Sometimes its fine, Sometimes it is rough with white smoke and lack of power! There are No knocking noises though.

Fuel bowl checked for contaminants and filter replaced (All very clean, no metal particles)

we are at around 180,000 here.

It always fires first turn but when it is misbehaving and cold, it will sometimes stall and need to be restated two or three times.

This is a mechanical pump, Is there anything mechanical that can come "Loose" (for want of a better phrase) internally that can cause these intermittent symptoms? It feels like the timing is sometimes correct and sometimes retarded so I am wondering if there is something loose/worn in the centrifugal governor or similar! (Though there is no easy way of telling)

I am minded to have the pump checked by a diesel rebuilders (I have one nearby fortunately) unless anybody has any alternative suggestions.