Fuel Starvation

Fuel Starvation May 12, 2015

By: Brad Roberts
from issue 28-1
I have a 115 hp Evinrude on a 19 ft runabout.  At the end of last season, the engine would lose power at full throttle.  Everything was fine up to 4500 rpm (our regular cruising speed of 35 mph), but when I went to wide open throttle, the engine lost power rather quickly and would stall unless I throttled back.  After a few seconds at idle though, it ran as before.
It felt to me like fuel starvation and I told the mechanic when the boat was serviced last fall prior to winterizing.  I had the dealership service department write it down on the work-order along with an explanation of what the problem was, but this past May, the problem was still there.
Is there anything I can do myself to check this out?  What is the most tactful way to get problems like this handled by the mechanic?  We keep the boat in the water all summer and it is inconvenient to haul it out and trailer it to the dealership.
D. Field, via email
The problem you are experiencing definitely sounds like fuel starvation.  There are several things that can cause this.  Here is a brief run-down.
1]  Check and replace fuel system fuel filter?
2]  Is the engine running off a built-in fuel tank?
3]  If so, try running off a portable fuel tank.
4]  If the engine runs fine now, check that the vent to the built-in tank is clean.
4]  Remove the fuel filler cap on the built-in tank to test.
5]  Check the anti-siphon valve at the fuel pick-up, remove valve and retest.
6]  If the engine works fine, replace anti-siphon valve.
7]  If the problem still occurs running on the portable tank and the filters have
been changed, then I would suggest having your mechanic clean and service
the carburetors and check the fuel pump pressure.
Most of these items you can check yourself, and even if it does not solve your problem, it will give your mechanic a head start in diagnosing you engine.
I have a Sunrunner (classic 320) equipped with twin Volvo Duo prop 570 engines.  It also has an air conditioner and a 3kw Onan generator.
Many times when using the boat, the batteries will goes dead, even when we are just using the accessories.  We are then unable to start the engines.  It looks like all the batteries are hooked together.  Some people have suggested I get a battery selector switch, but I would appreciate any help you can give me.
P.  Bathillette, via email
The electric problem you are experiencing definitely sounds like the batteries are all hooked together.  The only cables that all the batteries should have in common are the negative ones.  The exception to this may be the generator, as sometimes they have two, 6 volt batteries wired in series.  If the generator only has one 12 volt battery then its ground should also be joined to the others.
The ways in which the positive sides of each battery is wired may vary a lot from one boat to another.  The best way I have found is to keep each engine starting battery separate for each engine only and have a large deep cycle battery to run the accessories on the boat.  This battery can be charged from one engine using a battery isolator when running and with a built-in charger when the boat is plugged in to shore power.
This way, the engine batteries never go dead while sitting over night.  If you use a lot of electric current while away from shore power the deep cycle may go dead, but the engines will start and as soon as it does your deep cycle will start to charge again.
Also, if you have the built-in charger wired in to the AC circuit on your boat, you can charge the deep cycle accessory battery by running the generator as well.
One other point, if your galley fridge is a combination 12 volt DC/ 110 volt AC unit, you would be wise to disconnect the 12 volt DC circuit from the fridge.  It is the biggest single draw on the accessory side.  You can run the fridge from the generator on 110 volts AC by turning on the generator or by having the generator run in the auto-start mode. The 12 volt DC fridge is the most common reason that boat batteries go dead while sitting overnight without any shore power available.

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