BMW K100RS 1984 - wierd starting problems

bt952000

Hi all

Just looking for thoughts really, bit of a strange one.

BMW K100RS 1984 - Needs leads replacement with every petrol fill

Background

2016 - Fully service including plugs, fluids, filters etc
Did about 400-ish miles, not much.

2018
Then, bike was laid up for about 2 years until a few weeks back
Charged up ( and filled with de-ionised water ) existing battery, started fine
Got some other work done on it including all new fluids again
Didn’t bother with the plugs as thought they only have 400 miles on them

All good

Took it out for a few spins

Then, accidentally left ignition switch on over weekend
Battery dead
Recharged it
Started
Took it out , stopped it, started it - all ok
Stopped for petrol as ( very low) in misty rainy night
Didn’t have lead replacement with me, put in 5 litres only
Tried to start - tried to kick in but battery died very quickly
Bump started it, got me home

Ok, So the battery is actually dead now I thought
So bought new battery , connected it up
BUT
Still wouldn’t start
All ignition switches lights up, I can hear the fuel pump , but it doesn’t fire up. Just turns

Added Lead replacement , as a long shot

Still the same

Now took out the spark plugs to take a look but they all look ok. No crud, oil build up or caking ( and they are practically new - 400 miles , even though 2 years old )

Tried another bump start but wasn’t having any of it.

So next I will replace these plugs with new ones just as next step but not convinced this is the solution.

Other thoughts

Starter motor maybe?
Rain in petrol tank - but it got me home so that shouldn’t be it.
Fuel pump - but again unlikely as it got me home after the bump start.

What else should I do ?! Any suggestions...

Thanks all

LLewellen Farquarson

First thing is to go to
http://www.k100-forum.com
You'll get lots more K specific advice there.
Second is to tell me your location as there may be an owner nearby who will take a look.
Initial guess is fuel filter (contained in the tank). Was it changed as part of the service?

bt952000

Thanks

Appreciate it

Will post it in that forum too.

Just checked back on service history; the fuel filter wasn't changed then so have no idea when it was ( more than 7 years ago ) but again, mileage over the 7 years is minimal.

In Dublin 6, will look at fuel filter after plugs replacement.

Thanks again.

LLewellen Farquarson

There are a few guys in Dublin who will help thinking of Ringfad in particular. I'd say wait to see what they say before spending money swapping out parts.
Unlikely to be plugs. She would still fire in 1,2,or 3 cylinders. More likely to be fuel related (as you have a new battery)

galwaytt

It's been a while since I worked on them, but from memory. .....

1 - no need for lead replacement. It has nothing to do with start performance.
2 - unless the starter motor turns the engine over a certain rpm, it won't fire anyway. Good battery and starter a must. This is why bump starting is a waste of time.
3 - yes, plugs can cause weird issues. Btdt.
4 - fuel pressure. Having the pump in the tank running doesn't tell you anything about fuel pressure in the fuel rail. That needs to be checked, with ignition on, but also whilst cranking.
5 - It's not unknown for K injectors to stick if left idle for a long time. They're not repairable, so a call to a breakers if they are the cause will be in order
6 - K''s have a load shedding relay which cuts power to all circuits bar what's needed to start the bike whilst the start button is pressed. Check this.
7 - bad earth's. Very common. Double & triple check good earth from frame to engine. Oddball resistance here can result in the fuel pump not running whilst your finger is on the starting button....and so no fuel pressure.
8 - finally - fuel pumps. If K's are left idle they are prone to fail, especially if fuel level is low. They are a 'peristaltic' type pump - not unlike the type you see in a blood bank or dialysis machine: it's a piece if flexible pipe that is "rolled' to push fuel forward. Petrol lubricates it and keeps the plastic pipe supple. If the bike is left idle and fuel level goes low or evaporates, the plastic pipe dries out, goes brittle and may split with full or partial failure. You'll still hear it whirring, but it's doing sfa. If you need to buy a used pump, but double check that the seller kept it immersed in fuel whilst in storage. Buying a used one kept on a dry shelf is just buying the same problem you may already have.....

