful . The problem is after 4 hours of riding when i turn it off, then i couldnt start up again . I change the spark plug and starts in the first kick and keep running excellent. I think the problem is my riding and not the jetting , im lugging in 3rd sometimes . Im thinking of changing the premix oil to the Motul 710 that has a lower flash point than the motul 800 .Do you think is a good choice or i should try to run a little more on the pipe . Bike runs beautiful, it doesnt sputter or hesitate , just after a few hours, the spark plug is fouled a bit.
Another solution i was thinking is before turn it off , i do in a straight line a few WOT passes to burn the oil .
Yes, all good thoughts. I've always found Motul 800 to be very clean burning despite the very high flash point. But, yes, give 710 a try. Also, giving it a good blowout before shutting it off is a good idea too. What plug are you running? I run the BR9ECMIX. I think the skinny Iridium tip is supposed to be more foul resistant.
BR9EIX and the last one that fouled is BR8EIX and is new . Thought the hotter plug maybe will help . I think i will try the 710 oil because i like how the bike is running , dont think is the jetting
2022 KTM 250sx with the first setting mentioned.
Is the air screw 1.5-2.0 out from all the way in? And why would fuel leak from the vent hose on the bottom of the bowl?
Also, I have the 32.5 pilot in and did some trail riding this weekend. Maybe sounded a touch lean on the bottom it would ping up a bit, would going to a 35 pilot be a great starting point to adjust?
Thanks!
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