Mystery in exhaust ports - Cylinder head

[kiwiz]

In the process of lapping in the exhaust valves on the head of my Z1000J I have noticed that each port has a small cast tunnel which starts near the exhaust guide and runs vertically up to be blanked off by the cam cover. These tunnels do not seem to be joined and do not seem to serve any purpose on my machine at least. Has anyone got any idea of their function?

[Iain marshall]

the ports your on about are part of an emission control system fitted for some markets,basically if fitted the cam cover has reed valves fitted which allow air to be drawn from the air box through a control valve under certain conditions to allow the gasses in the exhaust to continue burning and reduce emissions,you can see reed valve type in the bottom diagram,i fitted a standard cam cover on my GPZ and removed control valve etc,hope this helps

[kiwiz]

As I don't have any reed valves on my 1000J I won't worry about it then. Thanks for the advice