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fuel problem

O

oil driver

Contributing Member
While running close to wot the fuel bulb collapsed. I was unable to get a firm bulb, but I was able to restart and run slow. I disconnected the line from the tank to the water separator, and I blew back the line after which The fuel flowed. I cleaned the separator and replaced the cannister. The fuel bulb is fairly new so I reconnected and started the engine. The bulb was pretty firm, so I was about to take a test run and the engine stalled. Again I was unable to pump the bulb hard. Aside from changing the fuel lines and bulb, is there something else to look for? I don't see any leaks. though I haven't looked thoroughly.
 
I'm assuming this is an on board fuel tank. If it is... there is a check valve at the outlet of the tank. It may be clogged. Or you have a faulty vent. The check valve only let's the fuel travel out. So you never lose initial prime.
 
Was it the first run of the year? If so, could be a screen in the fuel tank at the bottom of the pickup tube. Do you always use non-oxy fuel? Or do you get ethanol? Ethanol suspends water and separates, becoming heavier and sinks to the bottom of the tank. BINGO! With it goes much of your octane too. This creates a dangerous combination of compounds which can give you a world of problems. Additives can do little but help delay some deterioration and fuel separation and in some cases dissolve accumulated deposits.
My personal equipment runs beautiful from year to year and season to season on non-oxy, and the ethanol is reserved for daily use in the family car and truck.
 
Last edited:
mechanicman said:
I'm assuming this is an on board fuel tank. If it is... there is a check valve at the outlet of the tank. It may be clogged. Or you have a faulty vent. The check valve only let's the fuel travel out. So you never lose initial prime.
Click to expand...

I blew back the line pretty hard and I got fuel to flow. If I blew the check valve too hard and damaged the check valvewould that have made my problem worse?
 
oil driver said:
I blew back the line pretty hard and I got fuel to flow. If I blew the check valve too hard and damaged the check valve would that have made my problem worse?
Click to expand...

That indicates a "Anti Siphon" valve problem (below).

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(Fuel Anti Siphon Valve)
(J. Reeves)

Many of the later OMC V/6 engines incorporate a fuel restriction warning via a vacuum device attached to the powerhead. If the engine overheats, or if you have a fuel restriction, the warning is the same.... a steady constant beep.

NOTE... Only the V/6 & V/8 engines have the above "Fuel Restriction Warning". The warning horn will not sound on the other models.

The fact that a engine is not overheating, but the warning horn sounds off with a constant steady beep, and that the rpms drop drastically would indicate that the engine is starving for fuel due to a fuel restriction. Check the built in fuel tank where the rubber fuel line attaches to the tank fitting. That fitting is in all probability a "Anti Siphon" valve which is notorious for sticking in a semi closed position. It will be aluminum, about 2" long, and the insides of it will consist of a spring, a ball, and a ball seat. If this valve exists, remove it, knock out those inner components which will convert it to a straight through fitting, then re-install it. Hopefully that cures the problem.

The above procedure will cure a restriction problem with the anti siphon valve as stated. BUT, it may also allow fuel to drain backwards to the fuel tank when the engine is not running (siphoning backwards) due to the fact that the carburetors/fuel pump etc are higher than the fuel tank. This condition is not an absolute as the valves in the fuel primer bulb usually prevent this backwards siphoning problem. However.... if this does take place, the cure would be to install a new anti siphon valve.

NOTE: There has been cases when the output valve in the fuel primer bulb would come apart, and the inner portion of the valve would actually reverse itself and be drawn back into the primer bulb's output valve body. This in effect would create a shut off valve and result in a fuel restriction. If this is the case, you should be able to feel something laying in the bottom of the primer bulb when held horizontally.

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Excellent information, Joe. The fuel pump is trying so hard to pull fuel that the primer bulb is going flat. The restriction has to be in that check valve. If "Driver" blew back to hard, it could be damaged. But some debris is dislodged off the pickup screen, (if it has one)....enough to allow better flow, depending on the check valves condition.
 
Could be the air vent in your tank cap is partially blocked.You could try running with the cap off.If it runs ok,it's a blockage in the vent.
 
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