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Thread: Possible emergency, or am I being a wuss?

  1. #1
    Rally Rat
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    Possible emergency, or am I being a wuss?

    1977 bmw r75/7

    So I rode from San Antonio to Austin. About half way there, the bike developed an odd 'stutter'.

    At random intervals, the engine would skip a few beats. Not a backfire, just... nothin.. maybe 2-3 beats, and then it would pick right back up.

    However, from San Marcos to Austin, the problem has intensified in frequency, but not in severity.

    My worry is that the bike is going to die, halfway home.

    I'd like to get some help figuring this out, and, if possible, fixing it.

    my fuel filters appear to be shiney and clean, and I seem to be getting fuel.

    I have plenty of oil, possibly a little too much oil.

    I dropped the bowls, and they both had some fine, -incredibly- fine, rust powder in the bottom of the bowls. I flushed them, and flushed the float valves, and put everything back together. No change.

    Any help would be greately appretiated, walking home sucks.

  2. #2
    Rally Rat
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    I'd mix a dose of Techron into the tank and change out the fuel filter if possible.

    Check that your spark plug wires are tight.

  3. #3
    Lost again Texpaul's Avatar
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    It sounds like you petcocks could be clogged with...possibly rust? Another possibility is that you may have gotten some bad gas. I.E. it may have water, and who knows what else, in it. Get some HEAT (red bottle) at any auto parts store and dump it into the tank. Give it a few minutes.
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  4. #4
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    stutterrrrrrr

    Quote Originally Posted by Roguetek View Post
    1977 bmw r75/7

    So I rode from San Antonio to Austin. About half way there, the bike developed an odd 'stutter'.

    At random intervals, the engine would skip a few beats. Not a backfire, just... nothin.. maybe 2-3 beats, and then it would pick right back up.

    However, from San Marcos to Austin, the problem has intensified in frequency, but not in severity.

    My worry is that the bike is going to die, halfway home.

    I'd like to get some help figuring this out, and, if possible, fixing it.

    my fuel filters appear to be shiney and clean, and I seem to be getting fuel.

    I have plenty of oil, possibly a little too much oil.

    I dropped the bowls, and they both had some fine, -incredibly- fine, rust powder in the bottom of the bowls. I flushed them, and flushed the float valves, and put everything back together. No change.

    Any help would be greatly appreciated, walking home sucks.
    even if the filters look shiny on the outside they may well be plugged
    try blowing them out or replace them from any auto supply store around the corner
    look in the tank and you may find gunk in the bottom
    You may have the pet cock tubes plugging up,try blowing back through the hoses this may clear them if this is the case

  5. #5
    Administrator 20774's Avatar
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    Float heights OK? Try cracking the gas cap and see if the problem goes away.

    If the problem is stuttering as you say, and the frequency increased, I'm wondering how the gas side could react this fast to give a stutter. I'm wondering if this isn't really electrical. Maybe corrosion in the coil towers, arcing spark plug wires, a loose cross-over wire between the coils.
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  6. #6
    James.A
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    Quote Originally Posted by 20774 View Post
    Float heights OK? Try cracking the gas cap and see if the problem goes away.

    If the problem is stuttering as you say, and the frequency increased, I'm wondering how the gas side could react this fast to give a stutter. I'm wondering if this isn't really electrical. Maybe corrosion in the coil towers, arcing spark plug wires, a loose cross-over wire between the coils.
    Along these lines, the points, condenser and connections associated with these can produce a stumble. It happened to me in Iowa last fall.

  7. #7
    Rally Rat
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    First of all, Thanks! I really appretiate the quick responses.

    The filters are brand new, and have perhaps a hundred miles on them.

    the spark plugs are a touch old, perhaps a replacement might help.

    valves and timing were set about 1000 miles ago, using new points and condenser.

    the coils have never given me a problem -before-... but that's not saying much.

    the plug wires are also new, and about a thousand miles on them as well.

    the onset of this problem was -sudden-. And, does seem to be linked to speed. The faster I go, the more it happens. If I ease off, it eases off

    I can make 70mph without real concern, I just dont want to get stuck halfway home.

  8. #8
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    Quote Originally Posted by Roguetek View Post
    ...And, does seem to be linked to speed. The faster I go, the more it happens. ...
    Sounds like a fuel quality or delivery problem to me.

  9. #9
    James.A
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    Quote Originally Posted by Roguetek View Post
    First of all, Thanks! I really appretiate the quick responses.

    The filters are brand new, and have perhaps a hundred miles on them.

    the spark plugs are a touch old, perhaps a replacement might help.

    valves and timing were set about 1000 miles ago, using new points and condenser.

    the coils have never given me a problem -before-... but that's not saying much.

    the plug wires are also new, and about a thousand miles on them as well.

    the onset of this problem was -sudden-. And, does seem to be linked to speed. The faster I go, the more it happens. If I ease off, it eases off

    I can make 70mph without real concern, I just dont want to get stuck halfway home.

    If it gets to the point of annoying or slowing up the trip then you owe it to yourself to check out a few of the issues raised by our fellow airheads. In my Iowa instance, I was able to get home with only an occasional stumble. I found that the rubbing block where the points ride against the cam had worn enough to knock about .004 of gap out of the equation. This with about 1000 to 1500 miles since the last tune-up.

    The clutch started slipping as well, but that's a whole other story.

    On the fuel delivery side, if you typically ride with one petcock open, try using both. This assumes that the fuel crossover is plumbed in.

  10. #10
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    crossover is plumbed in, and I ride with both valves open.

    Going to start with draining the tank, and cleaning the petcocks vigorously, and doing the same with the filters. Can't hurt, and it doesn't cost anything.

    dammit, why does it always happen when the tank is -full-?

  11. #11
    ABC,AMA(LIFE),MOA,RA,IBMW MANICMECHANIC's Avatar
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    Drop the float bowls and see if there is anything there that doesn't belong, such as water. How soon following a gas stop did this begin?
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  12. #12
    James.A
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    Well then, the tank is easier to lift off when empty. You might as well have a look at the spark plug leads and coil wiring as well.

  13. #13
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    In regards to checking the bowls, other than some incredibly fine rust powder, there didn't seem to be anything that didnt belong.

  14. #14
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    fuel flow

    Usually, fuel flow problems happen at higher speeds first - when the engine needs most fuel flow. Also check the tank to make sure that the air intake is free, allowing fuel to flow, and not creating a vacuum. I've had several engines (Not BMW) where the air inlet (usually through a gas cap) got plugged or gasket got misaligned and this did not allow fuel to flow. I am not sure how this is accomplished on your BMW, but it has to be there somewhere.

    Water in the gas will show itself in the bowls as a "bubble" in the gas at the bottom of the bowl - as water is heavier than gas - and the main jet sucks it up from time to time making an engine stutter.

    I have also seen spark plugs have the same affect - engine stutter from time to time, or a mis-fire - and this on lots of motorcycles - but usually on more racey higher tech engines.

  15. #15
    Airhead or Nothing
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    If the petcocks still have the internal mesh screens on them, these can plug up and stop any sediment/rust/whatever from getting to the external filters.

    Given what you say about the rust, I would guess it is these filters that are clogging up. One thing you can do, that has been suggested, it to blow through the fuel lines back through the petcock filter. If you feel any real resistance, these may be plugged up.
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