Starting gremlins with Bing variations

Discussion in 'Airheads' started by headtube, Apr 27, 2013.

  1. headtube

    headtube 6 mesas de invierno!

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    My 79 RS is running great, but only when warmed up. This bike is a bugger to start. Cough, spit, sputter, clang, etc.

    The valve clearance is perfect, new points/condenser installed, dynamic timing is spot on. Carbs rebuilt (chokes are not reversed) and synced.

    Carb history is as follows... much to my surprise I bought the bike with different model Bings. The right carb is 94/40/114 (for the RS), the left is 94/40/107 (for the S/RT). Even though the bodies are different I followed the Bing catolog and made certain that the jetting of the two carbs are identical for my model year. This means that I replaced all new jets of the same size for both, even though the bodies are numbered differently. Yet the bike still has starting gremlins. Again... once it's warm it runs well.

    I'm assuming that the carb bodies are the same, simply jetted differently for different model bikes. Perhaps this is NOT the case.

    I'm trying desperately to track down my starting issues. Perhaps the forum could suggest a fix. Thanks.
    #1
  2. disston

    disston ShadeTreeExpert

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    I agree with your assumption that the carbs are now matched with all new matched jets, etc. I don't know this for a fact though. We will assume the jet needles are properly installed and diaphragms are in good condition. There are no vacuum leaks at the head/carb interface. You sound like you are experienced.

    Because it is a starting only issue I think the enrichner/chokes are suspect. A couple of common problems, flimsy gaskets that don't hold and get blown out or sucked in. Screws that don't hold, I Locktight these four screws. The Locktightened screws also hold the gaskets better.

    Since we are sure that the enrichner/chokes are on the right side, are you aware the round disk can be installed backwards or upside down? The round disk has an L or an R stamped on the inside so they indicate which carb they go to. But there is also a dot or dimple stamped on the outer end of the rotating shaft that tells if the disk is installed correctly. This dot is off center a slight amount and it needs to be closer to the lever. There is a picture on Snowbum's pages that shows this clearly,

    http://bmwmotorcycletech.info/bingcv.htm

    Towards the bottom of that page.

    The extra gas that the enrichners use is taken from the small reservoir in the corner of the float bowl. There is a small jet in the bottom of this corner of the float bowl. The jet needs to be open (they often get clogged). There is a thin brass tube hanging into the small reservoir that has to pick up the gas. This brass tube needs to be open and not cracked.
    #2
  3. 190e

    190e Long timer

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    Even if your enrichers are correctly assembled and adjusted, some early carbs had only one fuel hole in the disc where as later ones had 4 of increasing size to provide progressive enrichment. The enrichers with only one hole can be anything but progressive and on mine at least seem to provide full on enrichment or nothing which at the very least means you need to know what technique is going to work for a first time start. Don't know if this applies to your bike but the 78/79 R65's have only the one hole.
    #3
  4. headtube

    headtube 6 mesas de invierno!

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    Thanks for your assessment. I'm pretty sure the enrichers are correctly assembled and functioning as they should. The dimple is where it should be on both carbs. However, I did not replace the gaskets during my rebuild. Perhaps I'll do that. For certain, the jets on the float bowls are also clear and unrestricted. Also, no air leaks are present on exhaust or intake.

    Really scratching my head on this one. :becca
    #4
  5. disston

    disston ShadeTreeExpert

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    The gaskets are a big issue. It provides income for one company at least that manufactures a special thicker gasket for our carbs. I have these on my bike but have not had the carbs off since I put them on last year. So they are still in testing, for me at least.

    [​IMG]

    http://realgaskets.com/files/motorcycle.htm

    These are nice but not really needed to fix any problem. They do seem to last longer. I have had the OEM gaskets blown out and the enrichners sucking air because of it. Also use Blue Locktight on the screws. Several other riders report they use a thin coating of a Silicone Sealant on the enrichner gasket. I'm not against that but have found, I think, that the thicker gaskets work well enough.

    When I ordered these I didn't want anything else they had really but it didn't make sense to make such a small order. I ended up with the Silicone valve cover gaskets which I can now say I don't like. I'm still using them tho because I paid for them.

    I have also inspected the surfaces of the disk and the body of the enrichner cover to make sure they are flat. I have heard of the disk and other surfaces being not flat and requiring lapping to make work properly.

    There is an O-ring, you know, in the enrichner? And the brass pick-up tube is open?

    Finally, I think there is an issue that we older riders may be over looking. I, we, are used to working with carbureted engines but many of todays riders have grown up on fuel injected engines. I will suggest the way that I start my bike. If the engine is cold and the temp is below 50* I use full enrichner/choke on start. I also open the throttle by hand a bit, about 1/4 turn, sometimes more. (this you will have to play with) But the idea is different than a FI engine that doesn't get any throttle to start. I then throttle to about 2500 rpm and turn the choke down half way almost immediately. I have the choke off completely in a minute or less in the Spring. In the Winter it takes longer. If the temp is higher I can use less enrichner/choke but I am using more than others think they need.

