Sadly, we have moved to a harbour with fewer old boat guys to help us

June 23, 2024 2:24 PM

Twice now, when coming in to dock our boat, our outboard motor (a Yamaha f5a) has died on us. Today, thankfully, the wind was at our back and we were able to gently drift into the slip. However, obviously this is not always going to be the case, so we should probably get this figured out.

We bought a small boat last year (classic Swedish Maxi 77) that seems broadly to be in good shape. Included with the boat was the relatively recently purchased outboard motor, a Yamaha F5A. All of last summer, the motor caused us no issues, but since we started sailing again this year we have seen on both times we have been out issues with the motor when we come back in to harbour.

Symptoms and details:

* The motor sometimes revs up and down a little instead of being at a gentle, steady purr
* It has only cut out as we come back into the harbour, meaning we are at a low speed.
* The motor uses an external tank which has plenty of fuel, although it might be a bit on the old side.
* The first time that it did this, we use the bladder to try to pump fuel into the engine, and it restarted immediately.

We looked at the fuel filter last weekend, and followed the recommendations in the manual to start the motor and it broadly seemed fine. The fuel filter looks pretty clean, which matches it being a pretty new motor.

If I had to guess, there is something wrong with the fuel line and it is not drawing enough fuel. But that is really just a guess as I have never owned either a sailboat or a motor like this before, and I really don't know what I am talking about. Please pretend I am very uninformed and lack skill and knowledge, since that is pretty much the case.

posted by vernondalhart to Sports, Hobbies, & Recreation (10 answers total)

There’s lots of things it could be, from old fuel (which you’ve identified yourself), to the fuel pump, to a dirty air filter, to the sparkplug, to the carburettor being clogged, but the bigger question is: how often are you running it, and how often is it getting serviced? If you haven’t had it serviced since you bought it last year, and you don’t know when the previous owner had it done last, that’s where I’d start.

Small petrol engines like this one benefit from getting run frequently and serviced, more often than you think.
posted by Fiasco da Gama at 3:11 PM on June 23 [2 favorites]

My old outboard would die because while sailing, the fuel hose would kink as the (external) fuel tank shifted around from tack to tack. The kink was just enough to starve the engine of fuel and it would die, usually right when I needed the engine most. Also, maintaining that thing meticulously went a long way towards keeping it reliable.
posted by niicholas at 3:21 PM on June 23 [2 favorites]

Like all gas engines, fuel, air, spark. Since it runs at all I'd say spark is fine.

When you say the fuel filter looks clear I'd guess you mean the fuel water separator. That's not really a filter, it's for keeping water out of the engine. If you follow the fuel hose under the cowling you'll see a tiny little fuel filter. Change that thing. All the time.

I'd guess bad gas and a fouled filter.


And although I do live on a boat I don't consider myself old just yet.
posted by chasles at 4:51 PM on June 23 [3 favorites]

Leaving unstabilized fuel in a gas tank, and the other parts of the fuel system and engine, over the winter is pretty much a recipe for this kind of thing to happen. It always happens with, for example, lawnmower or snowblower engines that are left sitting for many months.

Here is a thread with a lot of ideas & suggestions for dealing with this situation, both in terms of preventing it and dealing with it once it has occurred.
posted by flug at 8:59 PM on June 23

This sounds like a fuel issue and I suspect it's either a blockage in the filter or line or a blocked vent in the fuel tank. Given it resolves by squeezing the primer bulb, it's most likely a blockage in the line, but a blocked vent will give you the symptom of seeming like it's running out of fuel only after operating for a while and will then run perfectly once it's managed to suck some air back into the tank (likely by someone taking the fuel cap off to see if there's any left).

You could try running the engine with the fuel cap removed if that's safe - this will eliminate or confirm the blocked vent. A problem like this is best diagnosed while at a dock or at anchor, obviously.

It's slightly possible the fuel is bad, so my first step would be to replace the fuel if only to eliminate that.
posted by dg at 10:12 PM on June 23

Possibly air getting into fuel line. You should always pump the bulb (bladder) before you start the engine. It should be rock hard. No harm to get it serviced. Make sure to bring fuel tank and fuel line as well as the engine.
posted by night_train at 1:19 AM on June 24

You could try running the engine with the fuel cap removed if that's safe - this will eliminate or confirm the blocked vent.

Oh ya. This is good. Sorry to assume you're new boaters but does if the fuel tank is one of the plastic type ones do you know that the lid provably has a twisty vent that you need to open when running and close when not??? Some pop up, some twist, some are just separate little caps... This would really explain the issue perfectly. The bulb would force fuel but the fuel pump will never overpower the mild vacuum.
posted by chasles at 4:21 AM on June 24

Response by poster: I should have mentioned: the bladder last year got hard when pumping, but this year it does not at all, no matter how much we pump it.

Regarding the vent: we have been opening both the one on the external tank and the internal tank when we are using the motor.
posted by vernondalhart at 12:15 PM on June 24

That sounds like an airlock in the fuel line. Try removing line from engine and holding the pin valve open with a screwdriver while pumping the bladder until fuel comes out. The Bladder should be hard now. If this keeps happening you might need a new fuel line.
posted by night_train at 1:08 PM on June 24

Response by poster: Ok, we just tried that and the fuel comes out immediately, but the bladder does not get hard.
posted by vernondalhart at 9:06 AM on June 26