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Thread: Bing 32 (11/12) question

  1. #1
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    '75 R90/6 - Bing 32 (11/12) question + timing issue

    Hi,
    I'm in the process of sorting out my '75 R90/6 and I'm doing a basic clean and rebuild of the carbs. Once I got into it I noticed that my carbs do not have an external choke return spring. Also in the bowl I discovered that neither float had a "hairclip" retainer (the fine wire that connects the float-bowl tang to the float needle). Just wondering if these are in fact missing or if it is just a model variation? Thanks...
    Last edited by sprouty115; 10-14-2017 at 01:03 PM.

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    Liaison 20774's Avatar
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    Welcome to the forum! My 19/20 carbs don't have any return spring for the choke...the choke position is physically changed by moving the handle on the engine under the tank. Not sure if that's the spring you're talking about. There may be a small spring inside the choke assembly, but that's there probably for taking up any slop.

    As for the small hairclip retainer, according to the Bing manual, the type 64 carbs don't have that, but the 64-2 and 64-3 carbs indicate they were used. It's there for a more positive pull down of the needle valve...I suppose it could be useful. I don't recall if my /7 carbs (also 64s) have them or not, but I haven't had any issues that I could attribute to that.
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    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

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    ABC,AMA(LIFE),MOA,RA,IBMW MANICMECHANIC's Avatar
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    What Kurt said. The "choke" (enrichener) on your bike is operated by a very stiff wire, which gives positive operation, so no return spring is needed. Just ensure they are set up properly, so they are OFF fully.
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    Airmarshal-IL James.A's Avatar
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    Return springs on enricher levers are associated with later models with the choke actuating lever on the handlebars. The little spring/bale on float needles are employed to help keep the needle placed correctly on the float tab. It is probably every kind of wrong, but, I have never worried about those little retainers being missing in any of the airheads I have owned.
    1973 R75/5

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    Thanks for the the info. I got a little confused by the images I was running across while looking for the rebuild kit. This is my first airhead (after wanting one for decades), and I have to admit there is a bit of a learning curve - my most recent rebuilds have been 2-stroke RD 350/250's and those bikes are as simple as they get.

    BTW, the bike has about 13K original miles (based on service records and the general condition of the bike), and it doesn't look like it's been molested, but I'm still surprised by what I'm finding after I was told the bike was in for a service 5-months ago: missing spring on on idle adjustment screw, main needles in different positions (one was in the 1st notch, the other was in the 4th), carbs wildly out of balance, valve clearances set to opposite specs, points settings well out of spec.

    I wanted a project bike, so I'm looking forward to working on it, but it just struck me as odd that some basic things were so far out of whack...

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    ABC,AMA(LIFE),MOA,RA,IBMW MANICMECHANIC's Avatar
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    One of the best things you can do is join up with the Airheads (MOA 214) They are people who own and care for the bikes and have a passion for keeping them running. You didn't say where you're from, but there are often Airhead tech days around, just to keep the info flowing and the bikes running.
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    Quote Originally Posted by MANICMECHANIC View Post
    One of the best things you can do is join up with the Airheads (MOA 214) They are people who own and care for the bikes and have a passion for keeping them running. You didn't say where you're from, but there are often Airhead tech days around, just to keep the info flowing and the bikes running.
    Thanks, as it turns out I joined a few days ago. And I'm in Rhode Island - definitely looking forward to upcoming events.

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    One more follow up question - my bike came with a grommet installed at the air filter housing and suction funnel connection point, but it doesn't show up on the microfiche? There is one showing for the carb/suction funnel side (#10), but not the other end? Any thoughts?
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    Airmarshal-IL James.A's Avatar
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    There are some who would tell you that a parts fiche is not an assembly diagram in the strictest sense. Based on the parts fiche, #10 is the rubber sleeve that seals the air tube to the carburetor. I am going out on a limb here, but the #15 looks like a stiffener that would go inside the air tube where it fits into the rubber sleeve. These type of devices provide a solid base for the ribbon clamp to squeeze on. No airhead I have ever owned had a stiffener at the carburetor end of the air tube. I have found them inside the tube on the air filter end of bikes with the later square-ish, plastic air filter box. In fact, the stiffener is essential in that position on that style of air filter housing.

    #20 on this parts fiche would be an O-ring that goes on the outside of the stub of the aluminum air filter housing. There might be a little groove in the stub for the O-ring. On the air filter end, the air tube slides directly on to the stub and the ribbon clamp seals it off. That is what the O-ring is for.
    1973 R75/5

  10. #10
    I see them assembled different ways but as far as I know, the correct way is pretty much as that diagram shows it, with the top of the elbow clamping directly to the airbox and the bottom of the elbow using the 395 rubber sleeve (it has a stepped ID) to join to the carb.

    That said, there is an R90/6 at my house that is assembled in the later style, with the sleeve at the top. I haven't looked to see why it is that way but it's on my to-do list as this is part of a new web page I'm working on. It could be that parts got changed over the years and this is what works best with the updated parts. Some of the old components are NLA.

    I think that round part is the stiffening sleeve that is found in one end of most elbows but is not available separately. Many elbows I see are missing them. They are used where a rubber sleeve clamps over the end of the elbow, which is the bottom of the earlier (26mm, 32mm, R90S) elbows and the top of the later (40mm and R65) ones. With the square airbox they all clamp at the top.

