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Carb/jetting help?
- Thread starter ajaxguy
- Start date
Someone with more experience, please correct any of this if I'm wrong.
From what little I understand of it, it's complicated, time consuming, and involves a lot of black magic. Is there something specific you want to know?
It involves replacing the jets and/or needles with different sizes and/or shapes to get the desired affect. Each carb is different but it's safe to assume yours has at the very least a main jet and a needle. The jet can change size, the needle can change size and/or shape, and can be raised or lowered with a clip.
Generally you try and understand how your engine is running. That involves feeling how it pulls, whether it backfires, runs hot, or smells like gas, and what the spark plugs look like after running for a bit at a given throttle setting.
Once you think you know what the problem is, you rip everything apart, buy and replace some needles and jets, and put it back together. Hopefully it runs better, not worse. Rinse and repeat until you reach perfection, or more likely don't care anymore.
I changes the jets on my GS500, but it was a very easy process. That bike has been around for about 30 years and there is a huge amount of knowledge around how it runs and what jets are best for any given setup. I knew exactly what it needed and just had to put them in. With something newer and less popular, you are likely on your own.
You also might be able to get a dynojet kit if they make one for your bike. Then you'd have some guidance and maybe some over-the-phone support, but opinions on those kits vary wildly.
From what little I understand of it, it's complicated, time consuming, and involves a lot of black magic. Is there something specific you want to know?
It involves replacing the jets and/or needles with different sizes and/or shapes to get the desired affect. Each carb is different but it's safe to assume yours has at the very least a main jet and a needle. The jet can change size, the needle can change size and/or shape, and can be raised or lowered with a clip.
Generally you try and understand how your engine is running. That involves feeling how it pulls, whether it backfires, runs hot, or smells like gas, and what the spark plugs look like after running for a bit at a given throttle setting.
Once you think you know what the problem is, you rip everything apart, buy and replace some needles and jets, and put it back together. Hopefully it runs better, not worse. Rinse and repeat until you reach perfection, or more likely don't care anymore.
I changes the jets on my GS500, but it was a very easy process. That bike has been around for about 30 years and there is a huge amount of knowledge around how it runs and what jets are best for any given setup. I knew exactly what it needed and just had to put them in. With something newer and less popular, you are likely on your own.
You also might be able to get a dynojet kit if they make one for your bike. Then you'd have some guidance and maybe some over-the-phone support, but opinions on those kits vary wildly.
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ajaxguy
Well-known member
ya I dont even know if I need to get into that much, just based on the idle screw and the carb screw on the side that i can see... Like i read stuff about x amount turns out on the carb screw and then match that up with the idle..just no sure how many turns out even the damn carb screw has to be out?
Oh yeah, you can start with the idle adjustment and the idle mixture screw.
Try this: https://www.youtube.com/watch?v=YxpQjDQzX7g
Try this: https://www.youtube.com/watch?v=YxpQjDQzX7g
Jimsun
Well-known member
Whats the bike? If its idling too high and no idling screw, you can adjust the idle via carb synching. You have to, i believe, lower the pressure (this is how my bike works with my carb synch). If you dont have a carb synch tool, you can bench synch it if your carb 2(for hondas) is preset.
Last edited:
cbcanada
Banned
Assuming you went up one size in jets and assuming since you bike is a 50 it only has two jets
Did you change both the idle and main jet?
If you went one size higher on the idle then you are probably running rich
To confirm take out your spark
Plug and clean it. Them put it back
then turn bike ok and let idle for 5 min.. Do not roll throttle at all. Then turn off bike and take out the spark plug if its grey and dry its lean.. But i bet it will not be and it will smell
If gas even cause your bike is running rich.. So you need to roll back the air mixture screw to let more air in. Its very sensitive to find the right mixture...
Anyways if you want dm me and i give you my number.. Too much to write
Did you change both the idle and main jet?
