So the Bike and what works:

1. BMW K100 RS 1985 (Modified as a Cafe racer by previous owner, so hacked to bits)
   
2. Bike was running fine before Winter (UK)
   
3. I had the tank off and changed spark plugs over winter, never tried to start it
   
4. Connected it all back up and it won't start
   
5. Checked side fuses, all okay
   
6. Checked the new spark plugs, all sparking
   
7. Checked the fuel pump and injectors all working fine, spraying okay when turns over.
   
8. Engine cranks around on starter
   
9. Battery is fine
   
10. Top frame Earth is good (I cleaned it up again anyway)
    
11. The bike is getting air(i hope , as how would it not?)
    

I've cranked i over for quite a few battery runs and it never FIRES it just cranks on and on. BUT when I removed all the injectors to see if they were spraying the bike DID fire up for a couple of seconds. What?????

What on earth am I missing here, it has spark, fuel and air, surely it should FIRE over now right?

Have I flooded it beyond good or what? 
Is it a sensor thing? 

Could some bright spark please help me?

Kind regards,
Jon

Are the spark plugs wet or dry? If wet remove the Fuel Pump ( Kraffstoppe) fuse #6, and try to start it. It should run on the residual fuel in the combustion chamber. If it still floods after replacing the fuse check the temperature sensor connection and the sensor.
Regards Martin.

Check the fuel pump plug (at the rear of the fuel tank on the right hand side) - you wouldn’t be the first not to plug it back in after the tank has gone back on. If it is plugged in, various forum members have previously had issues with poor connection due to the sockets splaying out and not making a good electrical contact.

Trouble with cafe hacks is you can never be quite sure what things have been removed, so trouble shooting is that much harder. Always start with the obvious though.

Thanks for your advice guys,

The plugs looked a bit wet but not dripping if that's a thing. The bike had pretty low compression before winter when I last did a test, so after whating a youtube video on K bikes the advice is to put 10cc's of motor oil in each cylinder to regain compression and get it starting again. As after a long sit over winter they can lose more compresion.

I'm really crap with electrical stuff but I have a mulimeter and love learning so I'll try your suggestions. 

I'll update tomorrow hopefully!

Thanks,
Jon

MartinW wrote:Are the spark plugs wet or dry? If wet remove the Fuel Pump ( Kraffstoppe) fuse #6, and try to start it. It should run on the residual fuel in the combustion chamber. If it still floods after replacing the fuse check the temperature sensor connection and the sensor.
Regards Martin.

Hi Martin,

Would you be able to explain the relationship between the temp sensors and the bike starting? 

Thanks,
Jon

oil in the bores as per you tube video is the best guess

moriarti wrote:oil in the bores as per you tube video is the best guess

Will report back sir.

Moriarti, if you're in Yorkshire do you ever get down Squires Cafe??

The temperature sensor sends information to the computer. If the sensor or it's connection is faulty the computer over enrichens the mixture causing flooding. If you can get it to run with the fuse out with a bit of throttle manipulation. Then as the engine dies you can if your quick enough jam the fuse back home, and keep it running by playing with the throttle. A faulty connection has caught me out twice in 20+ years and I've managed to limp home doing this. On the way home the connection came god and it ran normally. The sensor is positioned so it cops a fair bit of road spray (salt) and crap. I eventually chose to thoroughly clean the connection and waterproof it with thick silicone grease, it's been fine since.
Regards Martin.

Im based in Brighouse and yes i get over to the cafe 
i even take my own pork pies with me 

My 1984 doesn't have the 2 part temp sensor and i would think yours doesn't ether if so life has become so much simpler.Post your bike details to help members with their answers inc vin number

So I fully charged the battery and added a little engine oil inside each cylinder to make better compression, and no start still. I might do a compression test next.

As mentioned before, the only time it started (during this diagnosis project) is when I removed all 4 Injectors, any guesses as to why this might have worked? 

During last Summer it was running fine starting up on first hit of the button, I then did some clean up work over winter, removing the tank, changing the spark plugs and did some frame painting work. I havent done anything major or extreme.

Any suggestions on a logical step by step to diagnose further? 

One thought I have is the Injectrs were spraying but I'm not sure if it was powerful enough, so it may be the pump. But the pump does run when you press the start button. And there is defintely spark. Could Air be an issue, if so how?

Thanks guys

After failing to start are the spark plugs wet or dry??
Regards Martin.

What is the battery's output when it's under load? The battery might be too weak to get it started.

MartinW wrote:After failing to start are the spark plugs wet or dry??
Regards Martin.

With my limited experience I'd say they are dry, they certainly didnt look like they were covered in fuel. I'm starting to think even though everything is working, there may not be enough power from the battery as suggested. I'll check the battery under load tomorrow.I also have another bike so I may swap batteries and see if that fixes.

Laitch wrote:What is the battery's output when it's under load? The battery might be too weak to get it started.

Not sure, Im going to check the battery tomorrow with my multimeter and also swap it for another I have

clnl_hrkr wrote:Thanks for your advice guys,

The plugs looked a bit wet but not dripping if that's a thing. The bike had pretty low compression before winter when I last did a test, so after whating a youtube video on K bikes the advice is to put 10cc's of motor oil in each cylinder to regain compression and get it starting again. As after a long sit over winter they can lose more compresion.

Don't trust what you can see on Youtube.
Winter does not lower compression.
Wear does.

