Hey guys,
Sorry that one of my first posts on here is another "Bike wont start" post, I'm sure you're all sick of going through the checklist.
I've read through all the other similar posts and nobody seems to have had the same problem as my bike (a 1987 K100RS).
The problem is that there doesn't seem to be anything wrong!

The symptoms:
When I push the starter button the starter engages, the fuel pump whirrs, the engine turns over and individual cylinders seem to fire occasionally but the bike wont keep running.
This only happens when it is stone cold. When warm she is perfect, one quick stab of the starter button and she is away.
Once running, she purrs like a kitten. No spluttering, backfiring, dead spots in the rev range, nothing.
This has gotten worse over the last few weeks to the point that I can no longer get her started at all.

What I've done so far:
I've been going through the trouble shooting checklist that Crazy Frog wrote (thanks mate, learned heaps about the bike).
I started by stripping her down and going through every electrical connection, cleaning and making sure the contacts are good.
Then I replaced the spark plugs and checked that each of them has a nice fat blue spark.
Then I replaced the fuel filter in case it had sucked in some rubbish.
Then I checked the resistance on the water temperature sensor (3.2KOhms at 15 degrees C - seems about right)
Then I pulled the injectors and each of them is squirting a jet of fuel at the same time, but I'm not sure if it is too much or not enough, I just know they are working!
I managed to get her started yesterday by spraying starter fluid into the air intake and as usual, once she was warm she ran perfectly and started first stab of the button, but today even the starter fluid wont work - she fires up, but wont keep running once the fluid runs out.

I've got air, fuel and a spark.... why wont she run?????? and why only when she's stone cold???
Unfortunately I don't have a fuel pressure tester and I'm a long way from professional help, should I just assume its a fuel pressure problem and replace the pump and regulator on spec?

I'm completely stumped so any advice would be gratefully received!!!!! (sorry for the novel too)
Wombat (Paul).

3.5K ohms at 15 deg C does not sound right to me.
When you measured did you measure from each of the pins to the brass body or directly across the pins.
I ask because that sensor actually has 2 sensors in one housing. One is for the engine temp to go to the ECU and the other is for the fan and temp light.
They both should read 2k ohms measured from each pin to the brass body.
It is 1 quite possible that one can be cactus and the other OK.
The hard starting sounds like maybe it isn't getting the rich signal when its cold. The enrichment comes from 2 places, the sensor and starter button when it is pressed.
Dont go replacing the pump but do replace the filter and to test the fuel flow and pressure, remove the line from filter to pump at the filter. While holding the line in the tank facing down put yur thumb across the hose end and key on press the starter, fuel should squirt past your thumb and spray around the tank, remove the thumb and press the start button again, you should get a realy big gush of fuel. If you can easily block the flow and there is not much flow then look at replacing the pump.
Don't buy an OEM pump have a look at some threads about pump replacement first and buy a good and much cheaper one. You should be able to get one for around $70 max. All thr pump has to do is correct flow and pressure, the Bosch L Jetronic systems are not fussy about brands.

Thanks Rick,
I measured the temp guage across the pins of the plug to the computer as per Bert's troubleshooting guide (pin 10 if I remember correctly).
I'm thinking its a fuel pressure thing, only because when I accidentally left the fuel pipe off the back of the fuel rail - where it goes around to the regulator - and tried to start it, fuel ran out of the fuel rail, but it certainly didn't "Spurt" out like I have heard others mention on this forum.
I'll try your "thumb on the fuel pipe" test and see how it goes.......
If the pump is only delivering low pressure would that explain why it starts and runs fine when hot? I assume the bike needs more fuel to start when cold?
Wombat

O.K, I tried Rick's trick of putting my thumb on the end of the fuel pipe and sure enough, I was easily able to hold back the fuel pressure with my thumb when I pressed the starter.
I tried it again, just to be sure, and again I was easily able to hold back the pressure with my thumb.
Then - just because I'm slightly OCD - I pressed the starter again.
This time the fuel pressure blew my thumb out of the way and sprayed fuel everywhere.
I thought that was pretty odd, but I thought since I know I now have pressure, just for giggles I'll re-attach the line and press the starter...... she fired first go! She ran beautifully without a problem.
So I think I can safely say that the problem was (is?) the fuel pump.
Now, do I go ahead and replace it anyway in case this is an intermittent fault, or did my "pressurizing" the system with my thumb blow out some kind of obstruction that is now clear?
I'll try her again when she's cold tomorrow and in the mean time I'll start scouring the threads for alternative pumps - I just saw the cost of the genuine one!!!
Thanks Rick, you're a legend.

