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Thread: Setting throttle stop screws

  1. #1
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    Setting throttle stop screws

    After having a constantly climbing idle, I decided to pull the right hand throttle body off and replace the rubber bits. It seems that at some point along the line, the throttle stop screw was backed off to the point where the butterfly valve no longer comes to rest on the stop screw. So what's the procedure for setting the stop screw? All the balance guides suggest to not touch this particular adjustment, which to me is a fine idea but not an option at this point. What should I do?

    Oh yeah, '95 R1100GS.

  2. #2
    Nickname: Droid
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    Are you sure the stop screws were turned? Is the paint seal still intact and not broken? If so, don't touch those screws. It could be the free play in the throttle cable got messed up to the point the TB plate can't close due to cable tension. If that is the case then someone messed up the TB balance and tried to reset it, improperly. So first off, make sure the throttle cables are not holding the TB plates open. The throttle must have about 10 degrees of free play before either TB plate moves.

    But IF you, or someone, messed with the "sealed" screws no one is ever supposed to touch, and the paint seals are borken, naughty, naughty!

    You will need to use some type of airflow balance device, because those screws are factory set to perfectly match the airflow through each throttle body with a specific amount of air flowing through them on an airflow bench. We don't have that luxury or level of control, so a pair of mercury sticks (manometer), or the electronic style of vacuum sensing meter (Twinmax)is needed. The bike needs to be warmed up, and you'll need a good sized box fan or two to move cooling air across the running engine as you do this, because the first time takes some time.

    1. Make sure the throttle cable has slack and that both TBs are at the rest postition against the stop screws. That also means the cable to the RH TB must have some slack. 2. Bike running, fans blowing, then attach the meter tubes to the vacuum ports on the bottom of the TBs. 3. Assuming the screws have been turned and the paint seals broken, adjust the idle/balance so the engine idles at about 900 rpm (this may take repeated attempts). Don't dawdle at this and let the engine get too hot. 4. If you can get good balance at 900 rpm, the screws are done. 5. Then adjust the Big Brass screws until the balance is further refined and the idle has come up to about 1050 to 1100 rpm. Idle set speed/balance is done. 6. Then adjust the off idle balance at about 2500 rpm by adjusting only the RH TB cable to match the setting to the LH TB.

    If the idle sets up, but one BBS (Big Brss Screw) is turned out significantly more than the other, then the BBS ports are dirty and need cleaning. Turn the screw in until it gently stops, count the turns going in to the stop. Then turn the screw out, remove it, shoot some carb cleaner into the port, and spray the screw and clean the tip. Then reinstall the screws to the setting you counted before removing them. You could also just do this before starting the whole procedure. If the screws/ports are dirty it will be difficult to get them to alter the fine tuning of the balance without gross mismatch side to side.

    That is the basic, rough way to do it and I'm sure others (Paul Glaves) will step in and refine it. If you don't feel comfortable with this, or don't have a manometer or Twinmax, then get the bike to an understanding mechanic with the right tools, skills and knowledge. Oh, and tell him/her what has been done or what you have done to the bike. Never take a bike to mechanic and say "I didn't do anything to it" and expect them to figure it out. If you messed it up, tell him/her, it'll cost you less in the long run and it'll get done sooner.

  3. #3
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    The throttle stops were definitely messed with, at least on the right side. I had the throttle body off the bike and the butterfly was closing by contacting the inside of the throttle body instead of the stop screw, and not due to wear.

  4. #4
    Benchwrenching PGlaves's Avatar
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    In this case you have no choice but to match the two throttle bodies as closely as possible. To do this I would set both brass air bleed screws to precisely one turn open from lightly seated after removing them, cleaning them, and blowing carb cleaner and compressed air into the recess where you removed the brass screws. Then make sure you have free play in the cables, including the high idle (choke) cable.

    Then using a manometer (carb sticks, Twin Max, etc), without disturbing the left throttle body carefully balance the right throttle body to the left throttle body as closely as you can by adjusting the idle stop screw on the right throttle body.

    Change rpm up and down a few times with the twistgrip to be sure that it settles back at idle, in balance.

    Then you can set the idle speed to 1050 or 1100, balanced again, with the brass bleed screws.

    If it will idle slowly with the brass screws precisely 1/2 or even 1/4 turn out from lightly seated that would be even better than the one turn out suggested.

    Once you get them balanced at idle, then proceed to balance them on the cables, just off idle, somewhere around 1200 to 1300 rpm.

