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Thread: Float Level

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    Float Level

    Just rebuilt carbs on my 78 R100 . So what do I set the fuel level to? 1/2" from top of bowl?

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    Administrator 20774's Avatar
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    According to Snowbum, for the 32mm carbs it should be a fuel height (or depth) of 24mm. I'm not sure what that works to be when measured from the top.
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    '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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    According to the Airhead Guru in our club, the float level should be set to the fuel shuts off exactly when the float metal arm is perfectly parallel with the bottom of the carb where the float bowl attaches to the carb.

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    Quote Originally Posted by JIMMYLEE View Post
    According to the Airhead Guru in our club, the float level should be set to the fuel shuts off exactly when the float metal arm is perfectly parallel with the bottom of the carb where the float bowl attaches to the carb.
    This has always been the suggestion as far back as I can remember...it's in my Haynes and/or Clymer manual. But what this assumes is that every float is exactly the same and works the same way. Rather than make that assumption, it's best to use the height of fuel as your guide. The "parallel" method might be a good starting point, but in the end, you want the right around of fuel in the carb so that the ability of the venturi effect in the throat of the carb pulls up the proper amount of fuel. If the fuel level is too low, the venturi has a harder time drawing the fuel up...the bike runs lean. If the fuel level is too high, the venturi can easily suck up the gas...the bike runs rich. The fuel height is what you want to shoot for.
    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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    Bing carb problem

    This is a perfect place for me to chime in a question or two!

    I purchased an 1978 R100/7 just before Christmas, so I don't have a lot of personal history pertaining to its reliability.

    However, I have had this recurring problem that baffles me. My right carb goes into "flood" mode from time to time - three times on the several rides that I have been on. I have completely drained the tank removed both petcocks, and cleaned out thoroughly. Replace all fuel hose with brand new, and then also installed 1 on each side of an in-line fuel filters recommended by Max's BMW. Thought I had the problem fixed until yesterday evening. I took the bike on a 130 mile trip to see my daughter and about 2 miles from her house, the engine starts to gurgle on the right side only. At slow speed and in her driveway, fuel pouring out of right carb.

    This morning I got up - pulled off the fuel bowl - some dirt in there, dumped, cleaned, thought was fixed. I manually raised lowered the float, and it shut off perfectly. 10 minutes later on the way - same thing. Did the same thing again. About 20 minutes later -same thing. Repeated procedure. Then rode 100 more miles home at pretty high speed, 4th gear to keep the engine revs up around 4500 to 5000 and seemed to run fine - I didn't want to slow down to find out if flooding was ok or not.


    If this is due to dirt, why not both carbs?

    This bike was supposed to have had new floats installed last year so I assumed that they were the "new style" that resists the new methanol used by some fuel suppliers.

    (1) How does one look at the floats and know for sure if they are the new style? What color was the old style? I heard that the new style is white, but is that pure white or an off-color white?

    (2) Other brands of carbs actually sell "needle and seats" as sets. Does this 34mm Bing sell the seat? I know the needles are available now with a rubber tip. Is that the best or something else?

    (3) I read somewhere where one can test the floats for reliability by putting them in a bowl of something or other. And watching them to see how they float. Has anyone ever heard of this testing procedure and has anyone done this and is this test reliable?

    Thanks for your input.

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    JimmyLee -

    What might be happening is that the float is sticking...it can't ride up and down freely and thus sticks open. It's important that it must easily float up and seal against the seat. Double check the range of motion.

    1) Float types -- AFAIK there are only two types. The white floats which are not immune to soaking up fuel over time...they are connected by the metal tang and pivot about the pin. Bing used to make a gray colored float of the same design as the white which was immune, but at a rally a couple of years ago, I asked where they were in their inventory. They discontinued them because they couldn't be manufactured well and were falling aprt. The second type of float is the independent float where each floats up and down on separate vertical pins. In addition, you have to change float bowls to use these. When going to these types of floats, giving up the float bowl means you give up the overflow tube. Could be a problem if there's no way for the gas to escape if it needs to.

    2) Bing does sell seats. They have to be carefully removed from the body of the carb using drill bits, etc. I know Bing can replace them easily. If the seats might be a problem, use a wooden dowel with a small amount of abrasive, even toothpaste, on the end and burnish the seat to take out any slight imperfections.

    3) Oak has suggested that if a float has about 1/3 about the fuel line in a container of gas, that's about right. Snowbum has done some testing on floats sent to him by other owners. His information is discused here:

    http://bmwmotorcycletech.info/bingcv.htm
    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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    Quote Originally Posted by 20774 View Post
    This has always been the suggestion as far back as I can remember...it's in my Haynes and/or Clymer manual. But what this assumes is that every float is exactly the same and works the same way. Rather than make that assumption, it's best to use the height of fuel as your guide. The "parallel" method might be a good starting point, but in the end, you want the right around of fuel in the carb so that the ability of the venturi effect in the throat of the carb pulls up the proper amount of fuel. If the fuel level is too low, the venturi has a harder time drawing the fuel up...the bike runs lean. If the fuel level is too high, the venturi can easily suck up the gas...the bike runs rich. The fuel height is what you want to shoot for.
    How does one measure? If "from the bottom" mean when you measure the fuel left in the bowl after letting in the fuel and detaching bowl from carb, carefully not dropping any of the fuel out, does one measure the depth from the bottom of the bowl up to the level height making sure that the bowl is being held perfectly level?

    Also, doesn't this method have a flaw also? In that it assumes that volume of displacement of the floats is the same? The weight (or mass) of the floats in theory could be different too.

