Brought the bike as a winter hack (very cheaply)...
The guy claimed he had just replaced the fuel pump, but I wouldn't trust his word on that, after the state of the bike...
It ran, as I rode it home..
Fixed head bearings (grease had solidified) and rear brake (seal gone)...

But since, the sprag starter keeps letting go... I've put in some diesel Turbo oil to try to clean the sprag, hopefully without having to strip it...
Sprag doesn't correct with wheeling backwards in gear... it is better after being stood but after a few tries it returns to just letting go...then every 3rd or 4th try sticks long enough to get the motor trying to start...

BUT it just wont start, it wants to, if I can get the sprag to stick.. it runs for a short period (just a few seconds) then dies.

Similarly if I try to open the throttle, to get it to run, it dies...

I managed to get it started a while back and ran it for half an hour, (under virus lock down so no riding), it ran rich, but it ran.
Although I had to start it on the choke, even though 23 °C....

Strangely the gear indicator LCD, has gone from a nice font, to as if the LCD is bleeding , so the gear numbers are blotchy, as if written on blotting paper..

Could this be the pressure regulator ?  Somewhere here I read you can remove the vacuum connection and it will run ok ?

I don't want to spend loads on this, swapping parts in & out, to get a fix...
I have other bikes, so could do with the room , if this is a bust, will just sell for parts... I was hoping to just have a nice winter hack...

I am not confident electrically, I have a volt meter, so can check continuity, voltage etc, but nothing technical...
Any idea ?
Cheers

Hi Noisey,,

It will help to know which model you have got.

Mike

Sorry - being a dumb ass...

K100 1987 model...

fully faired, square headlamp.

Have you seen the troubleshooting guide? It can be found on the Portal page 
http://www.kforum-tech.com/ A good bit of reading while in lockdown 

Ignoring for the time being the sprag issue affecting the ability to turn the bike over, an easy check is the resistance of the water temperature sender (2.5k ohms at 25C, 300 ohms at 80C). If there is corrosion on the joint to the engine or if the sender is open circuit it will cause an over rich mixture. This in turn can kill the spark plugs, exacerbating the fault finding procedure. Note where the measurement is taken - from the EFI female connector, once it has been removed from the module.

I take it you are aware that the 'choke' control just opens the throttle a predetermined amount, that the ECU uses to set the mixture.

I'm sure others will chip in.

Mike

Cheers - I think..

I have just done a search in the on line manual and can't find EFI ( refili - seems to count as EFI by pdf search)

Searched google and I got the fuel filter ...

So what is an EFI and where is it on the bike ?

I've just done a similar search on the temp sensor - it's not clear where it is, but some where on the barrels, so I should be able to find it ...

I had a look at the trouble shooting guide but....it covers everything, so a bit daunting when I have no idea where anything is on these bikes.

Yes I know the choke is just an increasing idle increaser - BUT you shouldn't need that surely when the outside temp is 20 to 23°C, which maybe the temp sensor has gone...  

Maybe it was just luck that it has run...

EFI: Electronic Fuel Injection, in this case it's Bosch L-Jetronic if you're talking about an 8V K100 or K75. The flapper unit is inside the airbox under the air filter. Generally they're dead reliable.

Put the year and model info in the signature line of your profile so we are not guessing or having to read back pages to see if the info is there.

There is a temp sensor on the combi water/oil pump that measures the coolant temp for the gauge, then the fuel injection water temp sensor is on the water stub, LF forward top of engine behind radiator. Not easy to get to in a quickie.

The 'choke' on my RS is often needed for half a minute (or less) to start initially, regardless of ambient air temp. If the bike is warm from being run previously it's not needed.

The fuel injection control unit is in the under seat area. You will need a small screwdriver to release the locking catch to enable you to remove the connector plug.

Mike

First question; Is the fuelpump running?

Right...after a few attempts...

So with my meter set to 20k Ohms...
Temp Sensor..
EFI Pin 10 to earth = 2.9 = I assume that is 2900 Ohms (which at a little less at 20°C, maybe 18 - 19, seems right)

Air flow meter..
Pin 7 - 5 = 0.106 = 106 ohms ?
Pin 7 - 8 = 0.362 = 362 ohms ?
Pin 8 - 5 = 0.362 = 362 ohms ?
Now it says in the trouble shooting guide...
"...If you are checking the airflow meter at the injection computer plug, it must be done with the fuel tank electrics unplugged.  Otherwise pin 9 is earthed via the fuel pump and all the readings between pins 5-7-8-9 are wrong. ….."
I was unable to find the fuel tank plug - so will need to try again tomorrow by actually lifting tank, not enough time tonight..

Air Temp Sensor
Pins 8 & 9 = 0.202 = 202 Ohms ?

Yes, I think Fuel pump is working, as even when trying to reverse bump to losen sprag or bump start, you can hear the pump run, same as with starter button / ignition on..
Previous owner claimed to have replaced fuel pump, which could be just sales pitch as it also came with an MOT... whilst the head race bearings were solid and rear brake not working... so I wouldn't bet on it..


BMW 1984 K100 RT

OK, 2nd go..
The only electric cables from the tank I could find, was a 4 female pin round socket, adjacent to the front petrol down pipe to the injector rack.
So that was disconnected...

So meter set again to 20k
Temp sensor, warmer this evening 22°C in the house (bike in garage mind you) and the sensor reading reflects this...
Pins 10 to earth = 2.76 = 2760 ohms

Pins 7 to 5 = 0.107 = 107 ohms

Pins 7 to 8 = 0.363 = 363 ohms

Pins 8 to 5 = 0.362 = 362 ohms

Pins 8 - 9 = 0.200 = 200 ohms

So based on those values...There isn't really much difference from the previous nights readings, so disconnecting the tank electrics hasn't made any difference ??
But it seems that :
a) Water temp sensor works...
b) air flow works, although the pins 7 to 5 reading is high compared to the tech page..
c) Air temp also seems to be in the right range for the temp...

So where to now ?...

With the fuel cap opened, or better removed,  check to see fuel returning into the tank. Have a bit of a look to see that everything is in order.

Hi Noisey
I always was told to look for the easy solution first by these guys. Is the fuel filter fitted the right way round? has an arrow indicating flow if it's a BMW part.
Good luck
RT

Thanks guys, but as the bike was ridden home (15 miles or so) and I've not touched the tank, I don't think these could be the issue.
It has started since, albeit with what sounded like rich running but no tickover…  Petrol is getting to the spark plugs.

I am thinking more along the lines of :

a) possibly something has given up the ghost and I was just unlucky enough to have it run, long enough for me to buy...
or
b) something has just gone (the bleed effect on the LCD display suggest this).
or
c) I effected something in stripping the front end down and sort out the rear brake to fix... Luckily I only have the top / headlight part of the fairing on, so not too much to take off.

 Or...… any ideas ?

Neil

I have an intermittent problem with my engine misfire, it is the EFI, the wire going to it is pressed against the frame and it has a tight bend , the wires are old and brittle, they can sometimes short.  Check that you have all the plugs seated properly, the plug for the fuel tank is a week spot.

It's hard to eliminate causes, if you don't reply to them. It's only four screws to remove the cap. Spose the owner did replace the pump and a hose popped off after you got home, or disturbed gunk caused a blockage. Is the filter the right way around? Is fuel returning to the tank?

I'm having the same problem, hope you get the problem sorted out sometime soon.