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Thread: When to rebuild Bing carbs on an airhead?

  1. #1
    Registered User will.kraham's Avatar
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    When to rebuild Bing carbs on an airhead?

    Should be done how often? And what about 10% ethanol gas - does this increase frequency of rebuild? R80 is hard to start but once warmed up idles and runs fine.

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    Administrator 20774's Avatar
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    Will -

    Welcome to the forum! Do you have a twin shock R80 or is it one of the 1985-on bikes? Not that it makes much difference regarding your question.

    Personally, I don't find that the ethanol affects or dictates when I need to rebuild the carbs. You will hear/read that the deposits it leaves and the fuel hoses deteriorates quicker, but I really haven't found that it has changed this drastically for me.

    I let bike performance tell me when the carbs need to be looked at. Hard starting is a sign and you might be able to improve that with a general clean up of the carb interior. Be sure that the bike is in tune and that the valves are properly set...valves that are "tight" can make the bike idle roughly and also make for hard starting. There is a choke (really an enrichener) that aids with starting...could be that this needs to be refurbed as well.

    I monitor my gas mileage on each tank and over time, the trends of that can tell me if something is off. I also would look at throttle performance and see if the response is changing over time. These things could signal a need to rebuild the carb.

    The ethanol can have a detrimental effect on the floats. I've not noticed huge changes in the intervals they need to be changed...I usually do it since I can't remember when the last time it was. But mileages of say 25-40K might be appropriate intervals to consider changing the floats. Or maybe it's a time frame if you don't ride that much...maybe every 5 years? Maybe a similar situation with the carb diaphragms.

    So, my approach is if there's nothing obviously wrong, I worry about other things. But monitor the bike/carb performance and go from there.
    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
    I monitor my gas mileage on each tank and over time, the trends of that can tell me if something is off. I also would look at throttle performance and see if the response is changing over time. These things could signal a need to rebuild the carb.

    So, my approach is if there's nothing obviously wrong, I worry about other things. But monitor the bike/carb performance and go from there.
    Just for kicks, what mileage do you get? I have found that with all the changes I have done, with carbs, riding style, pulling trailer or not, my mileage doesn't perceptibly change. Always around 40 mpg.

    I haven't seen any issues with ethanol (around 10% or less listed on various pumps).

    However, I do run Lucas gas additive which adds upper end lube, but it also (I hope) does some cleaning in the carbs and helps keep them clean and injectors too! Oops, I made a mistook, we don't have injectors!
    "The difference between death and taxes is that death doesn't change every time congress meets." - Will Rogers

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    Administrator 20774's Avatar
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    Quote Originally Posted by jimmylee View Post
    Just for kicks, what mileage do you get? I have found that with all the changes I have done, with carbs, riding style, pulling trailer or not, my mileage doesn't perceptibly change. Always around 40 mpg.
    Early on, I was getting 45+ with swings into the 50s especially when traveling at constant speeds when on longer trips. Then it began to settle more around 40 but again with swings from the upper 30s to mid 40s depending on the type of riding. I'm only averaging 3-4K miles per year over the past 10 years...I have acquired the other bikes in that time frame.

    I attribute the lowering of the gas mileage over time to the wearing or loosening of the engine. Since I just rebuilt the top end, I'll be interested to see how things change going forward.
    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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    Hard to start issue is most likely valves are too tight - check those first.
    I have found, if you use black rubber fuel line, especially the cloth covered stuff, the ethanol really eats it up, cracking the lines while leaving black goo in the carbs. Now I am using some synthetic gray fuel line, and problem has gone away.
    The ethanol is bad for the floats- I minimize this by shutting fuel off about a mile out from home - YMMV

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    Quote Originally Posted by jforgo View Post
    Hard to start issue is most likely valves are too tight - check those first.
    I have found, if you use black rubber fuel line, especially the cloth covered stuff, the ethanol really eats it up, cracking the lines while leaving black goo in the carbs. Now I am using some synthetic gray fuel line, and problem has gone away.
    The ethanol is bad for the floats- I minimize this by shutting fuel off about a mile out from home - YMMV
    When you say, "black rubber fuel line, especially the cloth covered stuff." Do you mean the stuff sold by BMW?

    Also, the above fuel line, how long did the line last before the ethanol started to break it down? How often did you change the fuel line? I have heard that the line sold by Max's which is supposed to be the BMW stuff, and was said to last 3 or 4 years. Hmmmm?

    I've had my new line on now for about 11 months, and with the see through in-line fuel filters and nothing in the filters to indicate any problems . . . yet!

    I was figuring on replacing once per year, but I am thinking on only doing the short section just under the petcock since that is the section I disconnect when I take off the tank and the top gets kinda ragged looking.
    "The difference between death and taxes is that death doesn't change every time congress meets." - Will Rogers

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    Day Dreaming ... happy wanderer's Avatar
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    I've given up on the BMW cloth braided rubber fuel line. It does seem to deteriorate quickly now that ethanol is harder to avoid. I picked up a couple of lengths of BAI alcohol resistant fuel line from the Bing Agency booth at the MOA rally last July. They were selling lengths long enough to do up any twin petcock airhead for $11. A bonus with this line is no clamps required. Simply push it on and it seals extremely well to a barbed fitting. Bing had it in black or blue which was sort of see through. I went with black but having second thoughts now. See through fuel line is useful in some cases. My left hand petcock gave me suspicions of not flowing well yesterday as a fer'instance. Anyway... there is no real info on the Bing site on the fuel line but turns out it's apparently for aircraft applications. Info here for anyone interested: http://www.aircraft-spruce.com/catal...s/bingfuel.php

