So last night I was out riding my recently purchased 1991 K100LT.  I've put on about 250 miles since fixing it up last week.  The bike has been running great, no issues with cold/hot starting, snappy throttle through, smooth acceleration.  I've had no complaints, has been a fun bike to zip around on this past week.

Last night I was out riding and I started playing with the dash light toggle switch, moved it up and down and then I lost power and had to pull over. The light does turn on when in the down position, but is off in both the up and middle position (unsure what up/middle switch positions are supposed to do). 

I haven't been able to get the bike to start as there is no spark to the plugs. I didn't want to dig too deep into before checking here first.

The battery is brand new and at 12.9 volts with lights off. All lights turn on as they should when I turn the ignition on. Voltage with key on is at 12.8, headlights and running lights all on, horn works, no blown fuses (checked continuity). Fuel pump still kicking on when starter button is pressed, starter motor turning engine over. The only thing that seems to be missing is spark. 

Is it just a coincidence that the bike shut off after toggling the dash light switch? Attached a picture of the dash light switch I'm talking about..

One of the major sources of problems with these old machines is dirty electrical connections.  It is why so many of us have a can or two of Deoxit contact cleaner in our tool box and recommend that whenever you get a new bike you go through and shoot EVERY electrical connection and switch. 

As to your question, I have no idea how that light switch relates to your spark problem.  I would start by looking at the green kill switch on the right handlebar, followed by all the electricsl connections between the Hall Sensors on the front of the engine, the ignition control unit and the coils. 

I would also look at the ignition switch.  They are a fairly common source of intermittant engine shutdown.

How did you verify that spark was missing? Were the spark plugs wet? Verify the Jetronic control under the seat is firmly latched then try starting. Verify that the ignition control unit under the tank is firmly latched. Those two connectors could also benefit from the DeoxIT treatment that .75 has mentioned.

Laitch wrote:How did you verify that spark was missing? Were the spark plugs wet? Verify the Jetronic control under the seat is firmly latched then try starting. Verify that the ignition control unit under the tank is firmly latched. Those two connectors could also benefit from the DeoxIT treatment that .75 has mentioned.

Tested with spare spark plug. Yes plugs are wet, engines turns over and fuel pump turns on. 

What do you mean by firmly latched?

RVAThreads wrote:What do you mean by firmly latched?

What I intended to convey is the Jetronic's electrical plug needs to be firmly attached to the Jetronic control. The latch is indicated by #1 in the diagram below. The plug is hooked to the left side of the unit then pressed inward until it is latched firmly to the unit. If it isn't firmly latched, it can disconnect partially or fully; engine performance will be affected.

The ignition control unit can be affected similarly if its plug is loose.

Jetronic control unit.

Laitch wrote:

RVAThreads wrote:What do you mean by firmly latched?

What I intended to convey is the Jetronic's electrical plug needs to be firmly attached to the Jetronic control. The latch is indicated by #1 in the diagram below. The plug is hooked to the left side of the unit then pressed inward until it is latched firmly to the unit. If it isn't firmly latched, it can disconnect partially or fully; engine performance will be affected.

The ignition control unit can be affected similarly if its plug is loose.

Jetronic control unit.

Gotcha - that connection is snug.  I'll try cleaning it with contact cleaner.

In removing my tank, it still continues to drip fuel even when disconnected.

I double checked, I am getting spark at all cylinders... sorry for the misinformation there. That complicated things a bit.

Fuel delivery... I'll have to do a bit more research and these tanks.  

When I put the strainer on the fuel pump there was a nipple for a hose but there no hose there.  Should there be?  Is this a breather? Trying to figure out why my tank drips fuel when lines are disconnected.  

Last night was also the first time I had completely filled the tank, about 5 miles prior to bike dying.

Any help is greatly appreciated!

Fuel filter disconnected.  Hopefully this is the issue.

Edit: Unbelievable.  So the fuel filter works itself loose at the same damn time I toggle the dash light switch.
All good, bikes running!

RVAThreads wrote:When I put the strainer on the fuel pump there was a nipple for a hose but there no hose there.  Should there be?  Is this a breather?

Connecting that is optional. The hose's purpose was to divert air bubbles in agitated fuel from entering the fuel pump by routing it instead to the vapor collector in the tank's ceiling. The filter basket in my Brick's tank has been without that hose connection for 60,000 miles.

