My bike died on me a month ago and while it still starts very easily, it only runs for maybe 2 minutes at best and then dies.  it will start again immediately but it then dies again.  Since the fuel pump was getting to be noisy, I started there and bought a new Bosch pump and filter.  This wasn't the problem.  I have now changed the Hall Effect Sensor and I still have the same issue--easy start and then dies after a minute or two.  I used a special anti-oxidation electrical contact cleaner on the computer hook up, so I am confident that the connection is good.  I don't really want to just keep changing parts, but I'm starting to suspect the coils.  Do my symptoms point to this?  I do believe they are original to the bike and I'll looking at 100K miles on it now.

Any advice?

Start telling what bike you have (K, but wich one? )

hah,  1985 k100RS  Sorry!

@jumpinjimmy wrote:hah,  1985 k100RS  Sorry!

Hi Jumpinjimmy, 88 and myself have been down your way last 2 years. Camped at St Leon sur Vezere. Lovely area and am hoping to get down in September.

I am not sure both coils would fail at the same time but am open to correction on it. Does the engine do a clean cut out or will it struggle to run on 2 cylinders?

Wondering could there be an issue at the fuel pressure regulator.

But before looking at that have a close look at the electrical 4 pin connector to the fuel tank. This is a known problem area and I have suffered the same issue. This should be a snug mechanical fit.

This sounds very much like a fuel filter problem. You say you changed the filter but was it the filter at the base of the pump or the inline filterinside the tank after the pump?

The filter inside the tank and also the filter at the bottom of the pump were cleaned and weren't that dirty anyway.  I had already changed the in-tank filter in 2014 but went ahead and changed it again as a precaution since I was in there working.  The tank is very clean on the inside and the pump strainer/filter was virtually without debris.  Anyway, the shutting down is pretty clean... it stumbles, loses power and then dies and does not seem to be running on just two cylinders but all four.  It will always fire right up again, but run for a shorter length of time as opposed to a complete cold start, in which case is runs for about 2 minutes max.

If its running on all four but badly it seems to point to something shared between all 4 cylinders. If its running for just about 2 minutes I am wondering is it a case that fuel pressure is dropping, as the guys are saying [due to fuel filter or pump issue] or is power supply to the fuel pump interrupted or not present after the initial start up ? The fact that it turns over rules out a lot of other potential suspects.

I must admit that although you have checked the plug onto the Fuel Injection Control Unit I have found quite a few locally here that this was compromised when it was all put back in place although it looked perfect and the connections had been cleaned. We ran a K75 with the FICU just hanging off the plug and the problem disappeared.

I don't think it's a pump or filter issue as both of these components are new and I can clearly hear the pump turn if I bump the starter button.  Where is the four pin connector you mention?  Inside the tank?

Also, at start up, it's running great, not badly!  Runs perfectly!  but after a few minutes, it starts to lose power then just shuts down.  I'm pretty certain I've got the multi pin connector to the computer connected properly.

Being all 4 cylinders, I think Rick G is on the right track, being a fuel problem. If you are able to put a pressure gauge on the pressure fuel line, not the return line, and watch what happens you might get some enlightenment.

Bill

@jumpinjimmy wrote:I don't think it's a pump or filter issue as both of these components are new and I can clearly hear the pump turn if I bump the starter button.  Where is the four pin connector you mention?  Inside the tank?

If your tank is bolted down this 4 pin connector is underneath the tank at the front left of the tank. It unplugs and you will see if it is burnt or overheated from shorting due to poor connections.

If your tank is not bolted it will be at underneath at the rear of the tank, on the right. No need to remove the tank in either case to access it.

My K100LT was modified by a previous owner as this plug had failed, seemed quite easy and I had 4 separate spade connectors.

I will check the pin connector.  My tank is bolted down and I've seen this thing on the front left side of the tank.  I've already done the fuel pressure test which is what made me decide to change the pump (outside the fact that it was an original part and very noisy).  There was too much pressure which indicated the relief valve was not working properly.

The pump operates I think at 60psi but the fuel pressure regulator reduces it to 36psi.

The electrical plug should be a nice snug fit, not a loose fit. You can prise open the pins on it and squeeze up the female connectors to make the electrical connections tighter.

wish I could post a video here.  I've filmed what goes on.  In light of the fact that it runs perfectly and then shuts down, I'm leaning towards a fuel delivery problem but I feel as thought the pump and filter are not the problem.

Just a thought, try running the bike with the fuel cap open. You should have a steady stream of fuel flowing back into the tank. Check if that is still occurring as it cuts out. If its simply blowing air instead of fuel you might have a pick up problem, means the fuel rail is not getting enough fuel to pressurise and stay running. Having been at one recently we had to put 5 litres in from empty after replacement of pump, filter etc to get it all to run right. My own experience is that a 22 litre tank is only good for 18-19 litres, the last 3-4 litres don't seem to come out.

