BMW K bikes (Bricks)

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1Back to top Go down    Sputtering on Sat May 19, 2018 9:41 pm

timz10000

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My 85 K100 has taken to sputtering and cutting out but not dying - usually in a 30 minute ride this will happen a few times. In the last year I've cleaned the starter, kill switch, & light switch, and it has a new Hall sensor so I know it's not those.

Here are the symptoms, seems like upon acceleration around 3-4k on the odo it starts sputtering and losing power. If I pull in the clutch and gun it I can get it revving again after a few tries. Even when it's sputtering and cutting out, it will idle. I notice sometimes when I just start the bike, the battery light comes on, and goes off when I rev it a little.

Could this be either a bad battery or the alternator?


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1985 K100
    

2Back to top Go down    Re: Sputtering on Sun May 20, 2018 12:04 am

MartinW

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Check the fuel rail pressure (36 PSI), when was the last time you changed the fuel filter? Check in the tank that all the fuel lines are tight.
Regards Martin.


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3Back to top Go down    Re: Sputtering on Sun May 20, 2018 12:41 am

timz10000

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@MartinW wrote:Check the fuel rail pressure (36 PSI), when was the last time you changed the fuel filter? Check in the tank that all the fuel lines are tight.
Regards Martin.
To check fuel pressure should I take the rail off and see if the injectors are squirting, or do I need a pressure gauge of some kind?

I'll check the fuel filter -maybe the filter has gunk in it - the tank had a little old lining floating around that i fished out at one time.

I checked that the lines are tight (but they're replacements I put in of the hard plastic type like this http://www.euromotoelectrics.com/product-p/fp-hosekit.htm and I was wondering if they got kinked but didn't see that in there).

It also behaves like it's running out of gas when the gas is at the bottom section of the tank but there's still a gallon or so in there - I wonder if maybe one of the metal tubes has a crack or something. I wonder if that ever happens.


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1985 K100
    

4Back to top Go down    Re: Sputtering on Sun May 20, 2018 12:59 am

nobbylon

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Mine does this when the 4 litre light comes on and I accelerate or throw it around a little. Try and see if it does it with a fuller fuel tank.


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R1100GS Feb 1995
K100RS July 1989
K100 Dec 1983
R90s June 1975
R75/6 Feb 1976
F650GD May 2001
    

5Back to top Go down    Re: Sputtering on Sun May 20, 2018 3:29 am

MartinW

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The gauge needs to be put into the return line back to the FPR. My gauge was sourced from an old compressor regulator. From your last post it sounds like you might want to pull the fuel pump and check it and the screen for debris. You might want to also flush out the tank and remove any remaining debris. Running the tank down that low virtually assures you that you are going to pick up any crap that is floating around, and as nobbylon said it can cause cutting out as the fuel surges away from the pickup screen. The fuel pump also relies partially on cooling from the surrounding fuel and in a Qld summer I have had vaporization problems from running with 5-7 litres left.
Regards Martin

R


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6Back to top Go down    Re: Sputtering on Sun May 20, 2018 2:32 pm

timz10000

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@MartinW wrote:The gauge needs to be put into the return line back to the FPR. My gauge was sourced from an old compressor regulator. From your last post it sounds like you might want to pull the fuel pump and check it and the screen for debris. You might want to also flush out the tank and remove any remaining debris. Running the tank down that low virtually assures you that you are going to pick up any crap that is floating around, and as nobbylon said it can cause cutting out as the fuel surges away from the pickup screen. The fuel pump also relies partially on cooling from the surrounding fuel and in a Qld summer I have had vaporization problems from running with 5-7 litres left.
Regards Martin

R


Thanks. One more question - if I take the fuel filter off can I see if it has gunk in it? Can it be flushed in reverse? Or do I just have to replace it if I suspect it isn't clean? I can't remember.


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1985 K100
    

7Back to top Go down    Re: Sputtering on Sun May 20, 2018 2:42 pm

Inge K.

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@timz10000 wrote:
if I take the fuel filter off can I see if it has gunk in it?

No problem.......you need a can opener, and a new filter.

The filter is one time use, as you have a history with gunk floating around...
flush the tank and get a new filter.


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Inge K.
K100RS -86. (first owner), K1100LTSE -94.
    

8Back to top Go down    Re: Sputtering on Mon May 21, 2018 5:31 pm

glennpm

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Regarding, "To check fuel pressure should I take the rail off and see if the injectors are squirting, or do I need a pressure gauge of some kind?"

You need a gauge. I had starting trouble a couple of months back and although the fuel pump was pushing fuel, the pressure was about 20% of what it should be.

Glenn

    

timz10000

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Wow - so I replaced the fuel filter and when I was checking the fuel pump (the screen on the bottom looks good, I replaced that and the rubber boot a year ago) lo and behold I found there was this big ugly piece of ... bondo? right underneath the intake screen. I'm guessing this was blocking the fuel flow.

I removed it, reseated the pump. The bike now doesn't cut out, but it doesn't feel quite right - not quite as much power as before. I'm going to give it a longer test ride tomorrow. I synced the air intakes last year with a manometer, one thing I'm wondering is if I synced those based on the blocked fuel flow. Not sure. (I also know my exhaust valves are a little tight, not sure if that relates to this at all).

Another culprit could be the alternator? The battery light started to glow a couple times when it was running not great, but I tested the battery at an Autozone and they said it looks good, full charge.


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1985 K100
    

10Back to top Go down    Re: Sputtering on Tue May 22, 2018 1:08 am

MartinW

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It is sometimes possible if the filter is pretty blocked for particles to get pushed through the filter and partially block an injector. Did you clean out the tank, if not you will probably end up with the filter blocking again.
Regards Martin.


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11Back to top Go down    Re: Sputtering on Thu Jun 07, 2018 11:46 am

timz10000

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Thanks everybody! I cleaned out the gas tank really well and now it's running great.

(The tank had a layer of tank sealer that I tried soaking with Goo Gone, scrubbing, and then finally realized the way to remove it was spending a couple hours slowly peeling it off everywhere like you peel skin off a sunburn)


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