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Thread: Dellorto carbs on a R100

  1. #1
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    Dellorto carbs on a R100

    Consensus on Dellorto carbs on a '81 R100. Good bad or indifferent? Looking at a bike that has them. I can kinda work my way around Bings but I've no experience with the Dellorto.

  2. #2
    Liaison 20774's Avatar
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    What are you after? Do the Bings not work right or do you want some other kind of performance? As you know, they were only on one model of Airheads, the R90S...I guess to make it more "go fast". Personally, the Bings do a pretty good job of ironing out things, offer a small actuation, do some little adjustment when changing altitudes out west, etc.

    Snowbum has a page on the Dells...probably more about how they operate, though:

    https://bmwmotorcycletech.info/dell.htm
    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!

  3. #3
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    I've had/have Airheads and always been happy with the Bings. The Dellortos just happen to be on the RS I'm going to look at. I'm more interested in ease of maintenance and reliability, and if they change the value of a used Airhead one way or another. Thanks for the reply.

  4. #4
    Liaison 20774's Avatar
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    I don't think they add or subtract value one way or the other. Seems to me it's just a personal preference to have the Dells. Given that they have accelerator pumps (IIRC) then you get more oomph when you twist the throttle. I suppose once set up, and treated like any other carb, they should be fine. I've never been inside a Dell Orto so don't know how much more complicated they are. You certainly have good experience with the simplicity of the Bings.
    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!

  5. #5
    Registered User lkchris's Avatar
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    The main difference with the Dellortos is that they have an accelerator pump. This means you could feel different response when demanding acceleration. There is really no hesitation with Bings.

    Don’t buy any hype that your motor is strangled by too-small carbs. BMW does it right. With the same cam timing, lift, and valve sizes, your motor continues to “ask” for the same thing. A larger carb does not create forced induction.

    In years following the R90S, BMW created some “hot rod” Airheads for the Paris-Dakar rally. They used Bings.
    Kent Christensen
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  6. #6
    My R100 was the best of my airheads and I had no problems with the Bings. If you're looking at a bike with Dellortos and can get it for the same price as with Bings consider seeing how they work and swapping for Bings later. You may be able to sell the Dellortos for more than a set of Bings would cost.
    '61 Clubman's Gold Star, '13 690 Duke, '13 Daytona 675R, '18 Street Triple RS, 2020 R1250R (gone but not forgotten: '76 R75/6, '84 R100, '76 R90S)

  7. #7
    Registered User STEVENRANKIN's Avatar
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    Slightly quicker

    A bike with Dellorto carbs set up properly will be a bit quicker in acceleration, when the throttle is cranked open due to accelerator pumps.

    They are a little more expensive price wise than bings, hence BMW took them off of bikes after using them for the R90S series.

    I have thought often about purchasing a set for both of my bikes.

    The only reasons I don't are because my R100RS has 40mm carbs, not 38mm. And the R80RT have 32mm carbs not 38. Good used Dellorto carbs are abundant in 38mm.
    Plus, I don't know about cables for the bikes to hook them up.

    I do have a line on a set of 40mm Dellortos, they may find their way on my RS this winter. St.

  8. #8
    Some guys, back in the day, bought into the go-fast aura of the R90S “superbikes” hook, line, and sinker. Del’Ortos on an R100 are mostly that—if they had been a really great improvement, presumably BMW would’ve used them for more than three years.

  9. #9
    Dellorto carbs on an R100 are a sure sign of tinkering. Now, often tinkering on an Airhead is a good thing, but also often when done not quite right tinkering by former owners can be a nightmare. To me they simply indicate I would need to carefully inspect for other things which might have been done - correctly and/or not so correctly.
    Paul Glaves - "Big Bend", Texas U.S.A
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    http://web.bigbend.net/~glaves/

  10. #10
    Registered User barryg's Avatar
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    From reading the BMW motorcycle history books, it appears with the coming of the performance oriented R90S, Bing did'nt have a carb available big enough to do the job. So BMW used what was available, which was the Dellortos. Bing developed the larger 40mm carb for coming of the performance oriented R100S, RS, RT in late '76 for the '77 model year.

  11. #11
    JohnWC
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    It's been a few years back, but I think my 1976 R60/7 had Dellorto carbs on it. As I recall, it was a very quick accelerating bike. Of course it had a low geared final drive that helped also. In the years I had the bike, I never had any problems with the carburetors. Or anything else on it for that matter.

  12. #12
    The main difference between the Dellortos and the Bings is that the former is a slide carburetor and the latter a diaphragm actuated carburetor. With a slide carb, when you twist the grip,you move the slide which directly controls the air flow into the carb. With a diaphragm carb, you do not have that direct connection. When you twist the grip, you move the carb butterfly which sets up a pressure differential which acts on the diaphragm which eventually lifts the slide which controls air flow into the carb.

  13. #13
    Quote Originally Posted by swall View Post
    The main difference between the Dellortos and the Bings is that the former is a slide carburetor and the latter a diaphragm actuated carburetor. With a slide carb, when you twist the grip,you move the slide which directly controls the air flow into the carb. With a diaphragm carb, you do not have that direct connection. When you twist the grip, you move the carb butterfly which sets up a pressure differential which acts on the diaphragm which eventually lifts the slide which controls air flow into the carb.
    And in either configuration carburetors are crude instruments at best - 19th century technology for the 21st century. Which is why they provide poorer fuel mileage and higher emissions that modern fuel injection systems.
    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://web.bigbend.net/~glaves/

  14. #14
    Quote Originally Posted by jconway607 View Post
    It's been a few years back, but I think my 1976 R60/7 had Dellorto carbs on it. As I recall, it was a very quick accelerating bike. Of course it had a low geared final drive that helped also. In the years I had the bike, I never had any problems with the carburetors. Or anything else on it for that matter.
    Your R60/7 had Bing slide throat carbs as OEM equipment, rather than Dell'Ortos.

  15. #15
    Quote Originally Posted by 2slowwheels View Post
    Consensus on Dellorto carbs on a '81 R100. Good bad or indifferent? Looking at a bike that has them. I can kinda work my way around Bings but I've no experience with the Dellorto.
    If you do buy the bike, I have a freshly rebuilt pair of 40mm Bings I'd be interested in trading, assuming the ones on the bike are PHM38's

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