As the others have stated take the cover off the front where the suction screen is located and check the plastic key in the drive gear. If the pump is left on too long in by-pass without pumping it will shear the key as a safety precaution. E in the attached schematic. Also check the O-ring on the by-pass poppet. I had a torn o-ring on a GPI pump this summer. It would not pump just like yours. Luckily I had a clear filter bowl on it and saw the piece of O-ring in the bottom. My O-ring was original though and was at least 20 years old. C in the attached schematic and accessible through the top pipe plug.
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 P7270002 (Medium).JPG (72KB - 591 downloads)
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GPI 12 volt fuel pump wont pump-almost new
