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TECHNICAL MOTOBRICK WRENCHING In Remembrance of Inge K. => The Motobrick Workshop => Topic started by: 3dognate on February 20, 2022, 02:02:14 PM

Title: Fuel Pump behavior question
Post by: 3dognate on February 20, 2022, 02:02:14 PM
I didn't have luck finding an answer by searching.

My first K bike ('87 K75C). Was not running when I got it. Just cleaned out the tank and installed a new fuel pump, injectors, lines, and fuel level sending unit. I haven't added fuel yet, but I connected everything up and turned on the power. Now, I'm used it bikes where the fuel pump spins up and the fuel system gets pressurized when the ignition is switched on. It appears that the fuel pump spins when I hit the starter button, but not when I switch on the power. But it's unclear how it's SUPPOSED to behave. Can anyone clue me in here?

Does the fuel pump only run once the bike is spun up and firing?
Title: Re: Fuel Pump behavior question
Post by: Scott_ on February 20, 2022, 03:32:19 PM
For the bike you have, with the Jetronic controller, what you describe is correct.
The pump relay only energizes when the engine is turning(sensed by the hall sensors), or when the starter button is pressed.

The newer bikes, ie the 1100's with the Motronic controller, the fuel pump will prime when the ignition is turned on, then continue to run when the engine is turning.
Title: Re: Fuel Pump behavior question
Post by: rbm on February 20, 2022, 05:25:44 PM
If you are interested in finding out all that happens when you press the start button, read the section entitled "What's happening when you press the starter switch" about halfway down at this URL: https://www.kforum-tech.com/electrical/EFI/bike-wont-start-EN.htm
Title: Re: Fuel Pump behavior question
Post by: 3dognate on February 22, 2022, 02:18:04 PM
thanks