Why on an old tractor is there a pipe running from the fuel filter back into the sump?
it sounds like someone has rerouted the fuel return pipe which should run from the filter back to the tank to allow excess fuel to drain back to the tank when engine is over running i.e when throttle is released for gearchange,etc. I would re route this line as petrol is a cleanser and as such, mixing with the oil it will clean off the lubrication from essential components leading to failure or siezure.