If you went one size higher on the idle then you are probably running rich
To confirm take out your spark
Plug and clean it. Them put it back
then turn bike ok and let idle for 5 min.. Do not roll throttle at all. Then turn off bike and take out the spark plug if its grey and dry its lean.. But i bet it will not be and it will smellIf gas even cause your bike is running rich.. So you need to roll back the air mixture screw to let more air in. Its very sensitive to find the right mixture...
Anyways if you want dm me and i give you my number.. Too much to write
ajaxguy
Well-known member
Assuming you went up one size in jets and assuming since you bike is a 50 it only has two jets
Did you change both the idle and main jet?
If you went one size higher on the idle then you are probably running rich
To confirm take out your spark
Plug and clean it. Them put it back
If gas even cause your bike is running rich.. So you need to roll back the air mixture screw to let more air in. Its very sensitive to find the right mixture...
Anyways if you want dm me and i give you my number.. Too much to write
I didnt change anything....I just messed with the idle screw and adjustment screw. As many bikes as I have had, I have never messed with the carbs and jetting so Im new with this. Seems to be running fine, but he is going to be racing this thing so just wanna know how to have it running at peak performance.
Ya I read about that but I guess im an idiot, cuz I do not understand what they mean by this
ajaxguy
Well-known member
considering that....cant be more then an hours work im assuming
Jimsun
Well-known member
prob take less than 30 minutes if the pro knows his stuff and your bike.
Iceman
Well-known member
^this. I have owned numerous two strokes over the years, bit finicky getting the jetting right, but when you do = heaven. There is an excellent post on jetting on the ODSC website, helped me immensely. I can also guarantee that the guys at OCMC will gladly give advice/help, mini-moto dad's stick together! Great attitude, never be shy about asking for help, those guys at the track will respect you more for it. Try to get to the track/club on a non race day, the guys will have more time to help explain it to you. While you're at it, find out what you can about the clutches in that 50, they are adjustable and make a big difference in how aggressive the bike rides.
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It just means record where the screws are before you touched them. Your first adjustment should be slowly turning them all the way in and counting the rotations. That way if things go horribly wrong, you can at least put everything back the way it was.
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ajaxguy
Well-known member
Ya I have only been to one meeting, so do not know anyone yet to ask for help, I have no shame is asking, just dont know anyone and i want them setup before race day.
I have two now.. 2003 KTM 50 mini adventure and a 2008 KTM junior Sx 50.
I have touched it so many times though! lol
Iceman
Well-known member
Ok for the 08 50jr sx, lightly turn the air mixture screw ( small flathead closest to the airbox) all the way in ( lightly seated, don't tighten it down, it'll damage the needle) then back it out 3.5 full turns. This is factory setting. Fire it up, adjust the idle speed via the idle speed screw ( larger thumbscrew in the centre of the carb body) just adjust to a good idle speed, no specific setting. Take it for a rip, check plug colour, you can adjust for a rich/lean condition with the smaller air mixture screw tha you earlier set to. 3.5 out. Then readjust the idle speed as needed. Small 1/4 turns only with the air mixture screw, then try it. A little spooge (oil residue) from the exhaust is ok. You want a clean, snappy throttle.
The 50 mini is the same process except that as far as I can tell , there is no air mixture screw. Simply adjust idle speed via the throttle stop screw ( again, the large thumbscrew in the center or the carb body.
Ktmdirtquestions.com. Great site, online manuals etc. thumpertalk.com an off-roaders best friend
Hope it helps. Good luck to the little guys, hope they have a lot of fun this season.
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The 50 mini is the same process except that as far as I can tell , there is no air mixture screw. Simply adjust idle speed via the throttle stop screw ( again, the large thumbscrew in the center or the carb body.
Ktmdirtquestions.com. Great site, online manuals etc. thumpertalk.com an off-roaders best friend
Hope it helps. Good luck to the little guys, hope they have a lot of fun this season.
Sent from my iPhone using Tapatalk
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