Motor shut off twice, ran it for 4-5 hours straight

Jlomb436 · 24 July 2017, 05:37

Hey everyone.

I had SUCH a fantastic day out today. Water was glass and for the first time in awhile I was able to get my boat to plane at 15-20 mph all day. Went 60 miles up and down the coast!

However, I did run into some issues while out. After about 4 hours of running, my motor simply died. It felt like it was winding down, so it took about 2 seconds to shut down. I tried restarting but it wouldn't have it. After waiting about 5 minutes, started right up.

30 minutes later, same thing. Died and after 5 minutes, started up. Performance seemed fine. What does that sound like to you? The motor? Fuel? This may sound ridiculous, but I'm assuming you don't need to re-pressurize the tank after a few hours?

It's a 1988 Mariner (Yamaha) 15 hp 2 stroke. I took it to the shop a year ago for a tune up. Guy said it looked fantastic but replaced the impeller due to it being 29 year old rubber. The motor was originally used for about 10 hours and then stored (indoors) for 29 years.

The only other item I would mention is sometimes it makes a gurgling or clanking sound but it's off and on. It doesn't sound like a piston knocking to me, but my knowledge of outboards is lacking. I will likely take it to the shop, but I'd still love to hear your thoughts.

phoenixpete · 24 July 2017, 08:55

Sounds a bit like it is running out of fuel, the petrol tank is vented right?
You should have a little vent screw on the tank in the cap, this should be open to allow air in or it will cause a vacuum which will make the engine cut out.
Sounds like it starts after some air has managed to get back in.
Sorry if you know this but people do sometimes forget to open the vent.

Stevie Bill · 24 July 2017, 10:11

And.. The vent screw can vibrate itself shut! Happened to me this last weekend. Ran great for an hour or more then died of fuel starvation. Reopened vent screw, big inhalation from the tank, repump the primer bulb and no further issues...

Jlomb436 · 24 July 2017, 19:08

Well that is em-barr-assing.

Honestly, I thought the valve cap was simply a safety measure so the tank didn't explode from expansion. I leave it open in the garage, otherwise during towing or boating I turn it hard right until it's closed. I feel like an idiot.

Each time I actually released the pressure from the tank and primed the bulb again. Now that I think about it, I could remember hearing air come in from the line connection to the motor. That's probably the only way air could get in with my valve closed.

I'm guessing that's what it is...

Could it be anything else that I should check just in case? Should the motor be able to run all day? Being a 2 stroke and from the 80's, I can't imagine it has any electronics monitoring temperature, right?

two stroke mick · 24 July 2017, 19:17

Every day is a school day

Stevie Bill · 24 July 2017, 19:54

And... SHUT the vent when storing to prevent atmospheric moisture getting into your fuel and maybe causing corrosion or other problems later!

paintman · 24 July 2017, 20:53

When using the boat the vent must be open.
If not you are creating a vacuum in the tank as fuel is drawn.
Potentially - esp with a metal tank - it could collapse the tank.
Perhaps not as spectacularly as this one but it isn't unknown on cars if breathers are blocked:

https://www.youtube.com/watch?v=UpWeU2fvFGs

phoenixpete · 25 July 2017, 15:43

Quote:

Originally Posted by Jlomb436

Well that is em-barr-assing.

Honestly, I thought the valve cap was simply a safety measure so the tank didn't explode from expansion. I leave it open in the garage, otherwise during towing or boating I turn it hard right until it's closed. I feel like an idiot.

Each time I actually released the pressure from the tank and primed the bulb again. Now that I think about it, I could remember hearing air come in from the line connection to the motor. That's probably the only way air could get in with my valve closed.

I'm guessing that's what it is...

Could it be anything else that I should check just in case? Should the motor be able to run all day? Being a 2 stroke and from the 80's, I can't imagine it has any electronics monitoring temperature, right?

We like the easy one's. Glad you got it sorted