You say you have low fuel flow out injection pump to lines, this can happen if your shutdown lever is not returning all the way to full off position for fuel, and a sticking fuel rack inside injection pump, this is why I asked if this has been sitting for some time which causes rack to freeze in no or little fuel position, seeing you had algae growth it tells me it has been sitting, if this is the case fuel pump needs to be replaced.
The only other thing that would cause this is low fuel pressure to the pump or air in fuel before the pump.
You can use a site glass before injection pump to see if you are getting air in fuel to pump, or run a line from fuel transfer pump directly into a container of fuel (5 gallon bucket) and see if you have a issue before pump restricting flow or getting air.
To me it sounds like rack is stuck inside injection pump which means injection pump needs to be rebuilt.
When you hold throttle in full fuel with one hand and move shutdown lever in other you should feel them fighting each other.
Midwest fuel injection can either rebuild yours or they have common pumps they have available for exchange so no waiting.
Click here for their web site to order rebuilt pump or get a exchange.
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