Carb question

[gch71]

Will 40mm carbs fit on a 1975 R75/6???

[20774]

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?

[James.A]

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.

[gch71]

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.

[lkchris]

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.

[James.A]

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.

[gch71]

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.