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

5165 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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What year is your K100? I know they are older bikes, but was BMW using any sort of computer fuel management in the later years? I ask this because I had a 87' Ford Ranger once (I know bikes and cars are not entirely similar) and it had this weird "in-between technology" carburetor/computer" set up. While it was carbed, the ECU still controlled the fuel delivery to a point. When I had to rebuild the top end I could never get the thing to idle properly because of that damn ECU. I fought with it for weeks before I finally gave up and sold it for cheap, not knowing that a $100 replacement ECU would have fixed my problem.

Point is, does your K100 have something like that? Some odd piece of German tech that you wouldn't otherwise think twice about?
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.
Eh, shit happens. Something like 1 in every 1000 TV's that roll off the line are shitboxes, all 999 other TV's may last forever, but not the one. Might not have been your fault, hell likely it was just a bad gasket and was bound to happen eventually.

It's like when I borrowed a friends air compressor. He bought it brand new a year prior, used it all the time with no issues for hours at a time. I get it and run it for 15 minutes and the damn thing blows some internal valve and is ruined. Was going to happen, just happend to be when I was using it.
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