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The most likley cause is a torn diaphram in the vacum govenor. This will cause over fueling. Remove the two pipes that run from the top of the govener up to the manifold (mark the pipes for correct re-instalation). Remove the govenor by removing the 4 bolts and inspect the diaphram. Make a note of how the backing plate is installed before taking the diaphram of the govoner rod. It will probably be split around one of the folds. The diaphram is available from New Holland dealers. The govenor works in the following manner. On start up, the govoner is set to full fuel as there is no vacum. (Thats one of the reasons why Fordsons start so easy) At low throttle aplications, a vacum is formed in the inlet manifold by the cylinders trying to "suck" air past the throttle buterfly. This vacum sucks the diaphram against its spring, this that is conected to the fuel rail in the injector pump, thus reducing the fuel flow. As the trottle opens, the vacume is reduced and the diaphram alows the injector pump to supply mor fuel by opening the fuel rail. When the diaphram splits, the fuel rail does not close off properly and hence the smoke. The excess fuel devive does not overide the fuel rail at partial openings. If this was the cause the smoking would tend to be more eveident a full throttle.
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