Old 3-71 Detroit issues

3-71 Detroit engine will only start when governor is pulled and RPMs climb very slow. Any input would be appreciated, thanks.

Does it operate normally after starting?

It builds RPM very slowing, and when I come in on the winch it bogs down and has no power.

Assuming you have fresh fuel filters installed, the first thing to check is the rack. Make sure no injectors are sticking. If they’re ok, check the fuel flow. If it’s starving, try using the priming pump to see if RPMs pick up. Several possibilities can cause starving. Bad fuel pump, stuck check valve, fouled or defective fuel shut-off valve. Another problem I’ve seen on many older vessels is the fuel jumper hose between the primary fuel filter and fuel shut-off valve has internal lining collapsed. A good way to check is install a vacuum gauge on the outlet side of the primary fuel filter. Good luck!

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+1 on fuel starvation. From the perspective of a yard tech, it’s always a clogged filter, and one of the other things when it isn’t. If you read significant fuel vacuum and the rest of the list checks out, have a look for a tank riser intake screen, another favorite, and remove if found.

Also, check that the shutoff handle returns all the way. I’ve had one stick on a 6-71, causing very similar symptoms.

all spot on and probably covers it. I just rebuilt my 3-71 …if it’s fuel pressure check the limiting orifice on fuel return line, also … governor action, … the collapsed fuel line is a good one !! … get a press guage on the fuel line, that’ll tell the tale.

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