    Something I learned from another rider in Japan many years ago. He said that his Japanese mechanic there insisted on immediate starting in a well tuned machine. For some reason I have taken this idea to heart and I insist that my bike always starts immediately on the first crank and with very little cranking at that. I never want to be grinding away at the starter and running down the battery. It is just the way it is supposed to be and I insist that it is that way. All this Winter my bike started on the first crank even when the temp was below freezing.
    #5
  6. Plaka

    Plaka Brevis illi vita est

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    I also got the Realgasket silicone valve cover gaskets. They were good for not leaking but they cut. So I replaced them with stock. The oil pan gaskets lasted but using two (oil pan extender) resulted in a too soft stack and excessive squeeze out at torque. I wouldn't even consider them on the choke valve. Gasket thickness matters there. I glue those well and take them apart very rarely. I suspect carb bowls might be a very good application however. Waiting for my cork ones to wear out and I'll try the silicone.
    #6
  7. disston

    disston ShadeTreeExpert

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    Most of the products sold by Real Gaskets are Silicone gaskets that are soft and squishy. I guess some riders like them. I didn't care for the valve cover gaskets but I was considering the oil pan gaskets. Thanks for that insight Plaka.

    The enrichner gaskets are not a Silicone item. It is a thicker paper, or looks like paper.
    #7
  8. supershaft

    supershaft because I can

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    Disston: Those gaskets are paper? If so, I could see those helping. IMO, IF you replace the stock gaskets every time you take the enricher body off, they work perfectly so I really don't have a need for them. Silicon valve cover gaskets, silicon float bowl gaskets, and silicon sump gaskets? I have never needed them. My stock gaskets don't leak. Never have in the 30+ years I have been riding my own airheads. I have worked on numerous bikes that had those silicon gaskets on them and they were leaking big time but I hear tell they do sometimes work. I have never seen it except maybe in passing but . . . .

    Bings shouldn't have stating problems. The only problem I have seen them have is when the choke cable doesn't pull the lever all the way to it's stop. Well, besides more obvious and still fixable issues.
    #8
  9. Plaka

    Plaka Brevis illi vita est

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    Ah so.

    If you want some oil pan gaskets, I got 2. I just made new ones out of siliconed paper. I imagine they would be fine as a single. Doubled felt weird (but worked fine).
    #9
  10. disston

    disston ShadeTreeExpert

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    Sort of a rubbery type of paper I think. But more paper than anything else. A nice product, really.

    I only bought the valve cover gaskets because I wanted to fill out my order.
    #10
  11. rufusswan

    rufusswan Been here awhile

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    You can have everything right, but if the coke cable does not push the choke closed, all is knaught.
    #11
  12. Plaka

    Plaka Brevis illi vita est

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    A good reason for getting rid of the choke cables. A bunch of mechanism goes away with them, they work 100% both ways, never need adjusting and the carb. major servicing (including replacing diaphrams on the road) gets simpler. The stock setup is sort of a goofy creeping featurism thing. First it's one lever on the side of the engine with a rack and pinion getup working push/pull cables with adjusters on the carbs, then the single lever gets moved to the handlebar with a splitter for a total of three cables and I believe a pair of springs. Try moving it to a trash can and get simpler, surer operation. It's a pretty simple mod and people even sell the setup.
    #12
  13. boxerboy81

    boxerboy81 Stay Horizontal

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    Are the float bowl gaskets in good condition? If not, that can contribute to poor cold starts via a leaning of the start-up mixture.
    #13
  14. headtube

    headtube 6 mesas de invierno!

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    Brand new float bowl gaskets. I have gone through these carbs very thoroughly. Perhaps they will come off again to re-inspect the enrichers and purchase new gaskets.
    #14
  15. disston

    disston ShadeTreeExpert

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    Ain't it a drag. Sometimes you gotta take something apart to fix it. :freaky Life is just not fair.
    #15
  16. Plaka

    Plaka Brevis illi vita est

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    How does that work?

    The bowls are fully vented to the atmosphere. As long as the gaskets are present (which sets the bowl height)....
    #16
  17. Lee 303

    Lee 303 razryadka

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    Inspected and repaired as neccesary the carbs on a newly acquired 84 r80rt. Cold stalling problem resolved after I cleaned the dirt and saponified grease out the choke lever detents on the left handlebar control. Now the full setting stays locked. Whereas before you had to hold it with your thumb or it would automaticly creep back to half way and stall out. Now it'll fire right up and stays running (given enough thottle). I no doubt saved all kinds of wear and tear on the switches and relay contacts and starting motor,along with a fair amount foul language.
    #17
  18. boxerboy81

    boxerboy81 Stay Horizontal

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    If the gaskets aren't good, they can allow too much air to enter the circuit during start up and then you have difficult cold starting. Trying new gaskets and ensuring the jet in the corner of the bowl is clear might be an easy fix.
    [​IMG]
    #18
  19. Airhead Wrangler

    Airhead Wrangler Adios Mexico

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    There's a loctite product that I've used on the choke cover in place of a gasket that works great. It doesn't have the tendency to get sucked in like that tiny gasket likes to do. I can't remember the specific product, but it was transparent red and called "anaerobic gasket maker" or something like that. Maybe this stuff? http://www.amazon.com/Loctite-38655-Gasket-Flange-Sealant/dp/B0002KKTTA
    #19
  20. Plaka

    Plaka Brevis illi vita est

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    jet has to be clear. Air is a non issue so long as there is plenty. If the bowl vent is clear, there is plenty. You want the air pressure in the bowl to be at almospheric at all times. Fuel flow is controlled from the bowl, not air.
    #20