If your tank's fuel filter was disconnected from the pump, reconnecting it is good practice, especially if you reconnect it in the correct orientation.

Is it possible to overfill the tank?  Looks like a breather tube at top of tank.  I fueled up on the centerstand and right to the top.  

I've worked on gravity fed tanks with carbs so this is new to me...

following...

RVAThreads wrote:Unbelievable

Exciting!

RVAThreads wrote:Is it possible to overfill the tank?

Sure it's possible but your problem was caused by failure of maintenance inspection. Don't you want to go riding now to celebrate your good fortune?

Laitch wrote:

RVAThreads wrote:Is it possible to overfill the tank?

Sure it's possible but your problem was caused by failure of maintenance inspection. Don't you want to go riding now to celebrate your good fortune?

I want to, but I'm scared too, haha.

I was very lucky last night.  Somewhere stopped and asked if they could come back with their trailer and tow me home!  They wouldn't accept any compensation, they asked me to pay it forward.. on a Saturday night, too.  There are amazing people out there.

Sorry if this is a dumb question but wouldn't the bike still run even with the fuel filter hose being disconnected?

Laitch's Post 10 advises to make sure you have reconnected the fuel filter "in the correct orientation" to the fuel pump. Most manual's show photos/drawings of the fuel filter and fuel pump with connecting fuel line but do not clearly show the inflow and outflow spigot orientation on the fuel filter. Also some fuel filters do not have markings on them to indicate input and output. I know this is 101 stuff, but a simple photo/drawing posted on this forum would be of assistance. Correct filter orientation reduces one more potential problem. Finally is there a simple way of identifying intake and outlet in a fuel filter without orientation markings?

If the filter is unmarked insert a long thin screwdriver into both openings. You will be able to insert the probe further into the outlet than the inlet. Normally the crimped end is the outlet.
Regards Martin.

redrockmania wrote:Correct filter orientation reduces one more potential problem. Also some fuel filters do not have markings on them to indicate input and output. Finally is there a simple way of identifying intake and outlet in a fuel filter without orientation markings?

I haven't encountered a filter without a flow arrow or in/out markings on it, I wouldn't buy or use one without markings. One way to guess would be to blow through the port at each end. The port with the least resistance might be the inlet, but instead, drop obsession with unlikely occurrences and consider shifting obsession to the development of a birdwatching life-list in salubrious fresh air.  Buy a high quality filter that indicates orientation and buy a spare, too.

RVAThreads wrote: wouldn't the bike still run even with the fuel filter hose being disconnected?

If the fuel filter is connected by its inlet to the fuel pump and connected by its outlet to the fuel rail and injectors but you remove it so the pump isn't connected to the fuel rail at all, it won't run well, if at all. Daveyson has run one without a working fuel pump so anything is possible, but he's fearless. 

If the motorcycle is running, take it for a ride. Be fearless! You seem to have enough people skills to help you out of jams while you learn to help yourself. 

Laitch wrote:

redrockmania wrote:Correct filter orientation reduces one more potential problem. Also some fuel filters do not have markings on them to indicate input and output. Finally is there a simple way of identifying intake and outlet in a fuel filter without orientation markings?

I haven't encountered a filter without a flow arrow or in/out markings on it, I wouldn't buy or use one without markings. One way to guess would be to blow through the port at each end. The port with the least resistance might be the inlet, but instead, drop obsession with unlikely occurrences and consider shifting obsession to the development of a birdwatching life-list in salubrious fresh air.  Buy a high quality filter that indicates orientation and buy a spare, too.

RVAThreads wrote: wouldn't the bike still run even with the fuel filter hose being disconnected?

If the fuel filter is connected by its inlet to the fuel pump and connected by its outlet to the fuel rail and injectors but you remove it so the pump isn't connected to the fuel rail at all, it won't run well, if at all. Daveyson has run one without a working fuel pump so anything is possible, but he's fearless. 

If the motorcycle is running, take it for a ride. Be fearless! You seem to have enough people skills to help you out of jams while you learn to help yourself. 

You're right, about to go for a spin.

Thanks everyone!

The injectors are only opened intermittently, and only for a fraction of a second, so gravity fed fuel just isn't enough with the pump removed from the circuit. I got one of mine running without the pump, but the injectors were constantly open in that case. It didn't run well like that, somehow I fixed it without finding out how.

