Causes of Recurring Vapor Lock

[Terra Nova]

Hoof--good post.

[Scout 30]

Pretty common for fuel tank vents to get plugged by bugs. An easy way to see if that's the problem is to crack your fill cap. If you haven't changed your fuel filters you need to do that first. Before you do that head down to your neighborhood auto parts & get an electric fuel pump. Install it on a bulkhead with a fused on/off switch. This will make changing filters & bleeding your system very easy plus it's a back up fuel pump. A Racor filter with a pressure gauge is handy although kind of overkill for a motor this small. If there's a leak in your fuel line the electric pump will help you find it. Important to note that even with a small leak in your fuel line your engine will run with the electric fuel pump on but you still need to fix the leak.

[DH777]

Wow. I never expected so much response in less than 24 hrs. -And, it all look like very good stuff. I had been thinking of asking where the fuel tank vent is because I get plenty of mud wasps everywhere. There is really a lot of good advice and leads here.

I am really thankful for everyone who replied. I hear the 'patience' advice loud and clear. That is a commodity I typically don't like to expend, so I will do some of the obvious leads I have received here before breaking every B-nut, clamp, hose and fitting.

It seems like some in the sailboat community has some pent up frustration surrounding this issue. I hope it benefits many, and gets us out on the water...

DH777
New Orleans, LA

[Cadence]

Check your tank vent for mud dabbers. if your boat is moored anyplace close to shore.

[Scout 30]

Mud Daubers are the bane of fuel tank vents. Make sure your vent has a screen.

[westwinds]

I once had a problem like this. There was a coupling on a copper pipe where the hole through the coupling was a little smaller than the pipe. Insects somehow got into the fuel tank and came up against the reduced diameter of the coupling. Would run fine for about 20 minutes, engine stops, wait 5 minutes, starts just fine, goes about another 20 minutes, etc. I had this happen on another engine and just blew air backwards into the fuel tank which took care of it. Be sure to remove the filler cap if you blow air into the tank through the fuel line.

[TrinitySeas]

I have had a similar set of problems as discussed here, multifaceted problem included dirty fuel and clogged filters, a vacuum gauge that gave false readings, sucking air upstream of the Racor first stage filter specified to starboard tank by switching tanks. Short term/emergency solution = clean diesle in jerry can and drop first stage intake into that can then bleed the air from the engine. I am exploring TRANSPARENT fuel line for an upcoming overhaul and am reading that Tygon tubing may be suitable; see here,f or example:
Where can I get clear fuel line?
5/16" I.D. TRANSPARENT FUEL LINES - 5/16" Fuel Line - Fuel Line - Tubing & Hose - Products

Maybe it will turn brown/translucent after a few years (?), but I'd prefer that to the opaque/rigid/stiff conventional fuel line. The latter is also very tough to work with/tough put onto a barb fitting, yes?

teh suggestion of an electrical pump is good too; this can also permit bypassing of the mechanical lift pump in case the latter fails. Simply engage the electrical pump, run the fuel from a very fine (2micron) primary filter directly to your secondary filter or intake for injector pump. You'll pump in more than you need, but the fuel return will just keep things humming along.

[Old Swampy]

I concur with CheeChako and Hoofsmit; look at the very upstream part of the fuel line, the pickup tube in the tank. On a boat new to me the engine died right after launch and departure. Turned out the screen on the pickup tube in the tank was clogged solid with black scum that had hardened. That boat is headed for a dumpster for many reasons.

[Compass790]

I agree with hoofsmiths suggestion except I would feed the fuel straight to the injection pump first & then go back to the lift pump. You can just get a 1.5 litre plastic Coke bottle & silcone a bit of plastic tubing into it & gravity feed your injection pump. Or you can get electric fuel pumps online from China for very little to do your testing. First I would clean the tank vent as suggested tho & the tank & lines as well if it isnt too much of a ball ache. We had similar problem in our YSM 8 & it turned out to be a filthy diesel tank that even had leaves in it! I suspect stuff was getting sucked into the inlet tube & completely blocking it when the engine was running at cruising speed. I found you can just anneal all the copper washers on your fuel lines rather than pay the ridiculous yanmnar part price & that works good. You can just do it on an old fashioned stove element if the wife isn't watching or on the boat stove. Good luck

[Lepke]

I had a pin hole leak in a fuel line that gave very similar problems. I didn't find it until I did a pressure test on the line.

[slowpoker]

Yes, a pressure test will tell you everything and solve future problems besides.
An electric pump, on the fuel hose between the tank and the first filter will pressurize the whole system to test for weeping fuel anywhere.
Also, if you disconnect the fuel line before the first filter, pumping diesel into a container, you will know if the flow is good, or good for a short while before it slows down because it is being starved by a clogged tank pickup tube or vent.
The electric inline pump is cheap on ebay, easy to install, will get you going even if the engine's lift pump quits and you must by-pass it (keep a 1/4" hose barb connectorand clamps in your spares box) and will always help you to bleed the lines without running the hot engine whenever needed. Good luck.

[Cap Erict3]

Originally Posted by slowpoker

Yes, a pressure test will tell you everything and solve future problems besides.
..........
The electric inline pump is cheap on ebay, easy to install, will get you going even if the engine's lift pump quits and you must by-pass it (keep a 1/4" hose barb connectorand clamps in your spares box) and will always help you to bleed the lines without running the hot engine whenever needed. Good luck.

Second this. A mechanical lift pump goes out due to an internal check valve or a hole in the pump diaphragm.

A hole in the diaphragm will also cause your oil level to rise.


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Looking for another pretty place to work on the boat.