Hi All

got a wierd one? K100 RT 1984

When I thumb the starter to start up the bike, the starter motor cranks momentarily and then nothing while still holding the starter button.

the fuel pump primes as it should- i can hear it.

if i repeat the process the same happens?

i got the bike to start- on one "kick" , but it did the same again after trying again.

Battery is good so i can safely rule that out-
checked all my main earth connection and positive connections to the batter , starter and on the engine - all good?

my thinking is perhaps the relay?  does these bikes have one andif so where abouts is it located on the relay box.

many thanks

The relay is the one in the rear right hand corner as you stand on the left side of the bike with the seat up and the tank raised enough to get the lid off the elec. box
Do you hear any sound when pushing the button ?
I have had a few K100 just spin the starter & the sprag clutch will not spin the motor.
spag clutch slipping.
May need removing & cleaning, a big job.

Hope that helps
PJ

thank you will have a look at the relay

no not the sprag clutch as what is happening is that the starter kicks on and the engine cranks say 1 revolution and then the starter disengages and will not continue cranking- starter doesnot run free

its almost like if one was to image that you are doing valve clearences and you are touch touch the starter so as to turn the motor over one step at a time so as to get the cam lobes in the correct position to set the valve clearence.

It could be a starter relay coil grounding problem, the coil grounds via the ignition ECU.
Try a tempory ground wire at the relay connection to verify.

It also relies on the hall sensor signal to the ignition ECU to function correct,
With a bad hall sensor the starter would go on-off-on-off-on-off, while pressing
the button.

Rene Z got a story about this, search the forum..........

I had a similar problem with my K100LT and I think IngeK is correct about the grounding through the ECU. I went through everything else, swapped relays etc until only the ECU was left. I took it out, cleaned all the connections earths everything. Problem persisted. BMW wanted €75 to test the ECU. I gambled and got a used one from Motorworks for about £50 and it cured the problem. I still don't know if it was the connection to the ECU or the ECU itself but the problem was cured.

do you find that it will start /almost start on first attempt and nothing after that?
as you release the button can you hear the fuel pump activating .
If you were to remove the fuel hose from the filter or fuel rail and feel fuel under pressure as you release the starter button ......... check the fuel injection relay .
this may help to locate your FI relay, it is the small black relay , which can be found in various spots on the right hand rear box area.
the horn relay on some K's can be substituted to help diagnose.
good luck.
for the preservation of your sanity , please start at #52 in the postings. otherwise enjoy the madness.
be sure to check all connections for earthing and conductivity ( clean and deoxit ).

Thanks chaps will have a look

Mr Inge- I did have an occassion where the bike struggled to start after waiting for my friend riding with me to catch up- what happened in this instance is that it would crank crank crank but no fire up. The bike was not hot as it was as I left home in the early morning. strangly enough it never did this again though.

can this be a sign of the hall sensors starting to give me trouble?

Grover K sent you to a good post.

I started out by cleaning and tightening up all the connections, remaking some earths etc.
Swapped starter relay.
Swapped load shed relay.
Swapped other relays around.
Stripped and cleaned starter motor [quite easy but just be careful to do it right]

Still no joy.

Took out ECU and cleaned all connections. Opened it up and it was like new inside.

88KE offered to swap ECUs but when I looked at the cost of posting decided to just get one as it was now top of my suspect list.

The 'new' ECU ran just fine.

With what I know now from the forum I understand the operation of the K much better. It seems the ECU controls the earthing so if power is getting in to the switches then the trouble should be down the track from that, as in its not earthing. I may be wrong but I think the ECU also controls the earthing of the relays [fuel pump starter, load shed]. If you are getting the starter to at least work, the fuel pump to at least work then it would seem to suggest the relays are working but not getting signal at the correct time. Hopefully someone will confirm if I am right or wrong in that.

yes he did- reading through it all now.

oh boy I am going to have to learn electrics- have always been scared of them!

A word of advice, when it comes to connections do them one at a time. Never open up a load of them, be patient and go individually.

Due to age of bikes some previous owners may have made changes to you may not exactly match the wiring diagrams.

There is a quite a lot of wiring under the petrol tank but you should be able to trace the connections from the right hand switch unit as well. The connectors need to have some degree of tightness to make a decent electrical connection so if some of them are barely together you may need to crimp them up slightly to increase the interference and the electrical connection. I would check all the connections and earths before buying any parts or relays, there is a big one under the tank and one on gearbox above the gear level spindle, others may be scattered in there.

There is a multi pin connector to the ECU that should be cleaned off. Getting the EUC out is easier than it seems, the two fixings don't have to be removed as the plates which are bolted down are slotted so it will pull clear. The onnector can be cleaned off with a folded over dry 1200 grade wet and dry until its nice and brass shiny!. Very important when you are done is to make sure all the baffles and heat protection are put back correctly.

I just noted you have a 1984.

For what its worth I also had a problem with the electrical plug in connector at the front left of the tank on the 84 RT. Its a 4 pin male/female that plugs into a socket on the underside of the tank up near the front. You have to take off the fairing leg inner and the storage box and baffle underneath to get at it but they are quick to remove.

If I remember correctly the male pins are in the plug that you pull off the tank. Mine was a very loose fit and it did what you described. Very gently prise the male pins to open them out very slightly and see if that takes it a tight interference fit.

What happened with my RT was that the starter would turn over no problem, but because the electrical connection at the tank plug was broken there was no fuel being pumped, it was as if no petrol. I recall a post that the fuel pump gets a signal when you press the starter, but when the starter is released and engine running the signal to the fuel pump comes from a different source. A few I spoke to said that connector can have problems.

RSMITH wrote:Mr Inge- I did have an occassion where the bike struggled to start after waiting for my friend riding with me to catch up- what happened in this instance is that it would crank crank crank but no fire up. The bike was not hot as it was as I left home in the early morning. strangly enough it never did this again though.

can this be a sign of the hall sensors starting to give me trouble?

It could be a hall sensor problem.......but also open for a lot other posibillities here.

The easiest would be to check with a temporary relay coil ground, if the starter runs OK it's ignition the ECU or the hall sensor(s) that is the problem.

In thread about hall sensors yesterday you find some links where you find how
make Your own hall sensor tester (also at troubleshooting guide at the portal).

Thank you all

dunno what to do?  now starter is swinging over as normal  and bike starting up everytime! I didnt do anything other than try it out before checking the electrical connector plugs

I am still going to carry on and do clean up of all the connectors and do as you say Inge , make up a ground for the relay ect as I dont really want to get stuck in  the heat in the bush 120km from "Gat Zonder Water" on a sunday afternoon with no one except  bleddy flies for company.