    Good luck.
    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://www.bigbend.net/users/glaves

  5. #5
    Curmudgeon nrpetersen's Avatar
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    I'll ask here too. What do the BBS screws do that the throttle body screws don't do? I see both as admitting air (and no fuel) into the engine intakes. Is it somehow different air?

    I could not get my 2000 R1100RT surge & idle cleaned up until:

    1) The valve lash carefully set.
    2) The throttle body & BBS thoroughly cleaned up w a Q-tip and carb cleaner.
    3) The throttle body stop screws adjusted for equal manifold pressure while running with both BBS screws first set out 1 1/2 turns. (Edit - set the TPS wiper to 370 millivolts)
    4) I then adjusted the RH cable for equal manifold pressure at ~3000 rpm.

    I did initially end 2) with the throttle screws set so that there was the slightest and equal sliver of light visible thru the throttle bodies.
    Last edited by nrpetersen; 09-15-2010 at 09:56 PM.
    Retired w 2005 K1200LT, 2000 R1100RT, & 1975 R90/6

  6. #6
    Benchwrenching PGlaves's Avatar
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    The bleed screws allow bypass air to be drawn in by vacuum when the throttle plates are closed or nearly closed. They have very little impact off idle once the throttle body throat is less restricted by the closed throttle plate.

    The idle stop screws set the throttle plate angle at idle and define the size and shape of the crescent shaped air passage when the throttle plate is closed.

    You want to get the angle of the two throttle plates as equal as possible because if your base angle is identical on both throttle bodies then the size and shape of the throats stay the same as the cables pull equally on both sides.

    On the other hand, if at idle one angle is greater, compensated for by less air past the bleed screw, as the bypass air drops out of the equation when vacuum drops, then that throttle body will draw more air throughout the entire range of movement given equal cable pulls. You will not be able to get synchronization across the whole range of openings.
    Last edited by PGlaves; 09-15-2010 at 08:47 PM.
    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://www.bigbend.net/users/glaves

  7. #7
    Day Dreaming ... happy wanderer's Avatar
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    There seems to be a lot of fear out there about the blue thread lock on those throttle body screws. IMO this is thanks to dealer warranty issues that have become almost mythical. I don't understand why one would even worry about this with a bike well out of warranty anyway.

    I think Paul Glaves' instructions will work just fine if no one has moved the left throttle body idle adjust screw and if the throttle bodies are in perfect working order. Mine were not and maybe yours aren't either.

    If you follow Rob Lentini's method of setting them up using his zero-zero procedure you can achieve excellent results. My 96 RT would not idle properly when warm and no amount of big brass screw adjustment would bring it down to 1100RPM. It idled way too fast and surged like it was posessed. I plunged in, cracked the loctite and set them up from scratch using the zero-zero procedure and it worked perfectly so fear not.

    It's pretty straightforward and relies on the TPS (throttle position sensor) voltage and your manometer for accuracy. You do not need a bench flow meter at all.

    The basic steps are:

    1. Loosen throttle cable (left side)
    2. Loosen throttle body crossover synch cable (right side)
    3. Back out the left throttle plate stop screw (underneath left side)
    4. Attach DVM to red-white TPS wire #1 (rear) - ignition on
    5. Move TPS to obtain zero reading (.006 volts) and lock TPS
    6. Move left throttle plate stop screw to obtain .370 volts and lock screw
    7. Large brass bypass screws in, bike on, warm engine, rough idle expected
    8. Turn the large brass bypass screws out in 1/4 increments if bike will not idle; attach
    carb stix (or Twin Max or CarbTune or whatever you choose)
    9. Set right throttle plate stop screw using carb stix
    10 Reduce TPS in increments of 0.020 if idle exceeds 1100-1200 rpm
    11. Reset throttle cable (left side) to .5 mm free play
    12. Perform the Throttle Body Synch.

    Details can be found in this excellent manual. http://www.ibmwr.org/r-tech/oilheads...ce_2-25-02.pdf
    MJM - BeeCeeBeemers Motorcycle Club Vancouver B.C.
    '81 R80G/S, '82 R100RS, '00 R1100RT

  8. #8
    Curmudgeon nrpetersen's Avatar
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    I should have added in my above list to set the TPS wiper to 370 milli-volts after setting the throttle stop screws, which is after arbitrarily setting the BBS to 1 1/2 turns out. In this method the engine intake manifold delta P is used as the matching flow measurement device.

    The initial visual setting of the stop screws was only to get a reasonably good starting point for final settings.