As you say a fuel delivery problem is highly likely. May be a case of rechecking the fuel line connections inside the tank are all ok, but check the connector outside the tank first simply because it's less messy.

@jumpinjimmy wrote:......I've already done the fuel pressure test which is what made me decide to change the pump (outside the fact that it was an original part and very noisy).  There was too much pressure which indicated the relief valve was not working properly.

Where were you measuring and what pressure were you getting?
If you were getting too much pressure its possible the fuel pressure regulator is faulty. Check the fuel return hose at the front/left under the tank. It comes from the FPR. Disconnect it and stick in a 2 litre coke bottle. You should get a good steady flow. The flow from the rear hose to the fuel rail should gush out.

Re video... upload to Youtube and use the Youtube button on the tool bar.

@Holister wrote: Check the fuel return hose at the front/left under the tank. It comes from the FPR. Disconnect it and stick in a 2 litre coke bottle.

But take care when removing the hose, if the return valve is modified
(not unusual, to stop the annoying rattle from the valve) you gonna get
a steady flow of fuel out of the spigot until the tank is empty.

I used the test outlined in this PDF for testing the pump and according to this article it was the relief valve in the pump that was bad.

http://tomwade.me/motorcycles/technical/k100troubleshooting.pdf

a good point!  I'm going to look again, but I checked and there didn't seem to be the usual disturbance from the return fuel in the tank.

Here's a video link to my bike starting and dying.

https://youtu.be/hTzHcXRZIDY

What is the condition of the spark plugs--are they dark, wet and sooty, or light and dry?

After you put them back in, are you able to get the revs to raise by quickly chopping the throttle?

My guess is that it is related to temperature such as either the air flow or engine water temperature sensor, or the fuel pressure regulator, but it depends upon the spark plug condition.

Your engine is starved of fuel. Even when its running, it sounds like its not getting enough fuel. When the motor does die, you can hear the fuel pump running for a couple of secs. That's priming the lines again and why it'll start again straight away. So if you are sure you're getting 60psi at the pump then it must be the FPR imo

@jumpinjimmy wrote:I used the test outlined in this PDF for testing the pump and according to this article it was the relief valve in the pump that was bad.

http://tomwade.me/motorcycles/technical/k100troubleshooting.pdf

For clarity, are you referring to the test on the last page or the second last?
The second last page is the definitive one IMHO.

Bill

I'm using the test from the very last entry on this pdf.  It's the very last photo and shows the gauge connected directly to the fuel tank/pump outlet.

Thanks for the quick response. If you can do the second last page test, and report the results as the engine starts, runs and stops I suspect the solution will become clear, and Holister's suggestion seems likely. 

Bill

yes, FPR does seem logical now.  I do wonder why it can run for longer when starting from dead cold.

If it is starved then the plugs would be dry, but if flooded then wet plugs.

If the FPR fails closed due to leaking vacuum tube then the rail pressure will be too high, which will cause a rich mixture condition (flooding/wet plugs).

Even bypassing the FPR completely (fails open) a k bike will run.

The main culprits to produce a lean mixture (dry plugs) are air leaks, or defective temperature sensors, rusty fuel rail and clogged injectors/screens, or a defective jetronic.

I would have noticed black smoke if there would have been a flooding situation, so I'm doubting that.  Haven't pulled the plugs yet to inspect them but I would bet they're not wet after shutting down.

Jumpinjimmy, check moving wires and contacts. For example wires from right hand switch which connects under the tank.
I had the same symptoms and problem was loose contact from RHS to connector under tank.

If it would rev up by chopping the throttle quickly then i guess they will be wet, but if not then dry.

Was this bike a daily rider that suddenly experienced this, or has it set up for some time without starting?

I started it today to see what would happen and it ran really well for a solid 5 minutes and then just died.  I revved it up a few times and it took the gas just as it should and then suddenly pooped out.  I started it immediately again and it ran for a little bit then died.  I'm baffled.

Next time can you run it like that with gas tank open and see how it keeps circulating the fuel back into the tank. Let us know if the fuel coming back to the tank stops before the engine dies or after.

To reply to an earlier question, this bike was ridden regularly for the past 2 years but prior to that it had been sitting for years.  I recently made a 500 mile trip and the bike ran beautifully.

I did look in the tank and could see fuel being returned but I didn't wait to see if it stopped before the engine died.  I will try that today.

Thanks everyone!  I'm hoping to get to the bottom of this soon as I really want to RIDE!

I've never been a believer in the method of repairing something where if you look at it long enough, it will fix itself, but that said, I started my K bike yesterday and it ran fine and didn't shut down.  The only thing I have done to it was to re-position the filter in the gas tank a little bit because I thought the 180 degree bend looked a little too extreme and I was worried that it could be cutting fuel supply.  I can't believe this was the issue all along.

