120 omc died now not getting fuel

scott11

Seaman
Joined
Oct 1, 2009
Messages
72
Hi guys, I was out on the water yesterday testing out the new boat. It was running great for about 15 minutes then out of nowhere it started sputtering and died. After that i got it to start but it died shortly after. I pulled the fuel line off and noticed there was no fuel in it about 2 feet from the tank. Is there a fuel pump in the tank that possibly could have failed or is it just the mechanical one on the motor? Im newer to the I/O so sorry if this is a stupid question. Any input is greatly appreciated to what this could be. The boat and motor are a 1981 too if this helps.
 

Maclin

Admiral
Joined
May 27, 2007
Messages
6,761
Re: 120 omc died now not getting fuel

If the engine is all stock as it came from the factory then there is no pump in the tank, only the mechanical fuel pump on the block. It could have failed but that is not necessarily the only thing that can cause your symptoms. There is a test that can be performed, measuring the vacuum draw on the inlet side, requires a vacuum gauge. I think the adults only topics at the top of the forum has some liks to procedures for the test.

Clogged fuel filter(s). There may be one in the carb inlet. May be another inline somewhere. Have you replaced those recently (or ever!!)?

There is a fuel tank vent that can get clogged and the fuel pump will eventually vacuum lock as it tries to draw fuel out but no air can get in. Remove the fuel fill cap and listen for a rush of air, if that happens then it could be the venting. Typically though this condition is temporary and the engine could start later, like the next day, after cranking a bit. Also removing that fuel line may have released some of the vacuum, have you tried to start it since then?

There could also be an anti-siphon valve on the tank fuel outlet fitting, actually it is the fitting itself. Those are in place to keep the fuel from siphoning out in case of an accident. The internals can fail and it makes the fule harder to deraw out. Typically though the symptoms are more like not getting full RPM's and it sputtering and surging due to low fuel level in the carb.
 

scott11

Seaman
Joined
Oct 1, 2009
Messages
72
Re: 120 omc died now not getting fuel

Ok I didnt have a whole lot of time tonight after work but i checked the fuel filter on the fuel pump and the fuel/ water separator. The fuel filter in the pump was pretty dirty so ill replace both of them. There was fuel on the engine side of the fuel/water separator but the other side was dry. I tried to blow air by mouth towards the fuel tank but it seemed blocked. I was wondering is there a butterfly valve or something in the tank to block this? Or could this be a blocked vent line?

Also last night when I was cleaning out the fuel pump I found the clear vent line that goes to the carb was gummed right up with green goop. When I turned the motor over tonight it fired right away then i shut it down because it wasnt hooked to muffs. Ill have to run it on the muffs possibly tomorrow night to see what happens.
 

scott11

Seaman
Joined
Oct 1, 2009
Messages
72
Re: 120 omc died now not getting fuel

Also when i could get it running on the lake again it seemed to only want to start with the throttle pretty much backed right off. As soon as I would rev it up it would die.
 

Maclin

Admiral
Joined
May 27, 2007
Messages
6,761
Re: 120 omc died now not getting fuel

The anti-siphon valve will block you blowing air into the tank. It is a spring loaded checkball that needs slight vacuum to open, and seals shut when no vacuum is present. Seals shut tighter when anti-vacuum (pressure) is supplied.

I bet the filters are restricting the flow into the carb. It can only get a splash of fuel every so often, not enough to fill the bowl and keep up with the engine's demand.
 

scott11

Seaman
Joined
Oct 1, 2009
Messages
72
Re: 120 omc died now not getting fuel

Ok thanks guys for the input. I will have to pick up some for the weekend and then maybe take it for another test run.
 

Celtichawk

Chief Petty Officer
Joined
May 6, 2012
Messages
564
Re: 120 omc died now not getting fuel

Where is the anti-siphon valve located?

Answer from previous post of my own.....answer is located on top of fuel tank! Most obvious area that is. Copper elbo fitting!
 

scott11

Seaman
Joined
Oct 1, 2009
Messages
72
Re: 120 omc died now not getting fuel

Ok so after checking all the filters and cleaning as much of the crummy fuel out as possible it seems to be running better now. I had the muffs on last night and let it run for a while. I noticed that once it got up to operating temp and the choke opened it would die out unless you closed the choke again. I found a bunch of crap in the filter on the carb so i cleaned it right out and tried again. The boat was running great with the choke opened up now. I guess ill just have to get it out on the lake again and see what happens.

Since its so close to the end of the season I am just going to hold off on the new filters until spring I think. I just want to figure out what all is wrong with it and fix all I can before the dreaded winter comes. Thanks guys for the help on this one.
 

scott11

Seaman
Joined
Oct 1, 2009
Messages
72
Re: 120 omc died now not getting fuel

Ok so I took the boat out yesterday afternoon for a run. It ran good for a while then started to act up again. I limped it back to the marina and removed the small filter on the carb to find it was full of varnished fuel that was in an almost gel like state. Judging from hours of research im going to have to pull the tank and clean it right out. I was considering trying something like sea foam but since I boat on georgian bay and lake huron it might be in my best interest to do it right the first time.

Its kind of unfortunate being I just put in over 20 liters of gas so now I will have to find somewhere to dispose of that. I also noticed before the boat was about to stall out it would develop a good tick. Once I cleaned the filters out again it would go away.
 
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