Onan 7.5 MDJE problem

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Onan 7.5 MDJE problem

Postby Berger » Mon Oct 28, 2019 12:14 pm

Hi All I have a 1977 Onan 7.5 MDJE that was running rough. I replaced the primary and secondary fuel filters as well as the cleaning out the catch bowl at the fuel transfer pump, the fuel had evidence of water in it. Everything back together I can't seam to manually pump the transfer pump. There is a lever to manually prime the system but it's dead, zero resistance. Is it supposed to have zero resistance? What am I missing?
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Re: Onan 7.5 MDJE problem

Postby gsanchez » Fri Nov 01, 2019 1:26 pm

Could be the diaphragm in the lift pump is broken. it is easy enough to dismount and take apart the pump to inspect.

You might first try to rotate the crankshaft a bit, either manually or with the starter, as in some positions the manual pump lever does not work.
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