07-08-2019, 04:19 PM
(This post was last modified: 07-08-2019, 04:21 PM by David Stepney.)
There has been a comprehensive thread on this earlier. A search on this website should reveal this The replacement pumps are based on the later (and larger capacity) 'U' type pump rather than the earlier 'T' type pump originally fitted to the Seven.
The pump works by the lever running on the camshaft pulling the diaphragm down, sucking fuel from the tank, whilst the return stroke is governed by a spring in the bottom of the pump which sends the fuel to the carburettor.
On the replacement 'U' type pumps, the return spring is considerably stronger than the original 'T' type. An effective cure is to replace the return spring in the replacement pump with that from a 'T' type pump. Fitting a thicker gasket/spacer between the pump and the crankcase will reduce the capacity of the pump but will not affect the delivery pressure, and thus may not be a very effective cure.
Hope this helps.
The pump works by the lever running on the camshaft pulling the diaphragm down, sucking fuel from the tank, whilst the return stroke is governed by a spring in the bottom of the pump which sends the fuel to the carburettor.
On the replacement 'U' type pumps, the return spring is considerably stronger than the original 'T' type. An effective cure is to replace the return spring in the replacement pump with that from a 'T' type pump. Fitting a thicker gasket/spacer between the pump and the crankcase will reduce the capacity of the pump but will not affect the delivery pressure, and thus may not be a very effective cure.
Hope this helps.