1986 k100 fuel pump issue

[EastCoastK100]

   Hey all, I'm new to motobrick. After seeing all the wonderful kbike builds I decided to get one for myself. I picked up a 1986 k100 without fairings. For the most part it is mechanically sound. Besides a leaky fork seal it ran strong.

  Here is the issue I am having and after running many searches I haven't found anything pertaining to my particular issue. Some times after starting the motor I would hear the fuel pump shut off and the bike would stall. So when I would restart the bike the pump would come on and after turning the motor over I would hear it stop. I found that after starting the motor I could bang on the gas tank near the location of the fuel pump and It would start back up again before the motor stalled.

   I assumed the pump was starting to go out so I ordered a new one and installed it. The bike seemed to be running great for a while but when I was on the highway I could feel the pump shutting off and on till it stopped me completely. I pulled over and it was the same deal. After turning the key switch on I could hear the pump and it would shut off after starting. A quick rap on the tank and I was back up. I'm starting to think the fuel pump may not have been the issue. Has anyone encountered this problem before? Is the pump controlled by the Ecu? Any help would be greatly appreciated.

[Martin]

Welcome to the asylum from the land of OZ. The four pin connector under the RH side of the tank that supplies power to the fuel pump is a known source of problems. Some inmates replace them with waterproof four pin connectors to eliminate the chance of problems. However the connector can often benefit from the application of Deoxit and Dielectric grease.
Regards Martin.

[Laitch]

Do as Martin recommends and report back with the result. You are on your way to cleaning all electrical connectors on the bike. While you're at it, be sure the main control plug under the seat is firmly connected.

[EastCoastK100]

As soon as I get home I will check the connections and let you all know. Thank you.

[Brad-Man]

This may be dumb but you didn't state that you cleaned out your tank and replaced the fuel filter on the pump inlet...

If not the filter could be loading up and unloading under the circumstances you have described...

[Laitch]

Here is the issue I am having and after running many searches I haven't found anything pertaining to my particular issue.

:giggles You must have been trying to find one with your name mentioned in it because this is one of the most common problems with these old bikes on the verge of salvation.

Read this entire link—not just the troubleshooting section—to understand how your bike works, when it works. Visit the Technical Library here. Approach the problem step-by-step. Avoid theorizing. Fuel flow could be part of this, as Brad Man has indicated. First check the main plug. You shouldn't be able to unplug it without prying the latch. Then clean the connectors. If that doesn't help, let us know what the inside of the tank looks like.

Post a photo of the bike.