NB: These instructions are given for guidance only and cannot engage the author's liability in the event of misinterpretation, failure to assess the vehicle's actual condition and/or non-conformity, unsuitable mechanical practice or the use of inappropriate tools.
Dell'Orto PHF accelerator pumps. New pump diaphragms should only be fitted if all the carburettor seals are being replaced too. The job is straightforward provided the sealing faces are clean and sound — but it is important to re-prime the pumps.
Re-priming
- Remove the plugs of the pump circuit.
- It is sometimes possible to prime by gravity, filling the circuit from the top, but the best way is to draw fuel up from the float bowl to the port, using a syringe with a sealing tip on top of the carburettor body. Once the circuit is full, refit the plug with its new seal and test by working the throttle lever several times.
- Dell'Orto documentation gives a delivery of 4 cm³ per 20 pump strokes, but in practice this figure is imprecise: above all make sure the fuel jets are clean and reasonably equal across the three carburettors.
- If fuel still does not squirt from the pump jets, check that the non-return valve is not stuck.