by Skywatcher » Thu Dec 07, 2023 2:49 pm
Hi BLES
If the engine runs fine on a gravity feed temporary fuel supply, you'll have maximum vacuum pulse at idle. If the pump is not delivering at least 4 oz per minute into a clean container at idle, this would suggest a fuel restriction problem further up-stream. Disconnect the inlet line from the pump and remove the fuel cap then blow the line back with 5 to 10 psi regulated air. If you don't hear bubbling in the fuel tank, you've got a plugged filter, a plugged line, broken or disconnected pick-up tube in the tank or a fuel valve turned off.
When you have the engine idling on a gravity feed fuel supply, disconnect the pulse hose from the fuel pump, the engine should start running rough or missing on one cylinder. If there's no change in the engine, you have a plugged vacuum pulse line. These pumps work on vacuum only, the vacuum pulses compress the spring under the diaphragm. The built in spring pushing back against the diaphragm is what gives you the actual fuel pressure. Hope this gives you a few ideas. All the best,
Sky
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