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Last active Mar 25, 2021
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2018 Kawasaki KLX250 EFI Throttle Body

Blog 2021/3/2

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2018 Kawasaki KLX250 EFI Throttle Body

I'm planning on designing a DIY EFI controller for my 2009 KLX250SF, and part of that is retrofitting a suitable throttle body onto the bike. I purchased a used throttle body from the 2018 version of my bike for this purpose.

Here are some notes on it.

Interface to air filter

The main spigot which connects to the air filter box is 55mm in diameter, with a small lip of 56mm.

The 55mm portion is about 11mm in length, with the lip positioned about 4mm in from the (air filter) end.

Interface to engine

The spigot which connects to the engine intake is 50mm in diameter, with an indentation which is a little less than 1mm deep, positioned about 4mm in from the end.

Main butterfly valve

The main butterfly valve is 34mm in diameter.

Stepper-controlled butterfly valve

The stepper-controlled butterfly valve is slightl ovoid, ranging from about 38.1mm (vertical) to about 36.8mm (horizontal).

Stepper motor

The stepper motor has a four-pin connector.

Wire colors (looking into the connector, tab on top, starting upper right and moving clockwise):

  • Green
  • White/Green
  • White
  • Black

I measure about 6.4 Ohms between Green and White/Green, and between White and Black.

Throttle position sensor (main)

The main throttle position sensor is... a bit strange? The resistance which doesn't change is 4.83k, yet two of the pins which vary in resistance measure 4.99k at closed throttle. Weird.

It pin 1 is closest to the engine, I measure 4.99k from pin 1 to pin 2 at closed throttle, and 1.95k at wide-open throttle.

Throttle position sensor (stepper-controlled butterfly valve)

The throttle position sensor attached to the stepper-controller butterfly valve is a 4.7k potentiometer.

If pin 1 is closest to the bottom of the throttle body (furthest away from the fuel injector), I measure about 4.36k at closed throttle and about 1.11k at wide-open throttle.

Fuel injector

I measure about 10.3 Ohms DC resistance.

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