Best carbs for 77 RS big valve motor?

Discussion in 'Airheads' started by beemerphile, Jul 23, 2013.

  1. beemerphile

    beemerphile Long timer

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    I am doing a ground-up restoration of my 77RS (into an S because I lack the original fairing). It will get Nikasil cylinders and new compatible rings, rods reconditioned, and the heads rebuilt and dual-plugged. It will also get a crank-mounted ignition system on an EnDuraLast alternator. It will retain the stock 308 cam with a new chain (I guess). It will get a new set of Keihin 40mm stainless pipes.

    The question: What is the best carb set-up for this combination? I do not have the stock 40mm Bings. What is has is a dogged out set of Mikuni 38mm flat-slides. What SHOULD it have if it were to be the very best it could be?
    #1
  2. Jon-Lars

    Jon-Lars Jon-Lars

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    Dellortos.

    [​IMG]
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  3. supershaft

    supershaft because I can

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    Dellorto's . . . and a BMW 336.

    I prefer the rubber mounted Dellorto's over BMW's clamp mounted units. I like them without the choke too. One less cable. I just use the pumps versus the choke. My Dell's don't have the enricher bodies on them and they have the pumps disconnected. It would be impossible to start but I have Dell's with ticklers like a /2 Bing.

    One reason I like Dells is because the airbox snorkels fit them. I have late model square airbox snorkels on mine with no radiator hose and double hose clamps like in the photo above. I filed about a third of the velocity stack threads off and the late snorkels fit right on them with one hose clamp and no hose just like they do on the later stock Bing setups. Way cleaner look IMO. That and two cables versus four.
    #3
  4. beemerphile

    beemerphile Long timer

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    Not sure I follow all that. Wouldn't have a picture, would you? I was not aware there were so many options with the Dellorto's. Much to learn here.

    Jon-Lars, your RS is awesome.
    #4
  5. Jon-Lars

    Jon-Lars Jon-Lars

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    I just put them on my 77RS, using the same intake and fittings as on my R90S:

    [​IMG]
    #5
  6. supershaft

    supershaft because I can

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    Look through a Dellorto manual. They have all the options. They are on line.
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  7. Bill Harris

    Bill Harris Confirmed Curmudgeon

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    Ooooh. Nice project. Coming back from the darkside, eh? :D

    From what I've heard, the Dellortos work very well. And just look impressive on the bike. Best of luck finding a good set...

    On the resto, pics please as the work progresses... :deal

    --Bill
    #7
  8. DoktorT

    DoktorT BigBrowedNeandereer

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    Best at what?? If sport touring for long distances and easy maintenance, the stock 40mm Bings will do just fine, thank you. Use the stock Euro jets for that year and you are golden.

    Others can do just fine, if your skill in setting up the right jets is up to the task. If tinkering through such trials and errors is something you like doing, do that.

    But factory Bings is a quicker road to decades of good service with stock cables and procedures giving easy install setup.
    #8
  9. Biebs

    Biebs BMW Airhead

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    Since this is open to everybody's opinion (you asked!!) I would go with fuel injection!!!

    AirHead with fuel injection:freaky that's the Ticket!!

    Ok - 38mm flatside - stick with the flatside carbs.

    Fuel Injection Hmmm???:deal I planted a seed let's see if it will grow.
    #9
  10. beemerphile

    beemerphile Long timer

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    No Bill, I am keeping the darkside and just two-timing it a bit. I bought back a 1977 RS that I bought new and sold to a friend in 1991. It has been melting into his barn floor for the last decade and I thought enough was enough.

    As far as the goals for the build - a strong performing S bike. I don't mind fiddling but I'm not into mechanical masturbation. I'd like something with a starting set-up that would run with some tweaking to optimize it. I don't want to have to "discover" the entire set-up.
    #10
  11. beemerphile

    beemerphile Long timer

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    Links to this? I can find a page full of PHM type carbs on Dellortodirect, but nothing that explains what the differences are between the different models (such as BS/BD, CS/CD, NS/ND, etc.). Is there a US reseller that has the knowledge to kit one with starting jetting, cables, and connectors as a Sudco or Rocky Point would do with Mikunis and Keihins?
    #11
  12. Bill Harris

    Bill Harris Confirmed Curmudgeon

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    Ah, then this IS going to be a good project to follow. A resto of an old bike is one thing, but one with your history attached is entirely on another plane.

    --Bill
    #12
  13. mnsty

    mnsty Been here awhile

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    Bings
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  14. beemerphile

    beemerphile Long timer

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    I met my wife of 31 years on this bike. I had it running for a few moments before I began the teardown. When my wife heard it she said it was a flood of memories. It was my first BMW and cost me $4,755 back when a rather nice car did not cost that much. So, history, yes.
    #14
  15. rheritage

    rheritage Been here awhile

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    I have a 78 Euro 100RS with stock 40mm Bings, plan is to install Mikunis, already have them on my R75/5 and love'em.
    #15
  16. Rucksta

    Rucksta SS Blowhard

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    I have a project to remove the Dels and reinstall Bings.
    (to stop cable chafe when using the 43 lt Acrebis tank)

    The project has been sitting on Ray Peaks bench for near two years.
    Neither of us are motivated.

    Has anyone ever gone back to Bings?
    I don't seem to be able to find their posts telling us how excited they were with the change.
    #16
  17. beemerphile

    beemerphile Long timer

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    Maybe that's telling...

    - If the tops of my boots were too dry and odorless, I'd install 40mm Bings
    - If I needed a constant bruise on my right mid-shin, I'd install 40mm Bings
    - If I wanted to turn the gas off by kicking it, I'd install 40mm Bings
    - If I wanted to twist - wait- go, I'd install 40mm Bings
    - If I didn't like to use engine braking, I'd install 40mm Bings

    I'm sure there are other reasons I can't pull up right now. To the benefit that they are undemanding, I would say "So is an ugly girl". The Bings are really the only thing I have ruled out. I have Mikunis on my R75/6 and they do well, but I wanted to take this build upscale from the R75 where it makes sense. Just trying to learn what is out there and what kind of trials or sucesses people are having. No bones to pick with the Bingers. I spent a few decades there.

    Fuel injection! Hmmm? How to get a fuel pump into a /7 tank???
    #17
  18. Sniper X

    Sniper X De Oppresso Liber

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    I had 38mm mikunis on my 77 R100Rs and would never own another Airhead without putting them on it as well.
    #18
  19. beemerphile

    beemerphile Long timer

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    Flat or round slide?
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  20. supershaft

    supershaft because I can

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    The explanation is somewhere in the manual. I can't remember where without going through it.

    The choice pretty much boils down to Mikuni's or Dell's. Flat slides or round? The flat slide Mikuni's come with independent float floats just like Bing use to sell in their 'alcohol proof' floats. In both brand carbs that float system is very problematic. Very prone to constant flooding. Both type Mikuni's take some engineering to get them back to the airbox. The best way to do that IMO isn't that great of a setup. Plus it looks like crap. And you have to come up with cables. The airbox setup with Dell's is great. R90S cables. R90S jetting will get you started. Just lean it out from there. Performance? I would rate all three too close to tell keeping in mind that any 38mm Dell or Mikuni has way more low end and top end and everything in between than a 40 OR 32mm Bing.
    #20