Well it wasn't supposed to be a fix but I'll claim it.
I use a pump from an ED Falcon sedan ( the wagon is different), it's a bit thinner but a few strong zip ties will hold it in place or use the vibration damper for a 94 or later K1100 which is smaller.
You need to change the wire ends from eyes to spade connectors but thats it.
A tip when you take the pump out of the tank there 2 clips that you squeeze in and then lift the assembly up, dont try to undo the small nuts you can see as that way lies total insanity and much skinned hands.
My k1100 I use the falcon pump so that if one fails on the road I can get a replacement quickly and the filter I use one for a VL comodore and it works spot on.

I'm starting to doubt myself now, I keep reading on the forums that if the pump is spinning then its fine and I should look elsewhere for the problem (mine "whirrs" loud and strong)... Is is possible for the pump to be spinning but not producing the required pressure?
Is it possible that the first two times I put my thumb on fuel line the pump was just "priming up" and its working fine?
I have to wait 10 -21 days for delivery of my new pump so I guess I have some time to try other things.....
Oh, I tried her again this morning after leaving her overnight and nope, she wouldn't have a bar of it - would not fire up.
I think I was confusing temperature with pressure though, I think when I leave her overnight the pressure bleeds out of the system and then for some reason the pump can't get it back up to pressure again to start. Whereas when she's been running (warm) there is pressure in the system so she fires up straight away. Just a guess, but it seems to make logical sense... I think...

i guess you could try and clean the pump wombat ...by now youve got nothing to loose ..unless you ride it everyday ...could the non return valve be not seating correctly ? or the roller cells built up some varnish ...taking some while to form a seal ? carbi cleaner would be the choice . not many folks have had success at a dissasembly and reassembly process ...(i guess the damage is already done by that stage )



hope the pump is the fix.... good luck

Wombat wrote:I'm starting to doubt myself now, I keep reading on the forums that if the pump is spinning then its fine and I should look elsewhere for the problem (mine "whirrs" loud and strong)... Is is possible for the pump to be spinning but not producing the required pressure?
Is it possible that the first two times I put my thumb on fuel line the pump was just "priming up" and its working fine?
I have to wait 10 -21 days for delivery of my new pump so I guess I have some time to try other things.....
Oh, I tried her again this morning after leaving her overnight and nope, she wouldn't have a bar of it - would not fire up.
I think I was confusing temperature with pressure though, I think when I leave her overnight the pressure bleeds out of the system and then for some reason the pump can't get it back up to pressure again to start. Whereas when she's been running (warm) there is pressure in the system so she fires up straight away. Just a guess, but it seems to make logical sense... I think...

what you say about priming is possible. i had a pump go a while back and it was running very eraticly and while it was cutting in and out quickly the bike would still run but then it would stop for a few seconds and the bike would stop. i think it had a bad internal connection.
you could try pressing the start button six or so times before trying to start to see if it builds pressure.

Hi, I had a fuel pump idn my k75 that had a bad back flow valve so it would loose pressure overnight, then it would take a bit to get her to start, put in new pump , fires right off.

Seems to me that there is a sort of spares kit every K bike owner should have in his bike house:

Spare fuel pump.

Fuel filter.

Injector.

Fule pipe.

Starter relay.

Load shed relay.

Starter motor brush replacement kit.

Temperature sensor.

Spare main stand.

Spare ignition control unit [under headstock].

Any more we should add to the list?

yep pretty much the first 7

dont forget

spare fuses

spare ignition lead

spare plug or 2

and a couple of hose clips

and some drie bond

fence pliers are an optional extra ..... there lots of fences made of wire here in aus (giggles ) a "bushie" can do amazing things with them fence pliers