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Who has a old K75 / K100. Finally here's some real technical information about your bike that you can use and understand your vintage motorcycle a little bit more. Strange to think the last built of this series was 20 years ago.

As always with Bayerisch Motoren Werke this motorcycle was built there way or no way. L.E. Jetronic, L.E. is not french but does mean Luft European Jetronic is the name give by Bosch. L.E. Jetronic was engineered for the American market, to meet with at the time meet with new emissions standards in the us.

As you have probably already have noticed your K series has 2 if its a ABS model 3 modules, Rather difficult to troubleshoot compared to the old Airhead bikes. The first one is under the fuel tank is the Ignition control unit (ICU), Under the seat is is the Fuel Injection Control Unit (L.E. Jetronic). If your bike is a ABS model in the tail section is the ABS Control Unit. Above all popular belief it takes these modules quite a bit to go bad.

L.E. Jetronic works with 4 electrical components fuel related, Fuel Pump, Fuel Injectors, Coolant Temperature Sensor, Temperature Switching Unit. and 4 vacuum components / fuel delivery components, Fuel Pressure Regulator, Pressure relief valve, Fuel Rail, Fuel Door (Has a Rubber flapvalve). 4 electrical components air related, Airflow Meter, (same as Mass Air Flow Sensor) Airflow sensing flap, Intake Air Temperature Sensor, Throttle Position Sensor. 4 nonelectrical components, Air Filter Housing, Air Intake Collector, Throttle body(s), Crank Case Vent (no PCV valve). After all this there's good news, News no EVAP valve AND no Vapor Canister.

The I.C.U. is in control of the L.E Jetronic. the fuel injectors are triggered by the Halleffect sensor(s) (Camshaft Position Sensors or Hallsensors) same as the ignition coils. The Fuel Injectors activate after the Hallsensors give there signal to the I.C.U. then to the L.E. Jetronic giving signal to ground the circuit for the Fuel Injectors.

Why is the Coolant Temperature Sensor and the Temperature Switching unit apart of the L.E. Jetronic? the two work together to protect the engine from overheating. I.E the cylinders swelling and the pistons seizing. The Coolant Temperature Sensor is not a switch, Its a Varistor. The hotter it gets the more resistance it offers eventually opening the circuit for the Fuel Injection and Ignition Coils.

Up til now I've mainly talked about the electronic portion of L.E. Jetronic, all the vacuum lines mention above and the Crankcase Ventilation are really only controlled vacuum leaks. the Crankcase Vent has no valve in it what so ever but does provide a passage to the air in take to stabilize internal engine pressure. the Pressure Relief Valve zeros any pressure in Fuel Tank to match pressure on the outside of tank to allow fuel flow with ease.

The Fuel Pressure Regulator is after the Fuel Rail. The Fuel Pump must build enough pressure for the Fuel Injectors then the Pressure Regulator returns the excess fuel to the Fuel Tank.

I didn't intend to have any trouble shooting information in this post but to offer information for anyone to gain a better understanding of there bike.
As far as the L.E. Jetronic charging system that will be in a whole different post.
 
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