Pouring oil the combustion chamber is a good thing only if you intend to measure compression, because it's supposed to temporary seal the piston/cylinder junction and allows to compare with a previous measure without oil to validate or not if the low compression is due to worn segments or leaking seat valves. Or valves under permanent constraint, but of course, you have previously checked this before, don't you?
Note: this method only apply to vertical cylinders as long as you're on the earth.
In other cases, if you live in interstellar location or if your motorcycle is a K bike with horizontal cylinders, the only consequence of pouring oil in the cylinder will be to kill your plugs -and eventually your engine as oil is uncompressible. Connecting rods are.

Buy new plugs, seriously clean your tank, buy new fuel, check that the 4 injectors are spitting the correct amount of oil during 1 minute (be careful, no erratic spark during this test...) use a big car battery shunt on your bike, a low amp. battery won't deliver enough to start your engine, particularly if the starter has to cope with 4 cylinders full of oil besides having to deal with demanding fuel pump and an ignition system which turns to be inoperant under 7-8 Volts.

You should be aware K engines last well and 100k miles should not see significant reduction in compression.

A few things in my mind......

Fuel lines at the front of the tank connected right way round?
Plug connector if it is in the front left of the tank is prone to poor connection but you can open the pins a little.
Frame painting means paint at the earth point under the tank may cause electrical isolation so check that earth point.
FICU unit under the seat and the ICU unit at the head stock have big plugs and pins need to be cleaned up from time to time as routine maintenance, higher risk if the are off the bike for a while as you can get surface build up.

Hi y'all,

So I have cleaned all the injectors and they were a little gummed up but all have a nice spray pattern now. 

I have checked compression and that's all good (it's a bit low but still actually better than last summer when it was running okay) Whislt doing this job I cleaned the spark plug connections. (they are brand new spark plugs too)

I have changed the battery and the cranking over seems much muh stronger, so the battery definitely a weal point not helping.

But still not firing up....

I chekced the injectors spraying whilst in-line and it looks nothing like when I was cleaning them, very poor and weak spray not anything like when I cleaned them. The far injector barely had anything coming out.

So my suspicions lie in the fuel pump or fuel filter, and seeing that the tank was off for months empty this would make sense I guess. From what I can hear and see the pump does work, the fuel recirculates back to the tank, there is some pressure in the lines. I also used a multimeter on the pump and it gets enough power I think.

Any suggestions on what to do next? change fuel filter, pump, coolant sensor?

Thanks again everyone.

Jon





BMW K100RS 1985 (UK)

clnl_hrkr wrote:So I have cleaned all the injectors and they were a little gummed up but all have a nice spray pattern now.

I chekced the injectors spraying whilst in-line and it looks nothing like when I was cleaning them, very poor and weak spray not anything like when I cleaned them. The far injector barely had anything coming out.

I don't understand the connection between the events you're describing here. You indicate the injector pattern looked good now then it doesn't look good. How did you check the spray pattern the first time compared to the second time; what happened in between these checks and what was the time interval between them?

In Reply 17, Olaf indicates that the delivery and return lines could possibly have been connected to the wrong ports beneath the tank when the tank was reinstalled. Have you verified that these hoses are connected to the correct ports?

If you don't know when the the fuel filter was last replaced, replace it. Verify that the internal fuel hoses aren't split and that they are tightly connected. After that, checking fuel pressure at the delivery hose to the rail would be a good step.

Fuel pressure regulator?

Mike

Laitch wrote:

clnl_hrkr wrote:So I have cleaned all the injectors and they were a little gummed up but all have a nice spray pattern now.

I chekced the injectors spraying whilst in-line and it looks nothing like when I was cleaning them, very poor and weak spray not anything like when I cleaned them. The far injector barely had anything coming out.

I don't understand the connection between the events you're describing here. You indicate the injector pattern looked good now then it doesn't look good. How did you check the spray pattern the first time compared to the second time; what happened in between these checks and what was the time interval between them?

In Reply 17, Olaf indicates that the delivery and return lines could possibly have been connected to the wrong ports beneath the tank when the tank was reinstalled. Have you verified that these hoses are connected to the correct ports?

If you don't know when the the fuel filter was last replaced, replace it. Verify that the internal fuel hoses aren't split and that they are tightly connected. After that, checking fuel pressure at the delivery hose to the rail would be a good step.

When I cleaned them I did it on my tool bench hooked up to a batery and pumped carb cleaner through them with a tool I made, it cleaned them and I could see a spray pattern which looked uniform and what I'd expect.

Once installed back on the bike and the spray pattern was weak and intermitent. 

The hoses are definitely correct.

Is there a DIY way of checking ythe fuel pressure?

Thanks for your reply, much appreciated

If you are a member of the BMW Club UK, then in their Tool Hire scheme they have a gauge for measuring the fuel pressure (Approx. 4.7 Bar out of the pump and 2.5 bar at the rail). The output is approx. 45 Litres per Hour.

Mike

So I have identified it's the Fuel side that is the issue. I gave the bike a blast of "quick start" and it started right on the button and ran for 10 seconds whilst spraying, it wouldn't keep running though.

I feel that although the fuel pump works it is not pumping enough pressure.

Before I change the fuel pump and fuel filter what other checks could I perform?

Fuel pressure regulator?
Vacuum hoses?
Would the coolant sensor cause this?

I dont want to change these things if it could easily be identified as somthing else like a cracked vacuum hose.

Thanks folks

Take the fuel filter out and try blowing through it.

duck wrote:Take the fuel filter out and try blowing through it.

You absolute legend!!!!!! Turns out the filter hadn't been changed since 1999! I could hardly blow through it, I wanted to see wht was insode so ground the welds off and it was completley gunked up. Thank you so much mate, I can sleep again now.

If you want to see a picture search instagram for bmw.k100.project thats where my updates are.

Thanks again