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Thread: 71 r75/5 New owner stumped on throttle not returning

  1. #1

    71 r75/5 New owner stumped on throttle not returning

    I purchased a 71 r75/5 about 6 months ago and have been working and riding it on and off during that time. Recently bought a mikunis carb conversion and I am having an issue with the throttle returning to closed. Enough time has lapsed that I can't remember if I always had to force the throttle closed. I order a new throttle cam gear and throttle tube and it still does not want to return on it's own power. I should mention that for some reason the new throttle tube does not fit so I am still using the old one. Think they may have sent an incorrect part. The cables are new and don't seem to bind. When I pull the cable end it seems to move back with sufficient power. I have a 2 cable system. Any pointers on setting this up send what to check would be great.

  2. #2
    Liaison 20774's Avatar
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    Welcome to the forum! First check the easy stuff. Are you aware of the screw that's on the underside of the throttle housing? Number 16 in this figure:

    https://www.realoem.com/bmw/enUS/sho...diagId=32_0752

    That's primarily used to lock the throttle during routine maintenance...it can hold the throttle at a constant setting. Secondarily, it has been used while riding to create a bit of friction on the throttle to slow it's tendency to close...kind of a crude cruise control.

    Let us know what you find.
    Kurt -- Forum Liaison ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  3. #3
    Right now that screw is removed

  4. #4
    Liaison 20774's Avatar
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    OK, great! So you say that the cables, when pulled by themselves, seem to have some return tension to them. With the cables unhooked from the throttle tube, when you turn the throttle tube does it have resistance? I suspect that there might be a minor amount of resistance to turning, but if it takes quite a bit of effort, then there is some binding or it needs lubrication, or it's not the right part.
    Kurt -- Forum Liaison ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  5. #5
    The original tube had some webbing missing and the teeth were looking fairly sharp and worn. The new tube does not want to slide in all the way. Cleaned out everything and cannot see where the new part is not fitting correctly. 32721233307 is the replacement throttle tube I got. Is this not the correct part. Also thanks for your help.

  6. #6
    Liaison 20774's Avatar
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    That part number seems to be correct per RealOEM:

    https://www.realoem.com/bmw/enUS/sho...52#32721233307

    Sounds like you need a second pair of eyes to look things over...sure seems like there's some interference.

    Where are you located...would be helpful if that was in your profile? Potentially someone near you could come by. There is the Anonymous Book...have you looked to see if there's an Airhead owner near you? The Airheads Beemer Club has tech days scheduled in various states throughout the year...maybe there's something coming up.
    Kurt -- Forum Liaison ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  7. #7
    '99 '03 '06 National Co-Rally Chair Friedle's Avatar
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    Another easy check for sticking throttle cables. Is the rubber hand grip rubbing against the front brake perch impeding free rotation? The friction between the hand grip and the perch can make throttle return slower.

    Friedle

    Airheads Beemer Club www.airheads.org
    Ride fast safely

  8. #8
    Registered User 6322's Avatar
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    If the throttle/brake perch is pushed too far onto the handle bar, the inside of the grip may be dragging on the end of the bar.
    Gary Phillips - #6322
    Wildland Firefighter, Retired, Riggins, ID
    Heartland Moto Locos BMW Riders
    '77 R100/7 Dirt Hack, '83 R80ST, '85 K100RS w/EML, '00 R1100RS

  9. #9
    Thanks for the suggestions, will take another look tomorrow. I feel like itís something really obvious That I just keep missing. Also i am located in Charlotte North Carolina.

  10. #10
    I thought some Mikuni carbs used a double cable setup to pull the throttle open and pull the throttle closed.
    Paul Glaves - "Big Bend", Texas U.S.A
    "The greatest challenge to any thinker is stating the problem in a way that will allow a solution." - Bertrand Russell
    http://web.bigbend.net/~glaves/

  11. #11
    Registered User barryg's Avatar
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    Quote Originally Posted by PGlaves View Post
    I thought some Mikuni carbs used a double cable setup to pull the throttle open and pull the throttle closed.
    Push/Pull throttle

  12. #12
    Well the throttle tube grip was hitting the end of the handle bars. Feel a little stupid for not figuring that out earlier. Thanks for the help.

  13. #13
    Registered User 6322's Avatar
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    Nothing to feel stupid about. If it hadn't happened to me, I wouldn't have known to suggest checking it. Must be time for a ride. Have a good summer. gp
    Gary Phillips - #6322
    Wildland Firefighter, Retired, Riggins, ID
    Heartland Moto Locos BMW Riders
    '77 R100/7 Dirt Hack, '83 R80ST, '85 K100RS w/EML, '00 R1100RS

  14. #14
    Registered User ebeeby's Avatar
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    Quote Originally Posted by gwrodzhi View Post
    Well the throttle tube grip was hitting the end of the handle bars. Feel a little stupid for not figuring that out earlier. Thanks for the help.
    Nah. Now you can help the next guy. Now my pal filling his Porsche Boxster with diesel, that was stupid.
    1973 R75/5

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