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BMW K100 runs rough, cuts out, won't start back up

5166 Views 12 Replies 7 Participants Last post by  crazypj
Greetings gents,

Been having an odd problem with my K100. It'll start briefly if it's cold. After running rough at idle and stalling, I took the spark plugs out and all 4 were wet and had carbon buildup so I'm guessing the reason it won't start back up is flooded cylinders. If I unplug the injectors and start the bike, it'll run for about 5 seconds and die again from lack of fuel. After that, I unplugged the fuel pump and started the bike up. It runs a bit, then starts to die. If I plug the fuel pump back in really quickly then pull the plug again, the engine will dip in revs for a second or two, then come back up. If I keep repeating this cycle, the bike runs. The only way to keep the bike running with the fuel pump plugged in is to bring it up to about 5k rpm, which takes some doing.

It's like it's getting way too much fuel. I replaced the injectors and nothing changed. I just replaced the rubber intake parts, so there shouldn't be a vacuum leak. I recently replaced the hall effect sensor, so I was thinking I may have gotten the timing wrong, but it seems like it would be difficult to get it so wrong that the cylinders flood. So the next thing I'm going to try is replacing the fuel pressure regulator. I'm thinking maybe it's not working correctly.

Is there anything else I should be checking? I've been banging my head against the wall with it for a while now.
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Sure sounds like your fuel pressure is a problem; check your filter as well as all of the little rubber hoses inside the fuel tank, when it is running look inside the fuel tank and see if there is fuel movement where there should not be.

I had a small black rubber hose rot off inside the fuel tank and it did something very similar, had a crack in a fuel filter canister once too and it ran but like crap that time too.
btw: The test method you are using sure doesn't sound like anything I have ever read in a service manual :|
Everything you could want to know and more about K100 Fi
Bit of a frustrating weekend, as it turns out. Checked the fuel pressure and it was right where it was supposed to be at 36 psi. Changed out the spark plugs and got the thing fired up to let it run for a bit. After a couple minutes idling at around 1500 rpm, steam started coming from the radiator. I drained the coolant and there was oil in it. Looks like I've got a blown head gasket. I've managed to kill the world's most reliable bike.
Or you found out what was wrong with it to begin with.
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