Trying to restore a 1989 K100RS that has been standing still for 10 years and have run into some problems on the way.

Thins I've done so far is:

1. Change all the fuel lines
   
2. New fuel pump and fuel filter
   
3. Oil change
   
4. New fuel injectors(The old ones didn't work anymore)
   
5. Cleaned the throttle body
   
6. New spark plugs DPR8EA-9 ( not sure these are correct?)
   

Now the problem is when I start it after it has been standing still for a couple of days it backfires and then gas comes dripping out of the exhaust.
This is where I am stuck at the moment and would like some feedback.

Also, I am unsure of the spark plug wires are correct since I accidentally took them off without marking the order of them. But I have got the bike running with only using starting gas.

If yours is a 16v engine then plug with R in it is correct as it uses resistor plugs. If its a 2v then use plugs without R, they don't use resistor plugs.

I am guessing here but wonder are you getting gas pressure too high due to a faulty fuel pressure regulator. This is in between the throttle bodies and airbox on 2v engines, with a vacuum line from the end of the throttle bodies beside the coils that is routed into it. If that's cracked no vacuum, bad running and fuel pressure way too high. You also have 3 vacuum caps.....again same effect.

But standing a few days and gas coming out is also possibly suggesting an alternative of fuel leaking in.....injectors are normally the only way that happens, as in stuck open. Pull plugs before firing up and check each cylinder....should all be clear at that point.

One could ask what injectors you replaced the original ones with?

A faulty temperature sensor or bad connection can cause over fueling. There is a procedure for testing on this site. Try starting the bike with # 6 Kraffstoppe fuse removed, you will have to manipulate the throttle. It should start but run badly and as the engine starts to die ram the fuse back in. It helps if you have two people one on the throttle and one on the fuse.

Regards Martin.

Thanks, Olaf, my bike is an 8 valve engine so I will go and get new spark plugs.

And I have already gone over and checked for cracks but maybe have to do that again so I can rule that out.

The gas only starts leaking when I am trying to start it otherwise there is no leakage.

I got used fuel injectors from a used K100 that was in working condition.

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I will try that out as well Martin!

D7EA is the correct plug for a 2V K100.

What Martin said about bad or poorly connected temp sensor causing overfueling.

Backfiring and fuel in the exhaust?
 ...I trust you are not twisting the throttle whilst trying to start a fuel injected bike....don't touch the  throttle at all!, just hit the start button (with the fast idle/choke set on the first notch)

Getting at the temp sensor will also tick off a few other jobs like cleaning and flushing the rad/cooling system, checking the fan, cleaning filler cap, cleaning out a few other electrical connections under the tank.......


I could have said you just need to take off the rad.....

Thanks for the help, will get back as soon as I have tried everything you have said.

A local aftermarket BMW tech had a K75 in his shop recently that would piss fuel when cranking. He looked at 'everything' and was quite frustrated. Turned out to be a loose connector plug up to the AFM unit and a slightly sticking flap. Runs a charm after a bit of fiddling.

MartinW wrote:A faulty temperature sensor or bad connection can cause over fueling. There is a procedure for testing on this site. Try starting the bike with # 6 Kraffstoppe fuse removed, you will have to manipulate the throttle. It should start but run badly and as the engine starts to die ram the fuse back in. It helps if you have two people one on the throttle and one on the fuse.

Regards Martin.

I think i have found the problem now. I removed the fuse as you sugggested and gave it a lite throttle then it started after a couple of tries but died directly after a few seconds. Also as soon as the fuse was back in it started to drip gas again but once removed it stopped. So im guessing the problem lies there somewhere. What would the next step be?

Clean the temperature sensor connector, mine played up twice until I cleaned it properly with DeoxIT. Due to it's location it is a pain to get to and is subjected to road spray. I also smeared dielectric grease around the connector to stop water ingress and exclude air that leads to corrosion. If that doesn't work you need to test the sensor.
Regards Martin.

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It's not THAT hard to get to the temp sensor.  You just need to get the air box out of that way.

http://www.kbikeparts.com/classickbikes.com/ckb.tech/0.ckb.tech.files/maf/maf.htm

Felow wrote:This is where I am stuck at the moment and would like some feedback.

I am unsure of the spark plug wires are correct since I accidentally took them off without marking the order of them.

Once you have installed the correct plugs with correct gaps and connected them correctly according to duck's diagram in post #7, one relatively simple task is to disconnect the fuel pressure regulator's vacuum hose to check it for the presence of fuel. That would indicate a diaphragm leak which could cause a rich running condition, as Olaf indicated in post #2.

Carefully pull it from its connection at the throttle body indicated by the red arrow on the photo.

If you have OEM plug wires with the metal caps, you can read the cylinder numbers printed on the wire.  #1 is the front.

If in doubt, the coil nearest the front is for cylinder 1 and 4, both these leads spark at same time every stroke, doesn't matter if you mix up 1 and 4 as its got what is called wasted spark. If my memory is correct no 4 is actually a long lead that loops around not 2 plug and then comes back to no 4.

The coil nearest rear wheel is for 2 and 3 and same applies. Doesn't matter if you mix up 2 and 3.