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    Turn petcocks on for 5-10 seconds, then turn off. Remove the float bowl. Easy enough to do without spilling fuel. As best you can, just hold the bowl level and stick in a rod or dowel and then measure the wet section on the rod/dowel...better if you have a small metal ruler. The measurement is done in the very center...there should be a small well in the bottom. There is some fuel that will drain into the bowl after the petcock is shut off...it's the amount that is below the petcock and still in the hose. Probably not that significant, but you could either pinch off the fuel hose (it gets damaged internally if you do that) or just pull it off and catch that fuel in a separate container.

    If the float completely sinks so that nothing is above the height of the fuel, that results in a situation where setting the float height is going to be near impossible...obviously, the float must be replaced. If the float does in fact have some bouyancy, then it will eventually float up and seat thus cutting off fuel flow. The amount of fluid displaced will equal the weight of the float. With it floating some, the tang on the float can be adjusted such that the fuel will shut off with the right amount of fuel in the bowl. But I suppose that poor float might have the tang bent to an extreme angle whereas a good float would have the tang only slightly bent. But wouldn't the fuel still be right in each bowl? Not a situation that you might want, but seems like it would work in a pinch.
    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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    Quote Originally Posted by dougjordan View Post
    Just rebuilt carbs on my 78 R100 . So what do I set the fuel level to? 1/2" from top of bowl?
    Bottom of bowl{center} to top of fuel 24mm = 5/8 " top of bowel to top of fuel. To my eye when checking float, fuel shut off when level.I think Im close to being set. Thanks all for input.

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    Kurt,

    Gotcha.

    Thanks for your thoughtful and patient answers.

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    All of the above and with KURT on pretty much everything. Especially the sticking float that is perhaps a bit cocked or something on the pin that it rides on. A bit of dirt can easily do this also by holding the needle open enough to cause problem. Yes, this can and does happen on one side and not the other. Are you SURE that the leak is coming out of the bowl and not a fuel line????.........Easy for the lines to deteriorate and LOOK like the bowl but in actuality it is a fuel line. Then, when foooling with the bowl one nudges the line just enough to stop the leak and NOT see it or notice it is a fuel line. Just a thought....it does happen.....like the other day when I fired up the bike after it setting for a month. The fuel line from the "t" to the carb was split where it attaches to the carb.........Replacement time, not just wiggle it till it stopped leaking, which for me, usually works.
    Also.........If I am gonna not ride for a week or two or MORE I take the bowls off and sit them on top of the cylinder. Seems, at least to this ol common sense guy, that the floats dry out and dont give me problems. I have 2 sets of floats that are both pretty ancient and when one gets heavy enough to cause problems, I change them out and let them dry a few months or a year and then use them again......WHO knows???.....For me, it works.........God bless........Dennis

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    Quote Originally Posted by DennisDarrow View Post
    All of the above and with KURT on pretty much everything. Especially the sticking float that is perhaps a bit cocked or something on the pin that it rides on. A bit of dirt can easily do this also by holding the needle open enough to cause problem. Yes, this can and does happen on one side and not the other. Are you SURE that the leak is coming out of the bowl and not a fuel line????.........Easy for the lines to deteriorate and LOOK like the bowl but in actuality it is a fuel line. Then, when foooling with the bowl one nudges the line just enough to stop the leak and NOT see it or notice it is a fuel line. Just a thought....it does happen.....like the other day when I fired up the bike after it setting for a month. The fuel line from the "t" to the carb was split where it attaches to the carb.........Replacement time, not just wiggle it till it stopped leaking, which for me, usually works.
    Also.........If I am gonna not ride for a week or two or MORE I take the bowls off and sit them on top of the cylinder. Seems, at least to this ol common sense guy, that the floats dry out and dont give me problems. I have 2 sets of floats that are both pretty ancient and when one gets heavy enough to cause problems, I change them out and let them dry a few months or a year and then use them again......WHO knows???.....For me, it works.........God bless........Dennis
    The fuel lines are brand new, less than a few hundred miles. I purchased from Max/s BMW a month or so ago.

    Also, when I take the bowl off, and just check, allowing some fuel to run through and "clear the shut-off" it stops, at least for a while. It has been a few weeks since it last happened until yesterday. I would think if it were fuel line, my remedy wouldn't change anything and leak wouldn't have stopped at all.

    I am going to try next to take off carb, and test the float in a bowl of fresh gasoline to see how much, if any, stays afloat when put in there.

    I am pretty sure that the float is not binding up - it is totally free on the pin, and is also so when I try to slide it from one side to the other to see if I can find anywhere where movement is impaired by anything. The only thing may be, that there is some way the bowl, when put back on, will cause some sort of binding.

    The previous owner said he replaced the floats about a year ago. My floats do look rather new, and undamaged.

    The other thing I want to do is closely inspect the float needle to see if it has a wear spot/circle on it. I will also try to "resurface" needle seat by polishing as suggested by Kurt.

    Years ago, when I worked at the Honda dealership (which at the time sold a new BMW or two a year!) we used to be able to purchase a new needle & seat for the Kei-Hin (sp?) carbs very cheaply - easy to replace for a buck or two. But with these Bings, no easy way to replace seat.

    Sometimes, I think Bing enjoys shooting itself in the foot. Other manufacturers produce some superior products, but Bing somehow likes to stay in the dark ages. I think back to the Bings on my R50/2. There were junk from the factory - and the carbs of the same era (esp. Mikunis) were light years ahead of Bing.

    On my R90/6, however, the Bings never gave me an ounce of trouble. I did a minor rebuild on them at the time (circa 1990) by replacing the diaphragms and the needles. Never once had a problem!

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