On the left side of the carb you will see a screw with a spring on it, turn this clockwise to lower tickover and anti clockwise to raise tickover.
If your on the right side of the bike the carburetor is to the top left of the cylinder, there is a screw with a spring on it, tighten the screw to bring the idle up, loosen it to lower the idle
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Carb. idle screws are set so thew vehicle idles they are not set at a specific number of turns. With the screw turned out but still in the carb start the vehicle. Let it warm up then turn the screw in until the engine will just idle. There are other adjustments that may assist are to the pilot fuel/air screw. This should be screwed all the way in until it lightly bottoms then turned out 2 turns to start. Once the bike is idling per above turning this screw until it idles at the highest point. This should be between 2 and 3 turns out. Readjust the idle screw to the lower idle if needed and you will be ready to go.
It doesn't idle well because it isn't meant to idle, it's a race-ready bike. The KTM 125 SX is made with many aftermarket parts and they are very high quality machines. The mechanic at the dealership was just telling me today (just picked up my own 125 SX yesterday!) that it's something to do with the air/fuel ratio, and he told me that they could adjust it for me to idle, but the bike is not meant to idle and doing so could result in long-term damage over time. But if you're ok with that, then just go ahead & adjust the carburetor, it's simple. Locate the carburetor screw (check online or in your owners' manual for it's location), and while the bike is running, adjust it about 1/4 turn in the direction that would increase the flow of fuel through the carburetor (again don't ask me, it's either clockwise or counter-clockwise) and continue to let it run. Give it some gas, let it come down, you should be able to tell if it's going to stall, in which case you give it some more gas, keep it running and make adjustments accordingly to find the idle level. Enjoy!
The type of carburetor on the 1999 Yamaha YZ 125 is Mikuni how ever the sub model is either VM TM or TMX
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what is the needle valve adjustment on a 125 DR
36mm Keihin PWK
90% of the time, you can get by with just pulling the main and idle jets out, cleaning and blowing through them to make sure they are not clogged. If that doesn't do it, click the link below and it will walk you through a complete carb rebuild.
is 80 to 125 high
1500 :)