[TasRat]

In addition to the coolant from via the gasket at the base of the carby another possible cause or atleast it might contribute is a sticky ERG valve (the vacuum controled Exhaust Recirculation System) under the carb on the manifold.

I blocked mine with a shim.

This may explain why it ran crook with the new carby and changed after driven hard.

I also cleaned the PCV, hoses and iside of rocker cover which were blocked with shit,