Get Your KTM Running Right–From Idle
Story and photos by Jimmy Lewis
With KTM’s new SX-F and XC-F models comes a new Keihin throttle body and it is a little bit different than the norm. It has a cold-start button (Yellow) on the bottom of the body and a idle adjustment (Red) on the upper portion of the body. They are both adjustable but if set improperly (don’t ask how we know, but we learn) they can screw up your bike’s idle, starting and even how it runs.
Here are some quick things you should know:
The Yellow knob on the bottom of the throttle body is the cold-start button. For normal temperatures you should never need it. By pressing it in (upwards toward the body) it clicks in and sets the throttle body’s butterfly valve slightly open to achieve a high idle. When you open and close the throttle sharply, the knob pops back out and releases the butterfly back to normal idle position. The knob is adjustable and is used to set only how high you want the engine to high idle at during cold starting. There are roughly 63 clicks total and the standard adjustment is in the neighborhood of 38 clicks out from fully closed. If you turn the yellow knob in too far, less than 15 clicks out from fully closed, it can start to override the regular idle adjustment and really mess with the way the bike runs. Having it too far out just lessens the speed of the high idle for starting. Adjust this from the non-exhaust side of the motorcycle if the bike is hot to avoid burns.
The Red knob is the idle adjustment. It works by putting pressure on the butterfly valve and determining the stop or closed throttle position. It does not have clicks–just a spring providing tension on the threaded knob adjuster. As long as there is some free play in the throttle cables this adjuster is easy to adjust. Too much tension on the throttle cables can also not allow the butterfly valve to close completely. You can check this by backing the red knob out (unscrewing) so that the bike will not idle. Setting the correct idle speed is bike specific (from 1700-2200 RPM) and there is a recommended RPM quoted in the manual. We have found idle speed is an excellent tuning tool for riders. A higher idle RPM can reduce stalling and the sensation of closed throttle compression braking. A lower idle RPM can give additional compression braking and in some instances the feeling of a more pronounced hit of power. The Red idle adjuster is reached from the pipe side of the bike and is high enough and away from the exhaust so getting burnt isn’t an issue.