    In my case also the BBS settings were substantially different. Maybe it is the same factory guy that sets FD preloads.

    I still don't see anything sacred about not tinkering with the throttle stops if the BBS screws are messed up, providing everything is clean.
    Retired w 2005 K1200LT, 2000 R1100RT, & 1975 R90/6

  9. #9
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    I stressed not messing with the screws in case you need to take your bike to a dealer for TB balancing. If a dealer mechanic sees the screws have been messed with he may very likely not even want to work on the bike. That was the case when I had brought my RS into the local dealer. The service manager adjusted it, and proclaimed it was as close as he could get it, and the bike idled at 1500 rpm. But to his credit, he was following the BMW factory guidlelines, which means don't mess with the preset screws.

    With Paul Glaves guidance, and some patience, I was able to get my bike to idle out at just over 1000 rpm just fine, using my mercury tubes. Later when working at the same BMW dealer where the Service Manager said I screwed up the TBs, I balanced the TBs myself, with a bit of help from the same Service Manager, using the very accurate BMW tester, and I was within 1/2 milibar accuracy. I recently rebuilt both TBs using the Bing kit, and I again was able to get it right into a smooth balanced idle at 1050 rpm.

    Visual sighting through the TBs to set up the closed plate position is only good for initial running setup. You still need a manometer of some type to accurately set the balance.

    The TPS setting is also key to getting the bike running right. This too, you cannot simply "eyeball" or line up to match marks for proper running. You'll need to use a good VOM, probe the red/white wire at the TPS connector, and to ground on the engine, and set the TPS in the idle position at 370 millivolt. I set mine a fuzz higher at 400 because I have a freer flowing exhaust and Techlusion, along with a K&N filter in the airbox. I still get 42 to 45 mpg regularly. If you eyeball the TPS position, you'll very likely end up with a very rich running bike that gets mileage well below 40 mpg. This I know from direct experience.

  10. #10
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    I think I got everything set up, though the bike idles at 1500 rpm once warm. I haven't checked timing yet, but the throttle body balance is as close as I can get it for now seeing as the right TB shaft is shot. Valve lash is set at .015 and .030mm intake and exhaust, oil is new, oil filter is new, air filter still needs replacement and probably the airbox rubbers as well. Plugs need to be replaced as well. I did the zero = zero adjustment (the TPS was way off) as best I could and I may pull the cat code plug (the TPS adjustment led to more popping, surging is about the same). Both TBs need a good cleaning.

    The joys of the $500 GS.

  11. #11
    Curmudgeon nrpetersen's Avatar
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    Quote Originally Posted by dumptruck View Post
    I think I got everything set up, though the bike idles at 1500 rpm once warm. I haven't checked timing yet, but the throttle body balance is as close as I can get it for now seeing as the right TB shaft is shot. Valve lash is set at .015 and .030mm intake and exhaust, oil is new, oil filter is new, air filter still needs replacement and probably the airbox rubbers as well. Plugs need to be replaced as well. I did the zero = zero adjustment (the TPS was way off) as best I could and I may pull the cat code plug (the TPS adjustment led to more popping, surging is about the same). Both TBs need a good cleaning.
    I hope that is .15 & .3 mm valve lash.....

    You have a leaky intake system, throttle shaft or bushing wear, insufficient throttle cable clearance, or improperly set throttle position stops if you can't get the idle rpm down
    Retired w 2005 K1200LT, 2000 R1100RT, & 1975 R90/6

  12. #12
    Day Dreaming ... happy wanderer's Avatar
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    Dealers and mechanics like the ones ANDYVH describes are the reason I try to fix my own bikes in all cases unless it is something that requires expensive special tools or a machine shop etc. If the screws have never been touched and you are happy assuming BMW did them perfectly at the factory then do it Paul Glaves way.

    If not, like after a rebuild or if you cannot achieve a proper idle after checking everything else, Mr. Lentini's approach to setting up throttle bodies from scratch makes total sense to me. By backing off the idle set screw completely and setting the TPS at just over 0VDC (6mV) you KNOW you are at zero when you lock it down. Then by turning the lock screw in till you are at .370 you KNOW you are at the correct idle setting (or very close to it). Just like the factory did with a different tool (a flow meter), that's all. Who has a flow meter handy?

