74 85HP 850 fuel replaced..still no fuel

[Biggskye]

74 85HP Merc only runs while you pump primer bulb. Have replaced fuel pump diaphram and check valves. Maybe problem with crankcase compression? Runs great if you keep pumping primer bulb

 

[Chris1956]

or air leak between bulb and motor. Or air leak in fuel line connector.

 

[jimmbo]

What about the gasket between, and gasket sealing surfaces on the fuel pump and engine block?

 

[Chris1956]

He likely has one or two of those triangle-shaped fuel pumps. They connect to the crankcase via hoses and brass fittings. Sometimes the hoses leak or collapse. Sometimes springs are used inside the hoses to keep them from collapsing.

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[jimmbo]

I thought the triangle pumps each got their pulses from two transfer passages directly, no hoses except for fuel. One transfer passage for the main chamber with the check valves, the other transfer passage operated a second chamber without check valves that dampened and smoothed the fuel flow

 

[Chris1956]

Actually Jimmbo, I think you are correct. It has been some time since I worked on one of those. I never had any trouble with them...

 

[jimmbo]

There are so many variations, I know I have forgotten an item or two, or three, over the years.:embarassed:.

 

[Vt MercMan]

If the bulb is soft but not collapsed, the pump isn’t drawing fuel. If the bulb or line are collapsing, there is a retrriction in the fuel inlet or a venting problem. Are you sure you got the check valves in correctly? You can check by slightly squeezing the bulb to see with the pump split to see where the fuel enters. That cavity should have the valve to allow inward pressure and the other one would be flipped.
You could help us by either posting a pic or describing the vacuum/pulse arrangement for your pump.