Engine dies after running for several minutes

[bbook83]

The points have not been damaged. I got the new resistor wire and installed it. I now get an even higher reading at the plus side of the coil at 11.8 volts (was 11.6 with the original resistor wire) when running. I was hoping for about 7 to 9 volts. I removed the tan wire (origin at starter) from the plus side and the engine starts without it, which I suppose is expected, given the voltage from the resistor wire. it Is very windy and rough, so I cannot go out and put it under load and see if it stalls, but with that voltage, I expect it will. I have attached a picture of the wiring diagram, which tracks with the wiring in place. Any more ideas out there?

 

[bbook83]

I tested the boat on the lake under load
with the new resistor wire and continued to experience stalling. At one point I heard popping noises like you might hear on an engine cooling down, but the engine was not overheated. I disconnected the fuel line at the carb and cranked the starter. No fuel came out for the first second or so, but then began surging from the fuel pump. I reconnected the fuel line and the engine ran great without stalling as I returned to the dock after about 20 minutes running time, longer than it has for two seasons. At the dock, I shut it off and restarted easily twice, with no issues. I did not have time for further testing, and won’t be back to the boat for a week. Does this sound like vapor lock?

 

[alldodge]

Not VL, something with the fuel supply
Look into the tank antisiphon valve, fuel lines, pump and fittings

 

[bbook83]

I think you are on the right track, Alldodge. The fuel pump has been replaced & line to carb has been replaced with a PFTE line. The anti siphon valve is clean and moves freely, but perhaps there was back pressure against it that was released when I removed the fuel line. But, was the back pressure from vapor lock? A photo of the valve is attached, showing it being held open. I will remove it and run without it for a test and will report back in a week or so. Thanks for the help.

 

[alldodge]

That pic is not a antisiphon valve and has no business in my opinion in the fuel line.

 

[bbook83]

That pic is not a antisiphon valve and has no business in my opinion in the fuel line.

Interesting. When I first pulled it, I was expecting a ball type valve, but it seemed functional, so I left it in, with some input from the forum in another thread. When I am done testing, I will install a new valve. Online, I see Moeller valves as part of a hose barb fitting, but you can’t see the valve in online pictures. I assume they are a ball valve.

 

[alldodge]

Yes, its a ball valve

 

[flashback]

That pic is not a antisiphon valve and has no business in my opinion in the fuel line.

Wondering what it is, looks like something for an air compressor..or sprinkler system..

 

[alldodge]

Reminds me of something that might be on the output side of a mechanical fuel pump. Keeps fuel from draining back thru the pump when shut off, but just a guess

 

[flashback]

I can see that! I wonder how much pressure it takes to open it?

 

[bbook83]

I can tell you that it failed the “Suck Test” suggested by some, in that I was unable to open it by sucking on it with my mouth. Being the original owner of this ‘74 Jolly Roger, I can also say that the valve was put there by the boat manufacturer when the boat was built, although back then they were just another short lived boat builder. Still, the fuel pump is able to open the valve till about 5 or 10 minutes after startup, so something is creating a back pressure of some kind. I guess I may find out when I run without it.

 

[bbook83]

I purchased the hose barb fitting with a ball type check valve shown in the picture below. It passes the “suck test” and moves more freely than the original. Thanks for the guidance on this item.

 

[bbook83]

I installed the new anti-siphon valve, but the stalling continues. I finally removed the fuel hose from the barb at the tank and stuck it in a gas can and it runs great without stalling. I ran it under load it for 35 minutes and it never stalled. I am obviously having a problem at the tank. I siphoned the remaining fuel in the tank and stuck an endoscopic camera down from the gauge sending unit opening and the take up opening. I see some debris, but I don’t think I can get it out unless I can get a suction line down it. I am not convinced that it is clogging the take up, but don’t mind trying to get it out. The take up tube is always clear after the stalling. I have removed the vent hose from the tank and blown air through it, which exits out the through hull opening. I will keep chasing this, but would welcome any other ideas.

 

[Fun Times]

Sometimes the fuel pickup tube can get a fine crack/split and suck air... at certain fuel tank levels too.
Or the pickup screen gets clogged up.
This debris was found recently inside a tank,

Black Scorpion Mag Mpi fuel pressure

According the 24 service manual I am supposed to be getting 34-38 psi. Is that at idle with regulator vacuum connected? I'm getting 26psi at idle with regulator vacuum hooked up. If i disconnect the vacuum should it increase? I'm to determine if I have a fuel or regulator issue. After a few...

forums.iboats.com

How much fuel is inside the tank? does it seem to have issues both while low and full of fuel?

 

[bbook83]

The issues exist full or low of fuel. The take up tube is copper, soldered to the elbow fitting. I have blown through it without noticing restriction or leaks, but will re—check. I bought a new Moeller take up, but the male end into the tank is 3/8 NPT, and mine is 1/4 NPT. I am searching for the right one. The way it runs ok for a while makes me suspicious of venting, but I have blown compressed air though it, as previously noted. Thanks for the old thread. I thought I had read everything on the topic, but missed that one. I would love to find a simple answer like that.

 

[bbook83]

Well, with the endoscopic camera, I found what looked like a piece of the Por 15 tank sealant system I applied to the tank several years back that had flaked off due to rust underneath it. It was on the tank bottom directly below the pickup tube. I sucked out everything I could from the empty tank with a small shop vac, and the flake was no longer where I had seen it. I obtained the correct plastic pickup tube and fitting, cutting the bottom at at a 45 degree angle, with the point about the same length as the original copper tube, which was smaller diameter, and cut at 90 degrees. I put 5 gallons of fresh gas in the tank and ran the boat on the lake for a half hour without any problem, leaving the fuel gauge sending unit out so I could put the camera through it to see any obstruction that might have been there if the engine had stalled, bit it didn’t. Back at the dock, I checked with the camera, and there was no debris and no obstruction, so I closed up the sender opening and ran it one more time, to be sure the uncovered opening was not creating a vent, if that was my problem. No problems on that final run. I suppose debris could be a problem in the future, so I will see what a new tank will cost, which will likely have to be a custom build.

Thank you to all who assisted me with responses in this thread, when I was chasing both ignition and fuel issues. Sorry, this is long, but I thought it would be good to let you know how it turned out.