Ask the Editors: No Fuel But a Full Tank
Fuel system failure.
Well this question leads to a few more questions – did the machine run okay with the cap removed? If so you are experiencing vapor-lock – this is when vaporized fuel creates back pressure in the fuel system. As it prevents gas from getting to your engine, it will appear like you are out of gas regardless of how much is in your tank.
This is why most ATV gas caps are vented, to allow back pressure to release into the atmosphere rather than stop your fuel from flowing. If removing the cap cured your problem, the vented cap has probably become clogged. Replacing it should get you back in good shape.
If it makes no difference either way – time to check your fuel line from blockage for accumulated sludge. Disconnect the fuel line from the carb, turn on the petcock and see if gasoline flows freely from the hose. If it doesn’t, you have an obstruction either in the fuel line itself or at the bottom of the gas tank where it enters the line. Drain the tank and try blowing air up the line if so.
This, of course, after making sure the fuel filter itself isn’t clogged. From what you describe, it sounds like you are getting fuel as far as the filter, but none after it. If so, you have your answer.
Personally, we’re going with vapor lock on account of the fact that your tank released pressure when you removed the cap. When properly vented, the air space that becomes compressed due to the expansion of the fuel volume inside (thanks to temperature changes) is usually allowed to escape freely.
