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The over heating was on the left side.
Well I just ran the bike with my manometer hooked up. All the vacuum pull is on the right side at idle and partial throttle.
Regardless of what I do with the throttle stop screws I can't effect the out-of-balance much.
Throttle cables have a little play and are very close to equal.
Before bringing the bike in I did a compression test - right on the money and the same on both sides.
I hate mysteries!

Are the needles equally set? Are the diaphragms both ok? There...did that help? Choke closed off?

Where the hell's GSPD?

GSPD YOU ARE MISSED!!!

I'm too scared to offer advice, I send people on wild goose chases!

Sounds exactly like a plugged or restricted idle circut to me. During the rebuild something could have found its way into one of the passages? Don't forget there is one on each side of the butterfly.

I have a question for GSPD too.

R90Steve wrote: Don't forget there is one on each side of the butterfly.

Steve - Can you explain that a little more to me please?

Great diagram, but I still don't understand about the air passages.

dougie wrote:Great diagram, but I still don't understand about the air passages.

I don't have a carb in front of me, but there are a couple of air passages that start to the bottom right of the diagram. One goes to the main jet area and pre-mixes the main jet fuel with air, forming an emulsion, which then is regulated by the needlejet and the jetneedle.

The other smaller passage goes to the idle jet and mixes air just above the idle jet in the area where the jet is crossed drilled. This then passes the mixture screw into the ventiuri. The idle air passages are tiny and easliy blocked by bitts of old Oring, dirt of grease.

There is a good pic of the idle circut here: http://www.omnilex.com/public/bmw78/cvcarb.pdf

Garnet wrote:

dougie wrote:Great diagram, but I still don't understand about the air passages.

The other smaller passage goes to the idle jet and mixes air just above the idle jet in the area where the jet is crossed drilled. This then passes the mixture screw into the ventiuri. The idle air passages are tiny and easliy blocked by bitts of old Oring, dirt of grease.

Looking at one of my carbs -
on the air intake venturi at 6 o'clock their is a passage that goes straight to the needle area.
Beside that is a smaller brass hole. Is that the air feed to the idle jet?
How do you check the very small openings at the butterfly? (All I have been able to do is carb cleaner and compressed air.)