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Thread: Airhead slow to return to idle

  1. #1
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    Airhead slow to return to idle

    I have a 1977 R60/7 that I hope someone can help me with.

    The bike has electronic ignition.

    I was having a problem with it idling. It would stall out when you came to a stop.

    It needed a lot choke to start.

    Compression was tested and the compression is at factory specs for both cylinders.

    I replaced the spark plugs and the carbs were cleaned and balanced

    The valves adjusted to factory specs.

    Play was checked in the choke lines and the accelerator lines.

    The previous owner had set the carburetor needle to the second notch and I restored it to the first notch which is the factory specs.

    The idle was set around 1200 rpm which seemed to be a fine. It idled very nicely after all the adjustments were made.

    I normally fuel with standard premium gas at 91 octane ( Shell ), but occasionally I find a station with 93 and will take the higher octane if available.

    It starts easily now, but I notice now that it does not always return to idle quickly when you come to a stop.

    If you are on the highway and running around 5000 rpm, when you come to a stop, the idle may only drop to around 3000 rpm.

    It seems to be an intermittent problem.

    After a while, it may drop down to the 1200 rpm idle speed and the net time I stop, the idle may drop quickly to 2000 or to 1200. It seems unpredictable.

    It is almost as if something is sticking in the carburetor.

    Any suggestions as to what the problem and fix might be would be appreciated.

  2. #2
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    check the rubber diaphragm at the top of the carb? pinpoint hole, or small tear just beginning could be the culprit.
    Ride Safe, Ride Lots

  3. #3
    Administrator 20774's Avatar
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    Welcome to the forum!

    What brand of electronic ignition is installed? Some, particularly the Dyna III, uses the stock advance unit. It can cause the symptoms you're seeing if it sticks "open". Normally, the issue wouldn't be intermittent, but high idle can be cause by a sticking advance unit.

    When the carb changes were made, was it done after the engine was warmed up or was it done cold? Have you checked for air leaks around the carburetor? Try spraying something like carb cleaner around the carb and connection to the intake port of the head...if the RPM changes as a result of that, you have an air leak.
    Kurt -- Forum Administrator ---> 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!

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    The pin hole in the diaphragm wouldn't apply to the R60/7 as they didn't use CV carbs. Related to the last post the problem may be related to the springs on the fore mentioned advance mechanism. A relatively inexpensive fix if that is the case. Also agree with making sure it's warmed up before setting the idle. Ride easy.
    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

  5. #5

    Check the throttle cable routing

    Check the throttle cables for proper length and routing. Sometimes people change handle bars or cables and don't think about the routing or proper cable length, BMW Airheads and Vintage bikes are very sensitive to changes in the cable length & routing.

    Before you go to far into checking or changing things try this

    Bike warmed up, put it on the center stand and start it up, let the idle fall to its lowest point then turn the handle bars slowly from stop to stop several times. If there is no change in the idle do the same test off the center stand and with you sitting on the bike.

    ***Be Very CAREFUL with the amount of time you have the bike running at idle and stationary. The tests I described above shouldn't take more than a minute or two of stationary running time. If you think it will be longer make sure you get a good high volume fan and run it in front of the bike to blow air over the cylinders as if you were riding down the road***

  6. #6
    #4869 DennisDarrow's Avatar
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    Good stuff from Gary, Zeff, and Kurt...........Warm it up, clean up and lube the advance unit, perhaps replace the advance unit springs, and follow instructions about the bars and carbs..........RIDE......God bless....Dennis

  7. #7
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    The mechanical ignition advance mechanism is the first thing one thinks of when a motor wants to idle at a high rate of speed. The extra consideration for 600 cc motors is the mechanical slide-throttle carburetors. It is important that the action of the throttle mechanism is silky smooth from the right hand grip all the way down to the slides in the carburetor.
    1973 R75/5

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  8. #8
    Registered User dmftoy1's Avatar
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    Airhead slow to return to idle

    Quote Originally Posted by James.A View Post
    The mechanical ignition advance mechanism is the first thing one thinks of when a motor wants to idle at a high rate of speed. The extra consideration for 600 cc motors is the mechanical slide-throttle carburetors. It is important that the action of the throttle mechanism is silky smooth from the right hand grip all the way down to the slides in the carburetor.

    Fwiw - a good trick to check for sticking ATU (assuming your electronic ign still uses it) is to get bike warmed up, disconnect neg. Battery cable, and remove front cover. If you hook up a timing light and point at the ATU you can see if the weights are retracted or extended. Don't know why a timing light works better than a good flashlight, but for some reason the strobe effect makes it easier for my eyes to see.

