Hello all, 

Firstly I joined this forum not long ago and I appreciate how kind and knowledgeable everyone is. It is nice knowing I am not being laughed at for easy questions on my first K Bike.

Secondly, I have a question here.

I have been rebuilding a 1985 K100. 
When I went to pick the bike up, the bike had great compression trying to start, starter sounded strong, but it was apparent the engine was not getting any fuel. 

To back this claim, I also went and had a listen to the fuel pump and not to my surprise there was no sound. 

I ordered a new fuel pump (before testing… which you will find out why I shouldn’t have later lol)

I wake up this morning and go huh. Let me test my old fuel pump first. I hook it up to the bikes battery with 2 alligator clips and what do you know, the fuel pump works. 

This obviously means that there is an electronic issue with , what I assume, the stem that has the 4 pin plug on the left side of the tank (where all the fuel is delivered) 

Today, I put the tank back on, reconnected the fuel pump properly, and turned the ignition on on the bike. Neutral light went on, but no sound of the fuel pump. 

I’ve heard these 4 pins can be faulty, so what is my solution here 

I need to make note that 

1) the K100 I picked up is pretty much stripped right now of any fairings , seat, etc. it was a cafe conversion that I picked up.

2) this is my first K bike, so I may not be fully up to date on all the terminology yet. 

3) The bikes battery is strong, and when I go to turn the ignition on, the neutral light goes on (good sign) 


Thank you!

Please check this Video I made out  

Are you aware that the pump only runs when the engine is turning or when you press the starter button?

Yes, 

I should have mentioned that. 
I am aware of that, was just trying to give a visual demonstration. 

Thank you.

Tranberg wrote:Are you aware that the pump only runs when the engine is turning or when you press the starter button?

acort wrote:I am aware of that, was just trying to give a visual demonstration.

In the video, you seem to demonstrate that you expect the pump to run when the key is turned to the On position. If you do understand that the pump will only work as intended when the starter is cranking the engine or when the engine is running, and cranking the engine has not resulted in the pump's operation, there several reasons that could be preventing the pump's operation, some of them are:
The four-pin plug connection pins and sockets are too oxidized to transfer current;
The wire connections to the terminals within the plug and sender connections are broken;
The wire connections within the fuel sender to the pump are faulty;
The fuel injection relay connections are oxidized and/or the relay itself is faulty;
The wire connections at the Hall sensor plug are faulty;
The main ground connections at the frame backbone are oxidized;
The plug connections of both the ignition control unit and the fuel injection control unit are oxidized and/ or loose.

Starting at the top of the list, each of these connections should be cleaned, checked for continuity on both sides then followed by cranking the engine to check pump operation. Fully charge the battery before beginning. Allowing it to discharge enough to slow cranking could damage the starter relay.