Boxerworks.com

The 1970 carbs were 01 & 02 as I remember. At about the time that the 71 came out (maybe exactly) the 03 & 04 carbs came out. The 1970 carbs were impossible to tune properly. A few years later BMW came out with a fix and it mostly solved the adjustment issues.

The slide needed to be raised up in the body a bit more. To get this done, a small hole was drilled in, tapped and a small screw installed with locktite. The screw head held the slide up just enough to make a big difference.

I only mention this because somewhere out there may be another set of very hard to adjust carbs that need this modification.

Does someone have the update from BMW? I think that the screw was a 4-40.

Duane, are those early carbs the only ones without a vacuum screw too?

Duane Ausherman wrote:The 1970 carbs were 01 & 02 as I remember. At about the time that the 71 came out (maybe exactly) the 03 & 04 carbs came out. The 1970 carbs were impossible to tune properly. A few years later BMW came out with a fix and it mostly solved the adjustment issues.

The slide needed to be raised up in the body a bit more. To get this done, a small hole was drilled in, tapped and a small screw installed with locktite. The screw head held the slide up just enough to make a big difference.

I only mention this because somewhere out there may be another set of very hard to adjust carbs that need this modification.

Does someone have the update from BMW? I think that the screw was a 4-40.

Snowbum has the info...

http://bmwmotorcycletech.info/earlybingR75CV.htm

I'm surprised he recommends spraying brake cleaner to check for leaks. Brake cleaner that gets vaporized by heat can produce a very toxic poison gas and should be avoided!

Tim Shepherd wrote:Duane, are those early carbs the only ones without a vacuum screw too?

Yes, the vacuum ports came out on the 09 & 10 carbs in 72............ as I remember. We were so excited to "finally" have the ability to use real tools to adjust carbs. Wrong, it is faster and better to tune by ear for someone that does them often.

Tim Shepherd wrote:I'm surprised he recommends spraying brake cleaner to check for leaks. Brake cleaner that gets vaporized by heat can produce a very toxic poison gas and should be avoided!

I use an unlit propane torch.

the quinner wrote:
I use an unlit propane torch.

Also helpfull for finding spark leaks.

Duane Ausherman wrote:

Tim Shepherd wrote:Duane, are those early carbs the only ones without a vacuum screw too?

Yes, the vacuum ports came out on the 09 & 10 carbs in 72............ as I remember.

I have one pair of 9/10s with vacuum ports and one set without. Both on 72 engines, what they started life is unkownn.

Garnet wrote:

Duane Ausherman wrote:

Tim Shepherd wrote:Duane, are those early carbs the only ones without a vacuum screw too?

Yes, the vacuum ports came out on the 09 & 10 carbs in 72............ as I remember.

I have one pair of 9/10s with vacuum ports and one set without. Both on 72 engines, what they started life is unkownn.

That is quite interesting, but just because they advertised it, doesn't mean that it happened at exactly the same moment of the new models. I have seen this happen so many times over the years that I just had to add that caveat.

I have also seen them send out a few bikes with some old parts. I guess that they found a box stashed in some corner and just put them back on the assembly line to get used up. Or, maybe the parts department now had the new parts in stock and didn't want to ship out the older version, so they sent it to the production line. They still got shipped out, but by a different department. We may never know.