Hey guys, 

Sorry if this is the wrong sub form for this. I am new here. 

I just picked up a 85 K100
I’m planning on building it up. 
The owner showed me a video with a time stamp of it running around 3 weeks ago. 

When I arrived to look at it, the bike wouldn’t start. Strong compression, and the starters sounded like it wanted to start bad but it wouldn’t. 

I build cars, so I know what to look for. 0 sound of the fuel pump turning over. 
I bought the bike, brought it home, and then tested the fuel pump. Nada. 

So I ordered a new fuel pump and filter 

I drained all the old crappy gas and cleaned the lines.
Am now cleaning the inside of the tank. 

My question is, before I install the fuel tank again and the new pump and filter, should I do anything else fuel / engine related before trying to start it up? 

Just did a coolant flush
Going to do an oil change
Spark plugs all look healthy

Let me know what else I should do? 
Or anything else I should look for before proceeding with anything else. 

Thanks guys.

Change all the fuel lines. These inside the tank need to be ethanol resistant and fuel proof both outside and inside, with 2 layers : common fuel lines won't last long as they have only one layer inside.

jbt wrote:Change all the fuel lines. These inside the tank need to be ethanol resistant and fuel proof both outside and inside, with 2 layers : common fuel lines won't last long as they have only one layer inside.

Thank you. 

Do any local stores have a special type?

Or where should I order online.

Fuel pump not runnng may be due to a bad connection in the connector for the fuel tank.  Clean it with Deoxit and make sure the pins can make good contact.

Also, the fuel pump only runs when the starter is pressed and then for a second or two when it is released if the engine isn't turning more than 700 rpm.

Fuel line for use in the tank is grade SAE J30 R10.

Point-Seven-five wrote:Fuel pump not runnng may be due to a bad connection in the connector for the fuel tank.  Clean it with Deoxit and make sure the pins can make good contact.

Also, the fuel pump only runs when the starter is pressed and then for a second or two when it is released if the engine isn't turning more than 700 rpm.

Fuel line for use in the tank is grade SAE J30 R10.

Thank you for this info and your insight. 

In the event that I have a bad connection and and cleaning it / good contact don’t work… how would I proceed? Would I purchase a new “in take electronic unit”

I’m not sure what the name is for it. The black stem inside the tank that has the two wires is what I’m referring to.

Point-Seven-five wrote:Fuel pump not runnng may be due to a bad connection in the connector for the fuel tank.  Clean it with Deoxit and make sure the pins can make good contact.

Also, the fuel pump only runs when the starter is pressed and then for a second or two when it is released if the engine isn't turning more than 700 rpm.

Fuel line for use in the tank is grade SAE J30 R10.

Also, just grabbed some J30 R10 for inside the tank. 

I assume J30 R9 will work for the exterior parts?

The 'black stem' is the fuel level sender and accounts for two of the wires on the 4 pin plug under the LH side of the tank. The other two are for the pump. 
In cases where the fuel pump isn't running, on an early bike like yours, the 4 pin plug is very often the culprit. 

If the plug turns out to be the cause, then BMW very thoughtfully supplied a spare which you can find in the electrical relay box under the seat (only kidding, the 'spare' plug is for an optional extra - just cut it off and graft it onto the wires to the tank)

Before you get that drastic! try closing up the female terminals in the plug by using a (very) small screwdriver. If that is the problem, this very often fixes it.

Be aware there is a need for having the neutral light on, or the clutch pulled in as there is a clutch switch. Replacement switch is cheap if needed.

As said, replace everything in the tank, but that plug on the tank, do as Dai says, been there too. I would also replace the outside tank hoses and Honda ones fit.

Small cost, replace the vacuum caps, vacuum lines and Z crank case vent. Early 85 with bolted down gas tank have a vacuum line at no 1 cylinder, replace it with a vacuum cap.

I got tired of fooling around with this inferior plug BMW used for such an important connection so I replaced it with a waterproof marine 4 pin connection. It was cheap and an easy fix . Mine was always causing me problems like no starts and cutting out now and then while riding.Since I put this in 2 years ago the bike has run flawlessly and I now have total confidence  in it .This is what I used 
4 pin connect link

acort wrote:In the event that I have a bad connection and and cleaning it / good contact don’t work… how would I proceed? Would I purchase a new “in take electronic unit”
I’m not sure what the name is for it. The black stem inside the tank that has the two wires is what I’m referring to.

That model of fuel level sender has been obsolete for around 35 years and new replacements haven't been made for many years. Later senders are used on tanks that have receiving openings on the right-hand underside. Those senders are also out of production right now and difficult to find in good condition.

The upstream side of that four-pin connection gets its current from the fuel injection relay when the starter is cranked or the engine is running. You need to rule out a faulty fuel injection relay if cleaning and adjusting the connection pins doesn't doesn't help despite the wire connections within the plugs being okay. 

The fuel pump doesn't start until the engine is cranked but it can be heard whining for a couple of seconds after cranking stops.

Laitch wrote:

acort wrote:In the event that I have a bad connection and and cleaning it / good contact don’t work… how would I proceed? Would I purchase a new “in take electronic unit”
I’m not sure what the name is for it. The black stem inside the tank that has the two wires is what I’m referring to.

That model of fuel level sender has been obsolete for around 35 years and new replacements haven't been made for many years. Later senders are used on tanks that have receiving openings on the right-hand underside. Those senders are also out of production right now and difficult to find in good condition.

The upstream side of that four-pin connection gets its current from the fuel injection relay when the starter is cranked or the engine is running. You need to rule out a faulty fuel injection relay if cleaning and adjusting the connection pins doesn't doesn't help despite the wire connections within the plugs being okay. 

The fuel pump doesn't start until the engine is cranked but it can be heard whining for a couple of seconds after cranking stops.

Thank you. Where might I find info on / locate the fuel injection relay?

acort wrote:Where might I find info on / locate the fuel injection relay?

Go to this webpage and scroll down to the LE Jetronic Training Manual. It will explain your Brick's operating system, including the fuel injection relay.

Go to the Tech Page in the Portal here at the K100-forum and download the Electronic Troubleshooting manual. It will show where various electronic relays are located.