    The intake tract evolved over time, with several improvements being made from the R75/5 to the '81-on bikes.
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    Quote Originally Posted by James.A View Post
    There are some who would tell you that a parts fiche is not an assembly diagram in the strictest sense. Based on the parts fiche, #10 is the rubber sleeve that seals the air tube to the carburetor. I am going out on a limb here, but the #15 looks like a stiffener that would go inside the air tube where it fits into the rubber sleeve. These type of devices provide a solid base for the ribbon clamp to squeeze on. No airhead I have ever owned had a stiffener at the carburetor end of the air tube. I have found them inside the tube on the air filter end of bikes with the later square-ish, plastic air filter box. In fact, the stiffener is essential in that position on that style of air filter housing.

    #20 on this parts fiche would be an O-ring that goes on the outside of the stub of the aluminum air filter housing. There might be a little groove in the stub for the O-ring. On the air filter end, the air tube slides directly on to the stub and the ribbon clamp seals it off. That is what the O-ring is for.
    Quote Originally Posted by AntonLargiader View Post
    I see them assembled different ways but as far as I know, the correct way is pretty much as that diagram shows it, with the top of the elbow clamping directly to the airbox and the bottom of the elbow using the 395 rubber sleeve (it has a stepped ID) to join to the carb.

    That said, there is an R90/6 at my house that is assembled in the later style, with the sleeve at the top. I haven't looked to see why it is that way but it's on my to-do list as this is part of a new web page I'm working on. It could be that parts got changed over the years and this is what works best with the updated parts. Some of the old components are NLA.

    I think that round part is the stiffening sleeve that is found in one end of most elbows but is not available separately. Many elbows I see are missing them. They are used where a rubber sleeve clamps over the end of the elbow, which is the bottom of the earlier (26mm, 32mm, R90S) elbows and the top of the later (40mm and R65) ones. With the square airbox they all clamp at the top.

    The intake tract evolved over time, with several improvements being made from the R75/5 to the '81-on bikes.
    Ah, I didn't understand what part #15 was. Let me go see if I can find a stiffener in the elbow, I didn't think to look inside. I'll post back later. Thanks for the help.

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    So after looking over what I had, reading the posts above and from talking to the parts guys at Max BMW, it sounds like the parts I have are OEM and I'm not missing anything.

    BMW R90 - carb elbows.jpg

    It does appear however that due to the age of the bike and the condition of the material that it might be a good idea to replace a few things. So that is in process right now and I should have it all back together by next week.

    EDIT to add: those parts may not be assembled correctly, as I just sort of positioned everything for the picture. But I did learn from the parts guys at Max BMW that the Elbows are are correctly assembled when they are on their respective sides (easy to tell by the different bends) and the "small slit" at the end of the elbow is facing up (not shown above).
    Last edited by sprouty115; 08-25-2017 at 12:32 PM.

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    So carbs are all rebuilt but I have a question - can someone explain the correct position for the choke lever (on the side of the carb) in both the off position and the on position?

    I ask because after the rebuild as I was trying to sync the carbs I noticed that by turning the the idle screw all the way in the bike would continue to increase the idle speed (sometimes as high as 2500 rpm). A little search on the forums and on youtube told me that that is incorrect and that I still have some circuit feeding gas to the engine. Considering that the insides all looked good after a thorough cleaning and the gaskets o-rings were replaced I decided to look at the choke (enricher). It occurred to me that I had arbitrarily set the choke levers on the carb bodies to be parallel to the carb body while the choke lever near the tank was fully up (off). This was how they were set when I bought the bike and I assumed this was correct. So I loosened the lock screw and slid the levers on the carbs down and as far as I could and then tightened the lock screw on the choke wire.

    This allowed me to turn the idle screw in and see the reduction of rpm that I was expecting and then set the idle circuit so that the bike would idle smoothly. Right now it seems to be running well, but I'd prefer to know I was setting the bike up properly and not masking an issue caused by an incorrectly adjusted or assembled choke (I only removed the chokes from the carb bodies and didn't completely disassemble them, but they may have been incorrectly assemble previously).

    Other pertinent info:
    - 1975 R90/6
    - points gapped to .4mm
    - valves set to .10mm Intake, .20mm Exhaust
    - Bing 64/32/11&12 carbs
    - float bowl fuel level set to 24mm
    - throttle cables set to 2mm free-play
    - main needle set to position #2
    - new gaskets, orings, rubber grommets (carb to head and elbow to airbox), new elbows
    - bike was fully warmed up during tuning

  14. #14
    Liaison 20774's Avatar
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    When choke is off, the arm of the hand choke lever is up and parallel to the ground.
    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!

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    Quote Originally Posted by 20774 View Post
    When choke is off, the arm of the hand choke lever is up and parallel to the ground.
    Just reread your reply - sorry, I may not have been clear:
    with the hand choke lever up (parallel to the ground) where should the carb levers be?

    With my bike when they are adjusted to be parallel to the ground (with the hand choke in the off position) the bike stumbles and dies. But when I adjust them to be pointed down with the hand choke lever off the bike appears to run better.

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