Mercury Racing 700's Very Hard to Re-start
 

All three 700's are very hard to re-start. I ran with Ft. Meyers Offshore today and almost could not get any engine to re-start after lunch. This has been getting progressively worse. I can shut off an engine briefly, and it is a little difficult to restart, but if I let it set for a couple of hours … forget it. I went after the easy stuff, new fuel filters (primary and secondary), new flame arresters, and I just recently changed one of the idle air control valves. No luck so far. 600’s on the Formula start like they have a pilot light.

This Donzi has a strange fuel system. Three tanks with two electric transfer valves. I can run either off of the two side auxiliary tanks or the main center tank. The transfer valves feed a common manifold that all three of the engines are plumbed into. The engine keys are under the back seat. There is an ignition switch and an engine crank switch at the helm. I have fuel pressure gauges and I noticed that the fuel pumps only kick in for a couple of seconds after the ignition switch is trigger and the pressure bleeds off quick. I thought that maybe I was waiting too long before I crank the engine, but it doesn’t matter.

The engines start up fine first thing in the morning with some cranking, but nothing like the lightning fast fire up of the 600’s on the Formula.

Any ideas???

Thanks,

Andy

Mine crank instantly. With fuel injection, you would not think you would have to crank long in the am if all was right. Let us know when you figure it out. Good Luck!

Heat Soak?
 

Not sure of your plumbing description on the Donzi, but the telltale for me is that you say the fuel pressure bleeds off quickly after shut down or key off? Does the bleed off happen as fast when the engines are first time keyed cold or stopped??
Fuel injected engines need good fuel pressure right when they are first cranked for starting and low fuel pressure will almost always result in slow to start fuel injected engines at start up. I would look at the fuel pressure regulators and see if heat soak maybe causing them to bleed the fuel pressure off to quickly when the engines are warm and then stopped. This heat soaking of the fuel system could be caused by not enough of the regulator bypassed fuel getting cooled quickly enough or long enough after runs and then going back to idle for docking etc. Just some ideas.

Best Regards,
Ray @ Raylar

What is the fuel pressue while cranking?

Vapor lock, fuel turning into vapor, creating a vapor/gas bubble at the injectors that just takes a lot of open injector time to purge through. Try to see if this gets better if you are able to get some heat out of the engine compartment after shutting down and before trying to restart (e.g, get the hatch open early before you dock and shut down). If all three are doing it, it seems more environmental than a specific issue with the engine(s).

Thats what Im thinking too....Open the hatch and let the engine campartment cool down...

+2.

Solved a similar problem by simply lifting the engine hatch while we ate lunch. It's worth a try.....

You can also try running the engine compartment blowers. The behavior of the fuel pumps seems normal- there is a safety switch on most electric fuel pumps that cuts the pump if oil pressure drops below about 3-5 PSI. If you look at your oil pressure sending units, you probably have at least 2 wires- one is to the guage, the other to the fuel pump.

Ive watched this happen to guys with the 700's too. They let them idle for a few minutes before shutting them off... Seems to help.

if all three engines are doing the same thing,,,,what are the common factors of all three engines,,,that fuel manifold sounds like a good start to me,,,,maybe be one of those transfer valve is stuck open, when it shouldnt be ,letting the fuel bleed down,,,,id cycle the sh$t out of those transfer valves,,,then try getting all the engines running off one tank,,,