tewks

I just switched over to electric fuel pumps on my carb'ed merc 330's. Had recurring problems with the belt driven mechanical pumps, they failed every two years, and thought this conversion would eliminate that worry, as well as making for easier starts. Anyway, started up the engine, no problem. Then as I was working my way into the engine compartment to check/set the timing, the engine stalled. Odd... I thought I might have bumped the distributor on the way, so I played with that but it wouldn't fire. So then I sat there scratching my head for 2-3 minutes and decided to pull off the flame arrestor to check the choke, and what I saw scared the hell out of me... The float had picked this particular moment to stick (probably dirt that got into the lines during the install), and the electrical pump was still running! The engine stalled because it was flooded, and at this point, it was hydro-locked (or gasohol-locked) from all the gas that had been pumped into the manifold.
I know on fuel injected engines, the fuel pressure is always there, I suppose you could have an injector stuck open which would cause a similar problem, but this seems undesirable to say the least. With the mechanical pump, a stuck float may make you run rich, but the volume of fuel probably isn't going to overwhelm to the point of killing the engine, and if it does stall, the flow will at least stop!
So, how do I wire up the pump to have it only run when the engine is running, but also run before the engine is started?? I had a volvo carb'ed engine that used an extra output on the alternator to trigger a relay to run the pump, but that was a different kind of alternator. Anyone have a neat way of doing this? And (should have asked way earlier...) any coast guard regs on using electric pumps?

88Fount33

You should install a oil pressure cutoff switch, such that with low or 0 oil pressure the fuel pump relay is not running the pump. Then for starting, there needs to be a connection to the starter circut to provide power to the fuel pump while you crank the engine. (Once the motor turns over a few times it should build enough oil pressure to keep the fuel pump running for a few seconds even if the motor does not fire right up, so that on a "dry start" as in you haven't run the boat in a long time and the carb is low on fuel these extra seconds will fill the carb and allow you to start the engine.)

Or you could wire in a direct feed (Ign. on circuit) to the fuel pump relay with a dash mounted toggle switch that you can turn on the pump prior to cranking the engine. I do not recommend this as it is too easy to forget to turn off the switch once the engine is running and the pump is running from oil pressure cut off switch.

rdoactive

Get a Sierra catalog, or go to a marine dealer. Get a "Hobbs" switch. It comes with a wiring diagram described by 88Fout. Sierra makes a "marine" Hobbs switch, just in case that matters, to prevent exactly what happened to you.
Gary

Wobble

What was the problem with the belt driven pumps?

Electric pumps can be a PIA, they are not reliable unless used with a return style regulator.

Your example is one of 3 similar ones I have heard of in the past six months, in one case, a twin engined boat put 6" of gas in the bilge when limping home on one motor.

I have found the belt driven ones to be very reliable and easily modified for more flow. Important to make sure there is gear lube in the housing where it bolts up.

No offense, but electric pumps are not what I would run on a stock package.

tewks

I actually regret making the switch, I may just switch back. The problem with the belt driven pumps is that they failed every other season. I bought the boat spring 2002, it was 4 yrs old. At that time, both pumps were bad, the reservoirs had fuel in them. So I replaced them, they were fine through 2002, 2003. Starting the season in 2004, again both reservoirs had fuel in them! Thinking, what, bad gas?? So I replaced them again. Fine through 2004, 2005, then this spring, both were bad again. In the larger scheme of things, spending $300 every other year to replace the pumps isn't a big deal (especially now when a fillup is over $800!), but it was just a pia. Plus the reservoirs are damn near impossible to reach (v-drives...), and I was feeling more and more compelled to check them often. The oil-pressure switch sounds like a good idea. Thanks for the suggestion!

MOP

It is a very good idea to also add a pressure regulator, engine driven pumps speed is governed by engine RPM the faster the engine turns the more fuel it supplies but and electric pump runs full volume/pressure all the time.

Phil