    Good luck!


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  9. #9
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    Quote Originally Posted by dmftoy1 View Post
    Fwiw - a good trick to check for sticking ATU (assuming your electronic ign still uses it) is to get bike warmed up, disconnect neg. Battery cable, and remove front cover. If you hook up a timing light and point at the ATU you can see if the weights are retracted or extended. Don't know why a timing light works better than a good flashlight, but for some reason the strobe effect makes it easier for my eyes to see.
    Not really sure the bike needs to be warmed up for this test...at least to see if the advance weights swing in/out. Before starting, remove the negative battery cable, remove the front cover, then reattach the battery cable. Connect an inductive lead to one of the spark plug wires. Start engine. Then shine the timing light at the advance unit while reving the engine. The timing light flashes at the rate of the spark plug firings which momentarily freezes the rotating parts. A regular flashlight won't really do that.
    Kurt -- Forum Administrator ---> 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!

  10. #10
    Bluenoser
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    If nothing else seems to help, hanging idle ( engine that is slow to return to normal idle ) can be caused by a lean condition. I'd still put my money on the cables, linkage, needle & slide or the choke sticking on. Not sure what carb is on the 60/7 but if they've been apart anything is possible.

    There likely was a reason why the previous owner had the needle in the second position. Easy to change put it back in second position and see what happens.
    1999 R1100s
    1999 GL1500

  11. #11
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    Quote Originally Posted by 20774 View Post
    Not really sure the bike needs to be warmed up for this test...at least to see if the advance weights swing in/out. Before starting, remove the negative battery cable, remove the front cover, then reattach the battery cable. Connect an inductive lead to one of the spark plug wires. Start engine. Then shine the timing light at the advance unit while reving the engine. The timing light flashes at the rate of the spark plug firings which momentarily freezes the rotating parts. A regular flashlight won't really do that.
    kurt,

    advance apologies if I am butchering this. new r100gs owner and new wrench.

    however is one way to check Sticking ATU (per Fleischer) to shut off bike when it is idling high. restart bike and if it is idling correctly then you have a sticking ATU?

    jon

  12. #12
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    Quote Originally Posted by hotwheels22 View Post
    however is one way to check Sticking ATU (per Fleischer) to shut off bike when it is idling high. restart bike and if it is idling correctly then you have a sticking ATU?
    Jon -

    Sounds right...basically, you're seeing if the springs can pull the advance weights back when the engine is at rest. Provided when you restart, you don't necessarily gun the engine, but let it start and come to an idle by itself.

    Another way...maybe try this first. With engine running high, grab front brake (or move the bike against an immovable object), put the bike into gear and slowly let the clutch lever out. You're providing some drag on the engine and if you can slow the engine back down to idle and it stays there after pulling the clutch lever back in, then you've also demonstrated that the advance weights will come back to rest and thus might have been sticking.
    Kurt -- Forum Administrator ---> 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!

  13. #13
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    Quote Originally Posted by 20774 View Post
    Jon -

    Sounds right...basically, you're seeing if the springs can pull the advance weights back when the engine is at rest. Provided when you restart, you don't necessarily gun the engine, but let it start and come to an idle by itself.

    Another way...maybe try this first. With engine running high, grab front brake (or move the bike against an immovable object), put the bike into gear and slowly let the clutch lever out. You're providing some drag on the engine and if you can slow the engine back down to idle and it stays there after pulling the clutch lever back in, then you've also demonstrated that the advance weights will come back to rest and thus might have been sticking.
    hi kurt

    thanks, hopefully the OP will have solved the issue. can I just verify if the solution if it is a sticking set of weights is to literally just open the can and squirt some WD 40 in there? if so is this a good idea for preventive maintenance? and then other than that at some point folks put in a new set of springs?

    THANKS

    jon

  14. #14
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    WD-40 is not to be used in this situation. "WD" stands for water dispersant and once the base liquid in it evaporates, it leaves a gritty covering which only serves to trap dirt. You should use some kind of oil, a light oil. It probably will only help for a little while...a full teardown would be necessary eventually.
    Kurt -- Forum Administrator ---> 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!

  15. #15
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    Quote Originally Posted by 20774 View Post
    WD-40 is not to be used in this situation. "WD" stands for water dispersant and once the base liquid in it evaporates, it leaves a gritty covering which only serves to trap dirt. You should use some kind of oil, a light oil. It probably will only help for a little while...a full teardown would be necessary eventually.
    got it. thanks.

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