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Thread: What grade of gasoline for my 1991 K75 RT ?

  1. #1

    What grade of gasoline for my 1991 K75 RT ?

    Here in western Canada we now have 4 grades of gas starting at 87 octane and up to 93 I think it is. The top 2 contain ethanol the attendant says. I remember reading something about ethanol being bad for EFI . I don't remember much of the article because at the time I had no idea ethanol was being added to our gas . My bike is a 1991 K75 RT .
    On other bikes I remember switching from premium to regular to see if millage or anything changed ,and I didn't notice any difference .
    Any advise will be appreciated .

  2. #2
    Here in Georgia we have 93 octane with up to 10% ethanol. The non-ethanol premium is typically 90 octane. If I'm pretty sure I'm going to running most of the tank out and the K75 bike will not sit for a long period I just use 93. Otherwise 90 non-ethanol. Haven't had any issues. But as they say YMMV.


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  3. #3
    New_AlaBeemer HSVPhil's Avatar
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    What He Said, Mr X:

    If U intend to ride your K75, then I’d say using “high-test” would be preferable for better performance & cleaner mechanicals.
    If U don’t intend to go thru your tanks on some longer rides, get the non-ethanol with the highest octane.

    Here in the Tenn River valley, “some” Murphy’s stations at Wal-Marts now have N.E. 93 Octane with separate Blue hoses, but some don’t... Ya just never know from one location to another (especially across state boundaries). But we tend to burn thru many tanks of petrol doing the CoddiWomple V 2.0.

    Use your best judgement; all will be Okay in the long run...

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  4. #4
    RK Ryder
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    In Canada, Shell V Power claims to have no ethanol. I was told the same about ESSO but found at least one ESSO premium grade recently which stated 10% ethanol. Rubber bits in old K Bikes tend to deteriorate with ethanol fuel. Hence I use, whenever possible, Shell V Power in Canada and attempt to find ethanol free petrol in the US, sometimes successfully, sometimes not.

    I do not know about my ‘87 K100, but my ‘98 R1100RT, definitely gets better mileage with ethanol free fuel.

    I have been meaning to getting around to ordering a kit from Bob’s BMW (but unfortunately I am a procrastinator) which replaces an old K’s tank rubber items with something compatible with ethanol.
    Paul F. Ruffell
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  5. #5
    Dances With Sheep GREGFEELER's Avatar
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    BMW specifies 87 AKI (Octane) Regular fuel. A 10% or less mixture of Ethanol won't matter as long as the AKI rating is 87. Running a higher AKI/Octane rated fuel will *not* make your bike run better, and in fact Premium fuels (91 AKI) are not "better" because they are designed to burn slower than Regular fuels to prevent pre-ignition in very high compression engines and won't deliver as much power in a K75 - at least in theory.

    If you can access non-ethanol Regular fuel then I would suggest you run it all you can for the protection of all the rubber bits in your fuel system: the mount for the fuel pump, in-tank hoses, and the external feed and return fuel injection hoses. Ethanol is very hard on rubber not designed for it, and the K100/K75 fuel systems were not designed with alcohol-resistant rubber parts.
    Greg Feeler
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  6. #6
    #13338 PGlaves's Avatar
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    Quote Originally Posted by GREGFEELER View Post
    If you can access non-ethanol Regular fuel then I would suggest you run it all you can for the protection of all the rubber bits in your fuel system: the mount for the fuel pump, in-tank hoses, and the external feed and return fuel injection hoses. Ethanol is very hard on rubber not designed for it, and the K100/K75 fuel systems were not designed with alcohol-resistant rubber parts.
    However, after market replacement fuel pump mounting dampers which are alcohol fuel resistant may be bought from Euromotoelectrics and Bob's BMW - and probably others.
    Last edited by PGlaves; 08-07-2022 at 02:36 AM.
    Paul Glaves - "Big Bend", Texas U.S.A
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  7. #7
    Quote Originally Posted by GREGFEELER View Post
    BMW specifies 87 AKI (Octane) Regular fuel. A 10% or less mixture of Ethanol won't matter as long as the AKI rating is 87. Running a higher AKI/Octane rated fuel will *not* make your bike run better...
    For some reason I had it stuck in my mind the K75 has a higher compression ratio than it does. You are correct it there is no reason to run higher octane fuel than the specified octane level unless the premium is ethanol free ( Shell V-Power assuming it really is ethanol free) and the regular isn't. Even then it's your choice.


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  8. #8
    Dances With Sheep GREGFEELER's Avatar
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    Quote Originally Posted by PGlaves View Post
    However, after mraket replacement fuel pump mounting dampers which are alcohol fuel resistant may be bought from Euromotoelectrics and Bob's BMW - and probably others.
    Good point, and one I'm going to take advantage of as part of my fall maintenance of my fleet of K-bikes.
    Greg Feeler
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  9. #9
    #13338 PGlaves's Avatar
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    Quote Originally Posted by GREGFEELER View Post
    Good point, and one I'm going to take advantage of as part of my fall maintenance of my fleet of K-bikes.
    I bought five a couple of years ago.
    Paul Glaves - "Big Bend", Texas U.S.A
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  10. #10
    Dances With Sheep GREGFEELER's Avatar
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    Quote Originally Posted by PGlaves View Post
    I bought five a couple of years ago.
    Paul, do you still have five K-bikes? If so, then you're ahead of me.
    Greg Feeler
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  11. #11
    #13338 PGlaves's Avatar
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    Quote Originally Posted by GREGFEELER View Post
    Paul, do you still have five K-bikes? If so, then you're ahead of me.
    Not 5, just three. Two low seat standard bikes and one RT police bike.
    Paul Glaves - "Big Bend", Texas U.S.A
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  12. #12
    Dances With Sheep GREGFEELER's Avatar
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    Quote Originally Posted by PGlaves View Post
    Not 5, just three. Two low seat standard bikes and one RT police bike.
    I have the K75 Standard, the K75S, and the K1. I'm not counting the K12OORS since it's really so different.
    Greg Feeler
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  13. #13
    #13338 PGlaves's Avatar
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    Quote Originally Posted by GREGFEELER View Post
    I have the K75 Standard, the K75S, and the K1. I'm not counting the K12OORS since it's really so different.
    We sold Voni's K75S. I wish we hadn't, but???
    Paul Glaves - "Big Bend", Texas U.S.A
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  14. #14
    3 Red Bricks
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    Paul,

    Did you forget about the S you have stashed at your son’s house in Kansas?





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    Lee Fulton Forum Moderator
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  15. #15
    Dances With Sheep GREGFEELER's Avatar
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    Quote Originally Posted by 98lee View Post
    Paul,

    Did you forget about the S you have stashed at your son’s house in Kansas?





    Greg Feeler
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