Fuel Starvation Problem
#1
08-04-15, 07:00 AM
Fuel Starvation Problem
I have a Simplicity Landlord tractor with a Briggs Vanguard V-twin 16 HP engine with 600 hours on it. The gas tank is under the seat. There’s a vacuum-pulse fuel pump that mounts on the engine. I’ve been having a marginal fuel delivery issue. The engine starts up and runs fine for maybe 30 or 40 minutes. Then it runs out of fuel—the fuel filter empties out. If I let the tractor sit for a while then it will start right up again. If I set the engine speed to low right after it starves out and crank the engine it’s likely to draw enough fuel to get it running. If I then let it idle for a while the fuel filter tends to fill back up. If I disconnect the fuel line where it enters the fuel pump (after the filter) and lower the hose end fuel runs back into the filter.
I’ve replaced the fuel filter with an oversized Fram filter, replaced the fuel pump (that seemed to delay the onset of the problem somewhat but didn’t fix it), and replaced the very short rubber hose that connects the valve cover to the pulse port on the pump (it was distorted by heat). I’ve removed the metal fuel pick-up tube from the tank and blown through it both ways. I’ve disconnected the hoses that connect the fuel pick-up tube to the fuel filter and the fuel filter to the fuel pump and blown through them—no problem. The hoses are not dry/cracked or heat distorted. I’ve removed the fuel filler cap with the built-in gauge. The problem persists. I’ve hooked everything back up except the hose that goes into the carbs, put a length of rubber hose onto the pulse port of the fuel pump and sucked/blown through it. Plenty of gas squirts out of the fuel pump.
I’m running out of things to check or replace. I’m beginning to wonder if the fuel pump is not getting the right vacuum/pressure pulses. What could affect that? Valve clearance? What else can I check?
I’ve replaced the fuel filter with an oversized Fram filter, replaced the fuel pump (that seemed to delay the onset of the problem somewhat but didn’t fix it), and replaced the very short rubber hose that connects the valve cover to the pulse port on the pump (it was distorted by heat). I’ve removed the metal fuel pick-up tube from the tank and blown through it both ways. I’ve disconnected the hoses that connect the fuel pick-up tube to the fuel filter and the fuel filter to the fuel pump and blown through them—no problem. The hoses are not dry/cracked or heat distorted. I’ve removed the fuel filler cap with the built-in gauge. The problem persists. I’ve hooked everything back up except the hose that goes into the carbs, put a length of rubber hose onto the pulse port of the fuel pump and sucked/blown through it. Plenty of gas squirts out of the fuel pump.
I’m running out of things to check or replace. I’m beginning to wonder if the fuel pump is not getting the right vacuum/pressure pulses. What could affect that? Valve clearance? What else can I check?
#2
08-04-15, 07:15 AM
Is the replacement fuel cap vented, and are you sure that the vent isn't plugged? That's where I would start, based on everything else that you have mentioned.
#3
08-04-15, 07:57 AM
I actually didn't replace the fuel filler cap. I loosened it a turn or so and then ran the tractor that way. I still had the problem. I also checked to make sure the vent was not plugged, and it wasn't.
#4
08-04-15, 10:11 AM
Forum Topic Moderator
Have you replaced the fuel line from the tank to the pump? Even though you can blow through it, sometimes the inner lining swells and comes loose. When you blow through this, it pushes it out against the outer walls, but when the fuel pump sucks, it flaps in and closes off fuel flow.
#5
08-04-15, 10:39 AM
No, I haven't replaced those lines. I've never heard of the problem you mention, but that's why I post problems like this. These things can really be perverse, can't they? I will replace the lines and post back.
I keep forgetting to mention that this problem seems to be worse (happens sooner) when it's really hot out or I'm mowing heavy grass in the field next to our house. I've run the tractor with the hood open to watch the gas in the fuel filter and have been surprised by the volume of really hot air coming from the engine compartment. Does that suggest anything else?
I keep forgetting to mention that this problem seems to be worse (happens sooner) when it's really hot out or I'm mowing heavy grass in the field next to our house. I've run the tractor with the hood open to watch the gas in the fuel filter and have been surprised by the volume of really hot air coming from the engine compartment. Does that suggest anything else?
#6
08-04-15, 11:32 PM
Forum Topic Moderator
The heat is pretty normal, it's an air cooled engine and they can get pretty hot. The heat makes the rubber hoses softer too, so that makes sense.
#7
08-06-15, 05:44 PM
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Fuel lines might be weak on the inside and flapping to stop flow. Or you might have a screen, fiter in the tank. I had a radiator hose on my truck that stopped the flow of water the same way.
#8
08-07-15, 06:24 AM
New Fuel Lines
OK, so I replaced the fuel lines that run from the tank to the filter and from the filter to the fuel pump. Those are the lines under suction. With those lines and filter completely empty, I started up the engine. It took maybe 15-20 seconds for fuel to appear in the filter. Then the filter went to two thirds full in maybe another ten seconds. This is an oversized filter, 1.5 inches in diameter and almost two inches long. So the system was really moving the fuel.
I cut our lawn and part of the field next door and the tractor ran without a hitch. But when I checked the filter during and after cutting it was nearly empty, same as before. What causes this to happen? Heat from the engine causing the fuel vapors and air in the filter to expand? Leftover hot air from last night's Rep presidential debate? How full should the filter be?
The only caveat I have to add is that yesterday was pleasantly warm (upper 70's). The final exam will come on a hot day. But I'd have to say things are definitely looking up. Thanks!
I cut our lawn and part of the field next door and the tractor ran without a hitch. But when I checked the filter during and after cutting it was nearly empty, same as before. What causes this to happen? Heat from the engine causing the fuel vapors and air in the filter to expand? Leftover hot air from last night's Rep presidential debate? How full should the filter be?
The only caveat I have to add is that yesterday was pleasantly warm (upper 70's). The final exam will come on a hot day. But I'd have to say things are definitely looking up. Thanks!
#9
08-07-15, 10:20 AM
Forum Topic Moderator
It's normal for there to be air in the filter. Sometimes the fuel will only be at the very bottom of it. It doesn't really indicate anything unless the filter is empty.
Last edited by cheese; 08-08-15 at 10:02 AM.
#10
08-07-15, 12:44 PM
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Valve cover
Is your valve cover leaking oil ? The one the fuel pump hose goes into. it might be sucking air or may have a filter screen inside the cover that's clogged.
What's your model and type # on the engine.
What's your model and type # on the engine.
#11
08-08-15, 05:54 AM
No oil leak from the valve cover. No filter screen inside the cover. Brass nipple that threads into the valve cover is free and clear. Model # 303777, type 1111-A1. At this point I think it's likely the new suction hoses did the trick.
#12
08-19-15, 05:56 PM
OK, hot day today. I mowed the entire lawn and the tractor ran fine. When I check the fuel filter after mowing it has just a little bit of gas in the bottom. I don't understand that but as long as the tractor works fine I'm not going to worry about it. Thanks again.