Get a NAPA gold fuel filter #3032.   It's one of the best filters you can buy and it is marked with the flow direction.  Don't use the short hoses that come with it, though, they are not rated for submerged operation.

You can write the month and year on it with a Sharpie pen so at some point in the distant future you will know how long it's been there.

Took the bike out and it died on me again.

The line to the input on the fuel filter keeps popping off.  I put on a tighter clamp so hopefully this will fix the issue. If it pops off again then I'll replace the fuel line. 

The fuel filter was replaced 250 miles ago with the napa gold filter. This was one of the first things I had done as the bike had been sitting for a while and the gas tank was pretty gunked up.

What kind of clamp are you using?  If it's a worm gear screw clamp replace it, it won't hold the hose properly under pressure.  The correct clamp is a 13mm pinch clamp, you should have gotten two of them with the NAPA filter.

Also, did you use the hose sections that came with the filter?  That hose is not correct for use inside the tank.  The outer shell of the hose will soften and the clamps will not hold it onto the filter's hose barbs.  You need hose that is rated for immersion in ethanol.  It is rated SAE 30R10.

757Brick wrote:Took the bike out and it died on me again.

New name, new outlook!  

Congratulation for gambling on a test ride. Remove the fuel lines and check them for obstruction. Replace the lines with SAE30R10 type and replace the clamps with new fuel injection hose clamps like .75 has indicated.

If stalling continues when all parts are well attached, oriented correctly, and there are no fuel line obstructions, don't despair. There is more to check without spending big bucks. This is typical stuff to encounter on a 30-year old motorcycle.

The good news here is that you know the cause of your shutdowns, the better news is that the fix is a relatively simple mechanical one. 

You are close to a well running bike!

Glad I signed up for Geico towing after breaking down the other night, because...

Got towed again last night!

The bike was running great, I was about 4 miles into the ride and I'm waiting at the light... engine was idling great but as soon as I give it gas it stumbled and died on me. Pulled over, had the tools ready to pop that fuel filter line back on there, but it was still connected...

The fuel filter is oriented correctly, napa gold filter arrow facing the direction of flow (the small section of fuel line connected to this end; fuel pump line connected to opposite end).

After it shut down, I was able to start the bike and have it idle but as soon as I give it any gas it would stumble and die. If I was easy with the throttle I could get the RPMS up but not much under load... not enough to ride off. 

Right now, the bike wont idle at all. 

I forgot to mention in this post that the fuel injectors are new, previous injectors were clogged up. 

Does this sound like it could possibly be my fuel pump? I can hear it running, so it's working.. but maybe clogged up some?

757Brick wrote:Glad I signed up for Geico towing after breaking down the other night, because...
Does this sound like it could possibly be . . . 

Congratulations on your prescience!   There are several possibilities; each must be explored in turn.
Did you check the fuel line that goes to the fuel rail for obstructions, or did you replace the line?

Hello, I recently went through these same symptoms. I understand that you replaced the filter but if she was real funky in the tank 250 miles would have been enough to clog the new filter. You may want to have another look at the filter. If it was me I would pull the filter and see if you could still blow through it ( not very tasty). My symptoms were about the same as yours. Worth a try.... And cheap. I had this happen on my boat once. Filter was on the motor for about 2 hours and it clogged up.

Thanks Fishboy - I'm going to get working on it later today, I'm thinking you're onto something here..

I'm thinking Fishboy might be on to something.  If the filter is clogging up, the back pressure could feasibly get high enough to blow the hose from the fuel pump off. 

If there is enough funk in the tank the filter screen may be getting plugged as well.  It's also possible that the filter screen on the fuel pump is letting a lot of crap past it so the pump can send it to the filter to plug it.  It may be a good idea to spend a little time pulling the fuel pump to see if the screen is attached to it properly and doesn't have any holes in it.

So did you get it running properly?

fishboy316 wrote:So did you get it running properly?

Its been running good for a few hundred miles now. Occasionally the pump gets pretty loud. I replaced with another new fuel filter, but really would like to get in there and clean out the tank more... just need to find the time.

That's Great! Time is a precious commodity! Shouldn't take to long to clean it out. I went through something similar but the filter was the first thing I replaced and has been great since. About 1500 miles. Glad to hear she's back up and running.