Engine trouble

[mwrohde]

Grrrr. Something is always broken.

Today my engine quit on me. It's a 1983 Yanmar 1GM. If I bleed the system I can get it to run for anywhere between 10 minutes and 30 minutes before it dies and I have to bleed it again. It runs less time at higher RPM. Max RPM is severely degraded.

Since I can get it running again by bleeding the air out of the system I'm concluding that I'm drawing air into the fuel line somewhere. Agree?

If that's right, are there any likely suspects or places to look?

Thank God for sails,

Matt

[Gary M]

I would say that yes, you do have an air leak. There are only so many connections so check them all. On a friends boat last fall that had the same issues, was an air leak in the fuel line.

Gary

[DeepFrz]

Could also be a partial obstruction in the fuel line. This would allow fuel to slowly enter the line, enough to run for a short period of time. When the engine stops and you bleed the system a little fuel will flow in. Check for fuel flow using the lift pump, check your filters and check all your fuel line connections.

[Faster]

Having experienced both scenarios first hand, I can vouch for the two gentlemens' suggestions above.

The good news is that it's a pretty simple system, and once you've checked and fixed or renewed any dodgy connections you should be good to go.

Things to look for - loose clamps, damaged or chafed fuel lines, old gaskets at bleed and hose fittings (the copper ones can be renewed by heating them up with a propane torch - away from the fuel system, of course!)

I recently had a crimped pickup line inside the tank, and a friend recently had a bleed screw that had cracked in such a way that he didn't notice til he attempted to retighten it after bleeding, when it broke clean off.

Minimize connections where ever you can.

[sailingdog]

It could also be a blocked fuel tank vent line. If insects, like wasps, have built a nest in the line... you can have similar problems as well.

[jrd22]

Check the O-ring on your fuel filter bowl, we have had problems there with our Yanmar(different model). Anywhere you see any wetness from fuel is a likely air leak. If you have old fuel hoses they can have small cracks in them that will let small amounts of air in also. It can be a real bugger to find a small air leak, good luck.

[Valiente]

Originally Posted by sailingdog

It could also be a blocked fuel tank vent line. If insects, like wasps, have built a nest in the line... you can have similar problems as well.

This one has caught me before. It's possible for some spider debris to actually form a flap that doesn't fully seal until the pressure in the vent line is "intaking" enough. This means the fuel pump is only gradually overcome. Turn off the engine and the suction dissipates...and you can miraculously run again.

Particularly as it is springtime, you may be victim of a wee critter having make a winter home in your vent line. Remove it from the tank side and blow out...if there is any obstruction, take it off the vent as well and blast it with an air gun. Run a dental pick (one of my favourite boat tools) out through the vent and check that you've got those little screens in. Barring that, glue down some screening over the external vent holes to prevent critter ingress.

[Omatako]

To either prove or disprove the blocked vent theory, wait until the engine stalls then quick as possible tkae of whatever fuel cap you have. A sucking in of air into the tank will tell whether the fuel pump has drawn a vacuum. If the vacuum is big enough to stop the fuel pump drawing fuel, you'll hear it.

Good luck
Andre

[foxglove]

I met a guy once who had a similar problem. He would run his boat for a few minutes then it would shut down. After a few more minutes, he could restart it but it would soon shut down again.

After several visits to the mechanic, the problem was solved. Bits of fiberglass were breaking free from the interior of the tank and floating around until the fuel pump pulled them into the intake. They would float away after the engine was shut down but block the intake again soon after restarting.

Years ago, I heard of the same thing happening to a sports car with a fuel filler positioned behind the drivfer's head. A leaf had found its way into the tank and intermittently blocked the fuel intake as it floated around the tank.

[mwrohde]

Well, I've found the problem. One of the fittings that the rubber fuel line pushes onto had come partially un-threaded. I've tightened it and am quite sure that was the problem.

I saw that the fuel line was stamped "1982" and was cracked. So, all of that has been removed and will be replaced Saturday. I'm also replacing both fuel filters. Finally, since I was in that tight space and smelly already, I drained the engine oil and will replace that Saturday, too.

Now for the follow up question.

Do I have to replace the fuel line with marine fuel line? The existing line is stamped "nautical" all over it. My thinking is that automotive line should be fine. I day-sail on a lake with tons of boats on it all the time, so help is always available. Surely new automotive fuel line is safer than 25 year-old marine fuel line. My big reason for pushing this is I'm betting that fuel line from the auto parts store is tons cheaper than from the marine store.

Thanks