These are the upper components of the Thermal Vacuum Valve (TVV). It is positioned next to the yellow arrow which points to the cooling system bleed screw in the second picture. You access the valve by simply unscrewing the valve cap.
As posted by Dom, this valve is open to atmosphere while the engine is cold. It stops the vacuum feed to the vacuum advance diaphragm on the distributor so that the engine timing remains retarded. It also affects the operation of the EGR valve until the engine is warm.
Once the engine coolant reaches a pre-determined temperature, the valve closes and the vacuum advance is allowed to operate normally.
I found that the components were caked in fine dust, which is sucked into the valve.
I will endeavour to work out a way of stopping water and mud from sitting in the valve intake. I also want to filter the air which is sucked into it. I think raising the intake via a hose to a cheap fuel filter next to the diff breathers will be an easy solution.
You may have noticed that my TVV has a hose clamp around the base. It there because I accidently snapped off the bottom hose barb while bleeding the air from the cooling system. The hose clamp holds a 3/16 15mm long pop rivet on as a replacement.
The hose clamp has a hole drilled through it to hold the rivet and I used silicon to seal the rivet to the valve body, (I was very careful not to get any silicon into the valve).
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