Sorry for the long winded post !!

bt952000

Hi

Wow, thanks for great post.

Will give this a go but will have to brush up on my electrical skills.

Won't have any time until next weekend now to do anything big anyway.

Might check the earthing (7) tonight if I get a chance and the load shedding relay (6). Looks the same as the horn relay - might just swap them over.

Not sure how I would do 4 but will worry about that later.

5 - It was all working ok and not idle as such as was fine up to stopping for petrol - not sure if that is significant.

8- Might be last resort like 4 above. Will exhaust all others before I go rummaging around inside the tank.

Thanks again for your time writing all this up

Really appreciated

TheBoyConor

if you've ran the engine without the lead replacer you've probably burned the arse out of all the exhaust valve seats. Is there any compression?

bt952000

Eek

Hope not.

I just tried to start it again with hand against exhaust

There was air coming out of exhaust alright though not as forceful as when running but something ; about 30 - 40 % ish

Thanks

bt952000

Also, the trip from petrol station to house was around 5 miles.

Thinking about it , it was 5 euro I put it, not 5 litres without lead replacement

I purposely put is a small amount so not to dilute what was in it too much and get me home.

Just strange it would give up at same time as when I changed the battery.

Really hoping plugs will fix this now ( grasping at straws )

Thanks

Emmersonn

Had a 1988 k100rs and had an intermittant electrical problem with starting. Eventually traced it to a block connector under the seat which was faulty. This block connector was from the fuel pump. All it needed was a clean and a generous application of WD. Never a problem after.

bt952000

Cool, thanks

Will check all the cable connections too while I am at it at the weekend.

two wheels good

You say you can hear the fuel pump. That's good news. It should prime with ignition on, in neutral, side stand up - yes?

Are the spark plugs wet or dry after cranking the engine?
If plugs are dry remove an injector to see if fuel is spraying when engine is cranked.

In addition to galwaytt's good advice on the fuel pump ..
Was the fuel filter changed? They can block/burst.
Fuel hoses in the tank could be perished too. If you have to replace them they should be submersible type not standard hoses from a motor factor.

If the plugs are wet you can have some confidence in fuel supply. Then check for spark at the plugs.
I'd be tempted to drain the tank and add fresh fuel.

bt952000

Thanks all for your contributions

Problem solved!

So checked all the earthing and general cable connections last night.
Everything seemed to be ok.

So went back to basics on what I touched

I then disconnected the ignition control unit and tried to start it out of curiosity, expected nothing. It did the same thing as when it was connected. Took out the ICU from its case, cleaned all connections and left it hanging on LHS knowing the connections were sound, without putting it back in the case.

Boom, started first time. Delighted

Either the connector wasn't sound in the case or dodgy connections but either way, problem solved.

So it looks like it was failing battery and then subsequent introduction of new issue on new battery installation.

Have new plugs in the post so may as well put them in anyway.

Thanks again for all help

TheBoyConor

Glad you got it sorted.
Don't bother putting in the new plugs, you'd be wasting them. The plugs you have have only done 400 miles, they are pretty much brand new. In some engines plugs don't require replacement until 40/50 thousand mile intervals.

galwaytt

Emmersonn wrote: »

Had a 1988 k100rs and had an intermittant electrical problem with starting. Eventually traced it to a block connector under the seat which was faulty. This block connector was from the fuel pump. All it needed was a clean and a generous application of WD. Never a problem after.

True that: forgot that one: the connector to the ECU is 'hooked' in from one end. Sometimes it can look seated.....but possibly isn't. Well worth checking. This is probably what happened here, as it was likely moved when changing the battery etc.

Btw, about the leaded/unleaded: check your VIN number to see on one of the online resources. My 84 ran on unleaded.

bt952000

Emmersonn wrote: »

Had a 1988 k100rs and had an intermittant electrical problem with starting.  Eventually traced it to a block connector under the seat which was faulty.  This block connector was from the fuel pump.  All it needed was a clean and a generous application of WD.  Never a problem after.

Thanks Emmersonn ! The direction I needed