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Discussion Starter #1
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 :|
 

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Discussion Starter #5
Check the Earths and block connector first.
I just cleaned every electrical connection about 2 weeks ago.

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 :|
In-tank hoses are a good thought. I replaced the fuel filter last summer and they looked fine at that point so I had ruled that out but that was probably a dumbass thing to do when fuel pressure seems like the issue.
The test method isn't great, I'll give you that.

check the fuel pressure, don't just replace shit for no reason.
Everything I mentioned replacing I did for other reasons. I do need to borrow a pressure gauge and check it though. Didn't get the chance over the weekend.
 

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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
 

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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?
 

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I know you guys probably covered this, but... When you are dealing with in-tank fuel hose, make sure you get the most modern ones rated for submersion. I think you want hose rated 30R10. If it doesn't have to be in the tank, 30R9 is good enough. I am pretty sure the older hoses, even 30R7 doesn't handle the alcohol in today's fuel, or old fuel (sitting for the winter) nearly as well.
 

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Discussion Starter #10
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.
 

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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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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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. 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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