Mercury Racing 700's Very Hard to Re-start
10-29-2011, 08:31 PM
#21
Registered
Bob Teague replumbed my fuel system with a return to tank. Thats the ticket on 700's. The reflash helped but the replumb solved it. I think he is now selling a kit.
10-30-2011, 01:39 PM
#22
I had a similar issue with my old 540 EFI. It is definitely vapor lock, and occurs due to the following factors:
1) Ambient temperature
2) Engine compartment temp (after a hard run)
3) Fuel filter placement (how high above tank level)
4) Minor leaks in the fuel filter seal.
5) Rocking and rolling while anchored or docked (tends to help break the vacuum, and let the filter contents drain back to the tank.
6) ability of fuel pump to self-prime (most are very bad at it).
7) Return or returnless fuel system (returnless or return to filter don't prime well by themselves at all).
If you have fuel pressure gauges, you know exactly what's happening. I ran into situations where I'd get air into the filter body. Engine would start up and run on what was left in the pump and rails, but then quit after a minute. Other times, it would lose prime entirely after sitting and get no pressure at all to start.
Solution was to disconnect fuel tank vent, and press up fuel tank to a low pressure using a raft pump (or blow into it in a pinch...). Once holding some pressure, I'd crack the fuel filter open, and allow it to fill from the tank. Shut everything back up, and reconnect the vent, and you're on your way. Once the fuel pump can grab at least a little bit of fuel to get things moving, then you are in good shape.
1) Ambient temperature
2) Engine compartment temp (after a hard run)
3) Fuel filter placement (how high above tank level)
4) Minor leaks in the fuel filter seal.
5) Rocking and rolling while anchored or docked (tends to help break the vacuum, and let the filter contents drain back to the tank.
6) ability of fuel pump to self-prime (most are very bad at it).
7) Return or returnless fuel system (returnless or return to filter don't prime well by themselves at all).
If you have fuel pressure gauges, you know exactly what's happening. I ran into situations where I'd get air into the filter body. Engine would start up and run on what was left in the pump and rails, but then quit after a minute. Other times, it would lose prime entirely after sitting and get no pressure at all to start.
Solution was to disconnect fuel tank vent, and press up fuel tank to a low pressure using a raft pump (or blow into it in a pinch...). Once holding some pressure, I'd crack the fuel filter open, and allow it to fill from the tank. Shut everything back up, and reconnect the vent, and you're on your way. Once the fuel pump can grab at least a little bit of fuel to get things moving, then you are in good shape.
