KTM TPI Problem? Air Screw and IDLE for KTM Stroke TPI Bikes Explained



Let’s take some time to explain what is going on and how to fix it. Not all of the TPI bikes have a significant issue with this. Some don’t need any work done on them. Each bike is a little different. The issue is that KTM has to lock tight the actual idle adjustment screw to precisely control the amount of oil/fuel/air going into the motor at idle, in order to meet the Euro 4 and Euro 5 emission standards for Europe. Once they surpassed a certain total volume of these production bikes, they became subject to the more stringent emission standards that cars and trucks have to meet in Europe and other places. Given these restrictions, the only way they have given users to adjust the idle speed is by using the “air bypass screw”, commonly referred to as an air screw. All that does is make the mix richer (turning the screw in), or leaner (turning the screw out) with the overall air/fuel mix at idle speeds. While this does have some impact on the idle speed of the motor, it’s causing many of the bikes to be too lean and have a “hanging idle”. That isn’t a good thing. None of my 2019 or 2020 TPI bikes HAD to have this modification in order for me to be satisfied with how they idled, but many others have needed to address this issue. A few of my friends have done this to their bikes with really positive results. After installing the screw that allows you to really adjust the idle by adjusting the butterfly inside the throttle body, you then pretty much close off the air bypass screw most (or all) of the way to enriched the mixture. Some tuning will be required (possible a 1/2 turn one way or another) to get it running optimal when the motor is fully warmed up on your first ride after doing this. I have done this on my 2020 KTM 250 XC in order to show you how to do it and what is going on. The bummer is that most of us will have to use some heat to get the lock tight to loosen up on that set screw that we need to remove. Some of the idle set screw are a T10 Torx, while others are a 2.5mm hex bolt. Mine was the 2.5mm hex. Be careful pulling that out! The only site selling these idle screws that I was easily able to find in the USA was Slavens Racing. He sells them for $30 each. I should be able to get my bike running even better than before on my next ride. Leave a single track everyone!

Here is the video I referred to from Two Stroke Performance. Great vid that I suggest you take a look at –

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