I have used a local place (to me) several times. R D Cox are based in Reading and they will blast and 2 pack your frame and bake it to a really hard finish.They've always done a great job for me and other local restorers use him inc Allen Milyard. Not very local to you guys but it is an option.

Is the valve timing correct?

Here are mine also from Early 75 Z1B

That's what I've got on mine and they work well.

Lovely bikes, well done on the A4

Get hold of the parts book, this will help you to see the correct assembly of the bike. You can find it in various online places but CMSL has all the diagrams

I've seen rims like that on a CB750

Something you could try to see if it runs any better is to connect the vacuum take offs. Connect 1 to 4 and 2 to 3 with some 5mm fuel pipe or similar . This will mask differences between the carbs and may help running. Good luck with the bike and don't give up, you will crack it.

I would think this is still a carb issue. Have you tried another set of proven carbs since the rebuild?

Glad you got the offending article out of the engine. Don't ask me how I discovered the air line solution !!

Stick an air line down the chain tunnel and blow it out of it's hiding place ( if it's in there ! ). Good luck.

I have used IMD for a rebore and piston kit for my A4. Excellent service and quick turnaround.

Congratulations Philippe, that's absolutely fantastic.

Lovely job, well done

Here's how it looks after 4 years......