Why the fuel valve is important on small gas engines

dreamstime_49730376Protect your engine, turn off your fuel

You just finished a job using your gas drive air compressor and you’re getting ready to drive to your next job. Did you remember to shut off your fuel valve?  In this article we’ll explain why you should.

Most small gas engines have a fuel valve that should be shut off by when the engine is not in use.  This can be easy to forget, especially when using remote controls.

Fuel shut-off becomes important when moving equipment as vibration can cause the carburetor needle valve to move allowing fuel to trickle into the carburetor, the float chamber and down the intake valve.  This can cause:

  1. Engine flood, causing downtime waiting for the flood to clear.
  2. Dilution, when fuel goes past piston rings and mixes with oil, causing engine damage.
  3. Hydraulic lock, when incompressible liquid causes engine damage or failure.

Best practice for small gas engines – ensure equipment is on level ground, and the fuel valve is shut off when re-fueling and when equipment is not in use.

Why does the engine flood?

Any time vibration causes the carburetor float to drop in the float chamber, pressure is reduced against the needle valve.  Reduced pressure against the needle valve allows pressurized fuel from the fuel tank to pass through the valve.

If this happens frequently, fuel will overfill the float chamber, flood down the throat of the carburetor, and flow into the cylinder through the open intake valve.

Fuel in the cylinder can flood the combustion chamber above the piston, creating hydraulic lock, preventing the engine from turning. This fuel will also slowly drain past the piston rings, diluting the oil in the crank case. If the engine manages to start with diluted oil, severe and premature engine damage will follow.

How does the float work?

The float chamber is located below the carburetor body. Through the operation of the float and the needle valve, the float chamber maintains a constant fuel level while the engine is working. The fuel flows from the tank into the float chamber through the needle valve. When the fuel rises to a specific level, the float rises. When the buoyancy of the float is balanced with the fuel pressure, the needle valve shuts off the fuel passage, thereby maintaining the fuel at the predetermined level.

Any other reasons?

Not only does shutting off the fuel valve prevent the engine from flooding while being transported, it prevents flooding because of contamination in the float valve, and extends the life of the float valve by decreasing pressure on it.

Is this unique to Subaru engines?

Most manufacturers of small gas engines have this same issue.  Like the Subaru engines used in VMAC G30 Gas Drive Air Compressors, Honda and Kohler engines used in other air compressor brands state in their literature that fuel valves should be shut off when not in use, including during transport.

VMAC G30 Gas Drive Air Compressors are powered by Subaru’s 14HP EX40 OHC Engine.  The G30 is a Subaru-approved application.  The engine includes electric start capability, is EPA and CARB-compliant, and comes with an industry leading 5-year warranty.

Do you have questions about VMAC’s G30 Gas Drive Air Compressor?  Please give us a call at 1-877-912-6605 or email us at sales@vmacair.com.

For more information, you can also visit the VMAC G30 Gas Drive website.

To view all articles posted please visit the Gas Drive Education Series main page.