Not knowing the real issue has shaken my confidence in my wonderful k bike.

@jumpinjimmy wrote:I used the test outlined in this PDF for testing the pump and according to this article it was the relief valve in the pump that was bad.

http://tomwade.me/motorcycles/technical/k100troubleshooting.pdf

It would've been useful to know what pressure you got with this test. It may have explained a kinked fuel line in the tank.
Good to hear its sorted and back on the road.

You could always reposition the pump so the line is kinked again and see if the problem returns.

Mike

Well, I'm feeling pretty frustrated at the moment.  I was confident that my bike was running well now...I could start it and run it until the cooling fan would kick in and no sign of any issues losing power.  Prior to this, the maximum I could run it without it shutting down was just a few minutes.

So thus far, I've changed the pump, filter, hall senor and cleaned all electrical contacts on the bike that were accessible under and around the tank (also took the time to change all of the old fuel lines). 

Today I took it for a test run...no problems.  Drove for 10 miles to the nearest town, had a coffee.  Started off again, went and filled up with gas and then while paying at the kiosk, it shut down.  As usual, it will always restart and I can hear the fuel pump, but it would only run for half a minute. 

UGH!  Any ideas???   Having just filled up with gas, I wondered if the vent was plugged, but I opened the gas cap and tried running it to no avail.

Relay?

Good Luck to ya--folks who have fixed and solved many bike problems have given you free advice based upon their wisdom and experience, and only asked in return just some basic test results and feedback, yet you have ignored it all...

Does it ever let out a ripping big backfire, if so clean the ignition switch, not the key lock but the contacts below.

It is very unusual for a blocked breather to have any effect on a Fuel Injected system because it does not rely on a gravity feed to get the fuel to the injectors.

I have also had vapor locks in the fuel system because of very hot wheather and had to fit a small cooler radiator in front of the main radiator that cools the fuel as it returns to the tank. I did get a very hot day here last year that caused a few unexpected stops due to boiling fuel. The fuel was so hot it burned my hand while I was changing the fuel pump as I thought it was the problem to start with.

Has there been movement inside the tank, causing the pipe to be kinked again?

Mike

Check your valve clearances

Thanks for the responses.  Never backfires and it always!! starts right up...even now with this problem.  Check valve clearances??  I'm afraid you'll have to explain the reasoning before I venture down that road.

When you try to start the K and it wont start do it with fuel tank open and see if it's pumping fuel back into the tank.

@jumpinjimmy wrote:Thanks for the responses.  Never backfires and it always!! starts right up...even now with this problem.  Check valve clearances??  I'm afraid you'll have to explain the reasoning before I venture down that road.

Its not a hard road to venture down. Very easy to do.

1. Remove the camshaft cover.
   
2. Remove SPs so you can turn it over easily.
   
3. Turn the motor over (19mm spanner on the top camshaft) so the back of each cam is aligned to the shim/bucket.
   
4. Test the gap with a feeler gauge.
   

Specs are in the manual. Sear.ch Chris Harris on Youtube

If they're out, particularly the exhaust valves, the engine won't run as well when throttle is off/closed.
When the engine warms up the gaps get tighter and effect the performance even more. It can cause the engine to stall.

When you're running out of ideas, this would be my next 'best guess'.
Cheers

Thanks Holister, I'm more inclined to think it's a fuel starvation issue but I must admit that I haven't adjusted the valves in ages, so it's time to do that!  I'm going to go and collect the bike this morning at the garage where I left it yesterday and see what's up with it.  Something is really amiss when my 1977 Harley Electra Glide is more reliable than my brick.

Check the condition of the SPs right after she stalls

Must have caught something from the Harley

Any chance you could take a couple of pics of the inside of your tank?
And the outside connections to the fuel rail

Well, just spent the last two hours having breakdown assistance pick me up.  They're the greatest here in France.  Front door delivery.  Ran perfectly for about 5 miles then just shut down.  As usual, would start right up again but then die after a few seconds.  Once cooled off and unloaded from the flatbed, I was able to drive it right up the hill to my garage with no problems.

The coils are original equipment and I have had the experience on cars of coils playing up once hot.  Any thoughts?

Those original coils are well known for doing that too......just like your experience in cars. Its a good move anyway to change them.

But both coils giving out at the same time doesn't seem likely. However I don't see the K running too well on just one coil.

Still never really worked out if its fuel supply being disrupted or the ignition side being disrupted. Check when it happens again by opening fuel tank and seeing if the fuel is being pumped back into the tank while you have the starter engaged. No fuel means it's not the coils and you should be looking on ignition control side and fuel supply side. There have been instances of poor connections to the electrical fuel pump plug under the front left of the tank causing this cut out and I have been there with it. The wires can even become detached from the metal pins.