I've had a couple of similar issues from time to time. Suction side air leaks
can be difficult as often there's no fuel drip.
One time on an old Volvo
one cyclinder, the engine
would run provided that we left the bleed screw in the top of the fuel filter
cracked open and dripping a bit. If we closed the bleed screw the engine
would stop. The air leak turned out to be a rubber fuel hose that had damaged internal wire reinforcing that had worked a pin hole in the line between the tank and fuel pump
. No drip evident. By leaving the bleed screw open, the air could escape (with a bit of fuel) and the engine would run.
Another time we traced an air leak on our Universal to a microscopic crack in the brass elbow
at the top of the tank where the fuel pick-up tube goes into the tank. No fuel leaking out just air getting sucked in.
I guess the lesson is to make sure everything is clean and tight, hoses are new, fittings replaced every few years.
On our Ericson
with the Universal, the tank had several pick-ups installed (it had a diesel
heater and a genset once upon a time). I led hoses from these extra pick-ups to a small electric fuel pump
and a valve such that I could switch pick-ups if I thought one had become clogged. I also had two Racors mounted with a valve between so that I could switch filters. This system also allowed me to replace filter cartridges while the engine was running. I ran the 2 micron filters which given our sometimes dirty fuel only lasted maybe 50 hours before they clogged up. Sometimes not even that. Putting a small electric
fuel pump in the line from the tank also allowed for pre-bleeding the system without turning the engine over. I had a switch rigged to shut off the electric pump
but I almost always left in on. Probably made life easy on the engine's fuel pump. The other cool thing about the electric fuel pump was that as it became difficult for the little guy to pump fuel, it would start thumping louder and louder ... sort of a built in alarm
that it was time to switch filters. Also as I would bleed air out of the system, the electric pump
would change pitch
, thus letting me know that I could close the bleed screw.
Nothing worse than an engine quitting just when you need it.