    Or just google "BAI alcohol proof fuel line"
    MJM - BeeCeeBeemers Motorcycle Club Vancouver B.C.
    '81 R80G/S, '82 R100RS, '00 R1100RT

  8. #8
    Monza Blue 1974 R90/6
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    As a cautionary tale on the BAI black line from Bing - I renewed mine in the spring of 2012 and in the middle of this summer (2013) had a catastrophic failure just above the right carb. Line split and fuel was gushing out. Lucky I was in town and noticed while stopped at an intersection and also lucky I had a spare length of line in my on board stash or I would have been stranded. When I got home and checked the rest of the line sections, all were brittle. Approx 15 months doesn't seem acceptable for "alcohol proof" line. I sent split section back to Bing and asked for refund but have not received a response. Since then I have read reports on other forums/lists about similar problems with the BAI line.

    Barron

  9. #9
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    I just finished a carb rebuild on my RS...new gaskets & o-rings & diaphragms, new floats & float needles, new slide needles & jets, and a thorough cleaning. There's just over 49k miles on the bike and I can't be sure but I suspect it was the first time they've been done (I bought it about 18 mo. ago with 46k on it). They were pretty grungy inside, esp. the enricheners. The diaphragms seemed really thin & fragile & the right one had a large tear in it but I think it happened on removal. The o-rings were pretty bad, too...they all pretty much disintegrated on removal. The bike starts & runs a lot better now. It was running out of oomph around 4k rpm but now pulls strong up to about redline. I also replaced the throttle cables while I was at it. It really makes a big difference, it's like a different bike. Well worth the hassle & expense.
    1983 R100RS (Sold)
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    Quote Originally Posted by jimmylee View Post
    When you say, "black rubber fuel line, especially the cloth covered stuff." Do you mean the stuff sold by BMW?

    Also, the above fuel line, how long did the line last before the ethanol started to break it down? How often did you change the fuel line? I have heard that the line sold by Max's which is supposed to be the BMW stuff, and was said to last 3 or 4 years. Hmmmm?

    I've had my new line on now for about 11 months, and with the see through in-line fuel filters and nothing in the filters to indicate any problems . . . yet!

    I was figuring on replacing once per year, but I am thinking on only doing the short section just under the petcock since that is the section I disconnect when I take off the tank and the top gets kinda ragged looking.
    The stuff I had lasted less than a year. I am not certain where I bought it. The gray stuff I got from the local ex Guzzi dealer. The filters didn't show the black goo, but it sure got in carbs. I suspect the rubber is in a dissolved state going thru the lines, then precipitates in areas of the carb. Also, most of the fuel lines are past the filters anyway.

  11. #11
    Registered User lkchris's Avatar
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    No clamps have ever been required when specified size (metric) fuel line is used.
    Kent Christensen
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    '12 R1200RT, '02 R1100S, '84 R80G/S

  12. #12
    Registered User lkchris's Avatar
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    Know that needles wear and should be replaced periodically.
    Kent Christensen
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    '12 R1200RT, '02 R1100S, '84 R80G/S

  13. #13
    Registered User will.kraham's Avatar
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    Getting 45 mpg. 30 year old bike and valves are in spec, carbs likely never been opened. Other rubber parts have given up the ghost - final drive seal, gearbox seals, pushrod tube seals, so seems reasonable that rubber parts in carb might need replacing. Anyone use Lucas ethanol fuel conditioner with stabilizers? Claims to help prevent varnish and gums. 1 oz treats 5 gal.

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    #4869 DennisDarrow's Avatar
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    On a regular basis as I bring in 5 gallon cans of fuel onto the place I treat them right then so there is NO question if the fuel has been treated. For gasoline in goes a dose of Lucas Injector/Carb fuel cleaner treatment, stabil, or Startron, and some Marvel Mystery stuff. For Diesel I put in Lucas as with gas, Cetane, and Marvel...........Each individual machine gets a dose of something if it needs it. My chipper, a heavy duty B&S Vanguard engine, came back from my son's with a barely staying running/idling miss. After now a couple of doses of heavy duty Lucas it is back to sounding like a well tuned Harley at idle. The generator for total loss electrical backup gets a dose of Startron as you can't overdose it to much and it sits and sits for months at a time. The Honda 3000 genset for the Airstream, gets a dose of lucas as it is a Honda and they tend to get crud in the float bowls. Had to replace the whole carb with my Honda engine pressure washer due to the float bowl being one solid bunch of white crud. lolol.......my old Troy Bilt Horse tiller with umpteen million hours on it gets not only a fuel dose treatment but every known oil treatment to keep the piston ring blowby and smoking down to where it is tolerable................
    The R90 is just another dose of Lucas, octane boost, and stabil. For the winter I fill it up with ethanol free ethyl (high test), take the bowls off and sit them on top of the cylinder, and then when I feel like going for a ride in the winter I might dump in some Lucas; but typically just get on and ride..........
    All ..........ALL of my engines have a fuel shut off, petcock, and are run until they quit running and then if they have an easily accessable float drain, that is done also. I always get let's say a spoon full of fuel out when I do that............God bless.....Dennis

  15. #15
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    Quote Originally Posted by lkchris View Post
    No clamps have ever been required when specified size (metric) fuel line is used.
    What is the specified metric ID for the fuel tubing?
    "The difference between death and taxes is that death doesn't change every time congress meets." - Will Rogers

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