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

5252 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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There was an issue with the early K100's where fuel pump would over pressurise system. Worst case, the tank would 'inflate' I changed a few under warranty but never had anything like your describing. You need to check fuel pressure before wasting any more money replacing random parts. Also, check voltages to injectors and fuel pump, I've seen faulty regulators put 17V into them (they don't like it) Often, it's just regulator ground or sensing wire, I've fitted 30 amp relays to get battery voltage direct to regulator which can cure over-voltage issues
. I've managed to kill the world's most reliable bike.
It was probably a previous owner that caused the problem? At least it's a real easy fix as you don't need to pull motor or anything as it's all easy to get at. You may find other problems when you get it apart but I think it's worth doing as you'll have an ultra reliable bike that should outlast you
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