    In my case I had to back the left throttle lock screw off to a 0.345 VDC TPS reading to achieve 1100RPM idle after opening the big brass screws 1.5 turns and re-balance the right side accordingly. I did all this with the big brass screws turned all the way in to make sure they did not introduce another factor, then turned them out again once perfect idle balance was set. I think my TPS setting is a tad low simply because it is a 14 year old potentiometer and they have some variance as they age much like the goof turning the screw! This it true of any resistor or capacitor or old guy like me.

    Once the left side is set up you just balance the other side to be identical. You now have perfect idle balance and as Paul stated, you just need to synch slightly off off idle so the tension on the cables is identical for both sides using your favorite vacuum balancing. Works like a charm. I cannot understand why a BMW shop would not do it this way. It is fast, it is easy and it works. Every time.

    nrpetersen, I have no idea what delta P in the intake manifold being used as a matching flow measurement device means but even if I did there is no way I could measure it with the tools most of us typically have in our workshops. I am also sure I could never set up the correct gap in the throttle plate by eyeballing it. But using the TPS and a good Fluke voltmeter with known set points did the job perfectly.

    +1 on what npeterson just wrote. Until the vacuum leaks caused by the bushing or shaft are fixed I highly doubt the bike will ever idle or run smoothly when you pull that throttle. I bet once the throttle bodies are fixed and you get it set up right that GS will run just fine!

    OH.. I think you meant valve _clearance_ Valve lash refers to rocker arm spacing and should be set before you set the valve clearance.
    MJM - BeeCeeBeemers Motorcycle Club Vancouver B.C.
    '81 R80G/S, '82 R100RS, '00 R1100RT

  13. #13
    Curmudgeon nrpetersen's Avatar
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    My delta P device is just a U tube etc like everyone else. Carb Stix etc would work too.

    Setting the final LH throttle stop position using the TPS is asking a lot from the electrical specs of the TPS (which I saw somewhere) I think I can do just as well visually, and in my (etc) method it doesn't make any difference, since the throttle stops are only preset to get the engine running in a reasonable way. The throttle stops are readjusted later with a standardized BBS opening (1 1/2 turns) to get proper balance and idle rpm. Only then is the TPS set to 375 mv. and only then are the BBS tweaked a little for desired idle and balance.

    Valve lash = valve clearance to me. May be an age thing here too at 72 - today!

    Intake valve clearances may be very critical. I spent most of my time on this. The rest of it took only maybe 20 minutes.
    Retired w 2005 K1200LT, 2000 R1100RT, & 1975 R90/6

  14. #14
    Day Dreaming ... happy wanderer's Avatar
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    Hey, whatever turns your crank! I followed the zero-zero procedure (several times) and can say with certainty that it works. Your application may vary.. all standard disclaimers apply.

    I was confused by the term "Delta P device" so I googled "delta P" and it means pressure differential. So a "delta P device" is a pressure differential tool. For our bikes that would mean a TwinMax, or CarbStix or CarbTune (my favourite) or one of many other homemade gadgets.

    I had never heard carb balancers referred to that way. A bit overly scientific for my basic mechanical skills I guess.

    It also dawned on me that dumptruck's real problem might be found simply by spraying some WD40 or throttle body cleaner around the throttle body shafts etc. with the engine running and looking for vacuum leaks first and then do the adjustments after fixing the leaks if any were found.
    MJM - BeeCeeBeemers Motorcycle Club Vancouver B.C.
    '81 R80G/S, '82 R100RS, '00 R1100RT

  15. #15
    Nickname: Droid
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    I need to clarify my experience with the local BMW shop service manager. I don't want him mis-read as one of those stubborn service guys that only goes exactly by the BMW book with no open mindedness. He set the TBs on my bike "as close as possible" after I had messed with the screws, but trying to stay within the BMW technical guidelines. He also sees a LOT of the misguided online directions many people apply to their bikes and mess them up.

    At the time I didn't know the method Paul Glaves describes, and I found out the service manager didn't either. The service manager knew nothing of my wrench abilities at the time and he has seen PLENTY of messed up bikes that run like crap at the hands of their inept wrenching owners. So his point of view was biased by his experiences.

    Over time, he and I got to know each other, and he got to know that I have some mechanical abilities. I then started working part time at the dealership, with some minor wrenching in the shop alongside him. I kind of proved myself, and he saw the method described here worked well enough that he worked with me on my bike to get it set up right. Now after installing the Bing TB kit on my bike (1st one in the shop) he has asked me about the Bing TB kit installation and results being done on another bike at the shop. I am NOT saying any of this to pat myself on the back, but to say that he is not the one-minded type when he sees some real proof of things that work.

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