That is a decel valve. You can see the fuel supply from the right engine shelf running to the fuel rales. Visible also is the >30 year old plastic return fuel line. The decel valve uses 13mm vacum lines from the breather to the plenum with a 5mm vacum line to the plenum. To decel or not to decel is a much less important question than to replace fuel lines or not to replace. Forgive me, I was reading Shakespear with my son last night.
