Results 1 to 7 of 7

Thread: Carb question

  1. #1
    Smoooooth at 430 gch71's Avatar
    Join Date
    Dec 2011
    Location
    Katy, Texas
    Posts
    172

    Question Carb question

    Will 40mm carbs fit on a 1975 R75/6???
    Glenn
    ...driving to work on my airhead
    '74 R60/6, '75 R60/6(boxes)

  2. #2
    Administrator 20774's Avatar
    Join Date
    Sep 2005
    Location
    San Antonio, TX
    Posts
    13,075
    I'm thinking that there will be a size issue mating with the intake spigot to the head. Plus, a larger bore in the carb doesn't necessarily mean good things when the engine can't use it. The intake valves are such that it will only take so much air...a bigger carb doesn't really help that.

    Why are you looking at this? As a temporary replacement?
    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!

  3. #3
    James.A
    Guest
    Quote Originally Posted by Gch71 View Post
    Will 40mm carbs fit on a 1975 R75/6???
    I think Kurt is exactly correct on this one. Having said that, you are familiar with the way that Type 53's fit to your 600's, yes?...You would need to do something like that with rubber sleeves or stout fibre board tubes. You would also have to spend a lot of time trying to get the jetting correct and reading spark plug color to determine rich/lean conditions. Not worth it in my estimation.

  4. #4
    Smoooooth at 430 gch71's Avatar
    Join Date
    Dec 2011
    Location
    Katy, Texas
    Posts
    172

    Thank you gentlemen

    Nope nothing wrong, my daily driver (74" R60/6) is doing fine. I am starting on a project with the other bike I found (1975 R60/6) a few months ago, upping it to 750, got the cylinders, heads and cam, just looking to see what I can put on it to breath properly.
    Glenn
    ...driving to work on my airhead
    '74 R60/6, '75 R60/6(boxes)

  5. #5
    Registered User lkchris's Avatar
    Join Date
    Mar 2003
    Location
    Albuquerque, NM
    Posts
    4,785
    A 750 doesn't need 40mm carbs and will not achieve any advantage by fitting them.

    When 40 mm carbs were fitted to R100s, it was in conjunction with larger intake (and exhaust) valves. If similar modifications are not made to a 750 engine, it will continue to "request" the same amount of fuel/air as always. BMW's middle name is "motor" and you can take to the bank the notion that your engine is not "strangled" in stock configuration.
    Kent Christensen
    21482
    '12 R1200RT, '02 R1100S, '84 R80G/S

  6. #6
    James.A
    Guest
    Quote Originally Posted by Gch71 View Post
    Nope nothing wrong, my daily driver (74" R60/6) is doing fine. I am starting on a project with the other bike I found (1975 R60/6) a few months ago, upping it to 750, got the cylinders, heads and cam, just looking to see what I can put on it to breath properly.
    Oh,.... If you have a set of 32mm Bing CV's you should have little trouble getting your hands on correct jets. Or, you might try something deviant like Mikuni's.

  7. #7
    Smoooooth at 430 gch71's Avatar
    Join Date
    Dec 2011
    Location
    Katy, Texas
    Posts
    172

    OOOOO so deviant

    Quote Originally Posted by James.A View Post
    Oh,.... If you have a set of 32mm Bing CV's you should have little trouble getting your hands on correct jets. Or, you might try something deviant like Mikuni's.
    Ok, that sound good....yes the Mikunis were in the back of my head and Im not trying to keep this bike "pure original" thats what I have the other one for. I think Rocky Point still sells them.... My ultimate goal is to BUILD MYSELF a reliable bike with modern touches...yea I know I hear the purists bickering already buts it a project that I need to do to keep my sanity..... I'm in the planning stages only but when I start I'll start posting picks.
    Glenn
    ...driving to work on my airhead
    '74 R60/6, '75 R60/6(boxes)

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •