Weber air bypass screws!

[Neil Bardsley]

I was trying to balance my 40 idf weber carbs at idle on Saturday. They are equal left to right. 1 and 4 are almost equally the same. Just under 4 on my air flow meter while 2 and 3 are just a fraction higher. There isn't much in it but then I had the idea of opening the air bypass screws on 1 and 4 to rise the air flow a little. However, I cracked out the nut but it didn't change the flow. Now looking at the diagram again I think I need to loosen the nuts then screw out the bypas screw (which I didn't do) and retighten the nut? Works a bit like when adjust the valves?

[Jim Karaba]

Yes the nut is just a locking nut to maintain the bypass adjustment

[Neil Bardsley]

Yes the nut is just a locking nut to maintain the bypass adjustment

thank you

[John Brooks]

Out = up. In = down on the unisync

[Neil Bardsley]

Thanks I did this on my 912, which also has 40 webers, and got the front back cylinders in sync. Once they were you could hear the engine rev smoother and faster. I checked the valves before and I think they are good. Could incorrectly set valves impact the flow?

[Jim Karaba]

yes