Fuel tank issue

C

carvrmariner

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Joined
Jun 13, 2008
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30239
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Hello everyone. So here's the setup-apologies in advance for the long thread. I have 2-100 gallon tanks feeding big block vintage 1989 Crusader engines with carbs and mechanical fuel pumps. For some unexplained reason, the port tank feeding the port engine would quit running even when there was 25 gallons left in the tank. I had it in for service last winter and after performing extensive surgery on the port engine, they reported that the port tank was empty-I had added 25 gallons to the tank prior to cruising over to the shop so I was puzzled. They had even put a hand pump on and could not draw gas up to the carb, so they switched the selector switch to the starboard tank and the engine started. After passing my first-born over to them to cover the invoice for the work, I cruised back to home port-switching the selector back to the port engine drawing from the port tank and everything ran flawlessly. I have replaced the fuel pump thinking that was the issue, pulled the 2 pickup tubes (one for each engine) in the tank and they check out fine. I had switched the selector switch so both engines were drawing from the port tank to even up the amount of fuel in each tank last weekend and while coming home from a day out, the port engine quit and less than 5 minutes later the starboard engine quit. Switching back to both engines drawing from the starboard tank, both engines started up. I am at a total loss as to what the issue can be. Any suggestions about what to check or look at now would be greatly appreciated.
:banghead:
 
It the selector switch 100% operable? Debris in the line(s) somewhere.
Just read a thread elsewhere where the screen on the pickup tube functioned at low speeds, but, at high rpm's, would clog with 'sludge'. Back off, sludge dropped off, and it worked again. Removed the screen and all was A-OK.
 
Most gas boats have anti syphon valve at the top of the pick up to prevent leaks in case of a leaking hose. Make sure it doesn’t stick.
 
It has to be a problem with the fuel in the tank, a problem with the plumbing between the tank and the motor, or a problem venting the tank. Venting is the easiest to check - run it with the fuel cap off, and if that fixes the problem, it’s a venting issue.

do you tanks have anti-siphon valves on top of the pickups? They are very common, and commonly fail. Sometimes you dont even know you have them, because they are disguised as normal fittings.

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you can TEMPORARILY remove it, replace with a standard fitting, and if your fuel flows, then you know it was the Anti-siphon Valve.

next is to run another line ( temporary, just a piece of fuel hose) from the pickup to the motor. And if you are still having problems, time to start looking hard at the fuel, and it it’s been contaminated with water.
 
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Thanks for all the suggestions! I believe the fuel tank vent is operational as I have a whistler on the vent which sings as I fill the tank so I believe that isn't the issue. If it was the selector valves, I would think it would be an issue all the time rather than when the tank only has 25 gallons left. The pickup tubes did have a screen on the bottom which came off both tubes as I was trying to get the tube out of the threadolet-I had fashioned some screening many years ago as I was having problems with sludge clogging up the AS valve. When I checked the AS valve when I removed the tubes, they both looked fine-I had replaced the primary AS valve for the port engine about 9 years ago when I had the sludging issue. Again, both engines using both tanks work fine until the port tank reaches about 25 gallons. In addition to the oil filter-size filters for each engine, the engine has a smaller filter mounted at the rear of the engine and the carbs have the stone filters at the fuel inlet. The fuel lines are all original-please don't shame me for that-but if there was an issue with the fuel lines, I would think it would be at cruise which doesn't happen. Again, I cannot grasp what the 1/4 tank full would cause the fuel starvation issue. Please keep offering suggestions.
:banghead:
 
I would think the vent still might be a possible as air flow is different filling vs drawing. I would try isolating every section of flow and try to narrow things down, very strange, good luck…
 
Could, possibly, the pickup tubes be sucking a bit of air if you're bow up and tubes are facing forward? Can you extend or move tubes to face aft?
 
I would run it without the gas cap, just to 100% eliminate the venting components.

if it dies at the same level every time, my guess is that is has to be a hole in the pickup tube, right at the level the tank is getting to when it dies. Or maybe a very slow leak elsewhere in the system, at a level that corresponds with the 1/4 tank draw down?

can you tell by looking if an anti siphon valve is working? I would just remove it ( temporarily ) and put a regular fitting on until this is resolved.

how about and inline pressure gauge, after the fuel pump, so you can at least confirm that the problem is lack of fuel pressure? ( as opposed to 1/4 tank of water sitting in your tank, that starts getting sucked in after the good fuel on top is used).

Gauge
 
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Sugilbert, the tank is 12 inches tall by 7 ft long. the pickup tubes go to about 2 inches off the floor of the tank and are located at the rear of the tank-I assume to keep from sucking in crap off the bottom. Each time I have "run out of gas," it has been at idle speed, so I don't believe it is sucking air and the tubes have no cracks of holes in them. Please keep the suggestions coming-something has to click.
 
Alk
I too have thought that perhaps I have 25 gallons of water in the tank-highly unlikely but still a possibility as it would make the most sense. I will order a tube of Kolor Cut just to confirm that isn't the issue. Thanks for bringing that possibility up. Bill, if it was the fuel vent, why would it only happen at the 25 gallon mark rather than at various times?
 
Ok, a way outside the box question. Is there a chance you have a piece of flexible debris floating in that tank and it only fowls your pickup when the tank is low? I know sounds crazy, but crazy might be the answer… besides all the logical answers have been given.😜
 
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are you going by the gauge that you have 25 gallons left?

reason I ask is that if the tank is 12 inches tall and tubes are 2 inches above the bottom, you've got 17 gallons of fuel that is not accessible. Gauge could be that much off
 
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If the pick up is 2” of the bottom and the tank is only 12”, that’s almost 20 gallons unusable. That s a lot.
 
Pascal, Getakey You post a very interesting possibility. I do know that the gas gauge for the port tank reads 25 gallons low from the many years of using the boat and logging hrs and fill up volumes. I assumed the pickup tube was designed to be 2 inches off the floor of the tank as both pickup tubes are the same length and I had measured the tank depth and the pickup depth. At cruise or underway, the location of the pickup tubes at the stern side of the tank, gas would be forced to the stern keeping the tubes submerged. Does anyone know if designing the pickup tube a few inches off the bottom of an inboard tank the norm? My Kolor Kut will be delivered soon so I can at least rule out the possibility of having a bunch of water in the tank.
 
I’m betting against water in the bottom of the tank. Thinking about it some more since I mentioned it earlier - if you had water down there, the pickup would always be sucking the water from the bottom, so would not run right prior to stalling out - which doesn’t seem to be the case.

i am sticking with leak somewhere in the pickup or fuel line, and the position of the leak corresponds with the level you are hitting in the tank when it dies.

long shot is problem with a failing fuel pump. If you don’t want to spend the money on an in-line pressure gauge,,my next suggestion is that next time the motor dies - remove the fuel line from the carb, place it in a jar, and crank the motor. Does the pump squirt a nice volume off fuel into the jar?

also wanted to say welcome back to posting on boatered! Looks like you took a 14 year hiatus. Glad to have you back!
 
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