I suspect if there might be anything I might be good at these days, it`s adding to the confusion...(-: I have never had a Facet pump to bits.
My mid 80`s +8 has a very similar Facet type fuel pump and I have had experience of the SU pumps over a number of years... I suspect the operation of the pumping mechanism is dependant on the pressure sensed in the fuel supply line from the pump to the carbs, which when pressure is sensed in that part of the line, holds the electrical contact points in the switching mechanism open, thus the pumping action stops, until the pressure in the fuel line drops to the degree that the switching points close, thus activating another stroke of the pump to build pressure. Each stroke of the pumping action being heard via the audible click..?
When the ign is first turned on and perhaps dependant on how long the car has been standing unused, the fuel in the carb(s) may have evaporated to some degree and thus the float needles will have opened up as the level in the float bowl seems likely to have dropped... That perhaps being the case the pressure in the fuel line will deplete as some fuel will then find it`s way into the float bowl of the carb(s)..?
When the ignition is turned on, the fuel pump will sense the lack of pressure in the fuel supply line and thus tick rapidly in order to provide the appropriate pressure/ fuel supply, to the carb(s), up to the point that the pressure is restored to the required pressure set point when the ticking will stop..?
In a situation where the ticking does not slow down and stop, there is just a chance that there could be dirt in the float bowl needle valve inhibiting it`s closure. Such a situation is not unlikely if there is some sort of contamination in the fuel picked up from the tank..? In line filters can assist in keeping the needle valves from fouling.
If the needle valve(s) might not be seating correctly and thus allowing fuel to seep past them into the float bowl, the pressure in the line will drop at whatever rate the needle valves allow the fuel to seep past.
In such a situation the float bowl has an overflow pipe that allows the excess fuel in the float bowl to drain of below the car, in order that the excess fuel does not flow through the carb(s) and into the engine, with all the negative possibilities that situation could create in time..?
Therefore, leaky needle valves could cause a reduction in the fuel line to hold pressure. On the other hand the seals in mechanical stage of the pumping mechanism might it`s self suffer a degree of wear in time, which could cause the line pressure to leak back past the pump and back into the tank to some degree and thus cause an occasional tick...?
Just to add fuel to the fire of possible concern...no pun intended...(-: There is a chance that modern bio fuel types ( E10) may in time affect not only the pump internals, but also any rubber in fuel lines, which may also exacerbate needle valve crud pick up, as the fuel lines degrade internally..
Just treat the tick like a heart beat... and if it ticks too fast for too long, THEN there may be good reason to get in amongst things...?
More than happy to be proved to be entirely wrong...again..(-:
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