Water in fuel

by Had Robinson
updated July 31, 2019

This spring (2019) has been one of the wettest on record for many parts of the U.S. and Europe.  As a result, gasoline contaminated with water has become a common problem for all users of gasoline.  Automobiles generally use ethanol blends of fuel.  These blends absorb the water (if not too much) and modern fuel injected engines do not mind.

Water is the single most destructive contaminant in a fuel system." Howard Chesneau Fuel Quality Services, Inc.

It is quite another matter with paramotors, especially if they use ethanol-free fuels.  The water will sink to the bottom of the tank and get in the system.  When this happens, the fuel pump will work intermittently, if at all.  The engine will be hard to start or suddenly quit.

Here is a photo of a Walbro WG-8 fuel pump diaphragm covered with water.  The inlet filter screen of the pump was also full of water and ruined and had to be replaced.  This motor would neither start nor run.  If your motor is running well otherwise, suddenly quits or will not start, and the weather has been wet, take off the carburetor fuel pump cover plate and take a look.  The inline fuel filter will probably have water in it, too.

water contaminated fuel pump in a paramotor

Walbro WG-8 inlet filter screen contaminated by water and debris

If you do have water in the system, you will have to remove and disassemble the carburetor and let it dry out.  (See the carburetor rebuild page for help.)

Handy pilots can carefully siphon or pour the good fuel out of the tank and leave the watery gunk behind which can be disposed of.

The fuel system must be purged.  The inline fuel filter should be replaced as water may have damaged it.  Remove the current filter but do not replace it until you have completed the steps below.

  1. Remove the tank from the frame.
  2. The "clunk" in the bottom of the tank should be carefully examined for water and gunk.
  3. Rinse the "clunk" in rubbing alcohol and let it dry.
  4. Pour a few ounces of rubbing alcohol in the tank and shake the tank vigorously.
  5. Pour out the alcohol and let the tank dry out.  Compressed air can help it dry quickly.
  6. Use compressed air to blow all lines IN THE REVERSE DIRECTION of normal fuel flow.  The "clunk" can remain on the pickup tube.
  7. Let everything dry out for a few hours.
  8. Reassemble everything, put in the new inline fuel filter, but DO NOT connect the fuel line to the carburetor.
  9. Put fresh fuel and oil in the tank and prime the fuel system with the primer tube or the squeeze bulb.  Make sure you can easily get fuel out of the line that goes to the carburetor.  Pump about a cup (250ml) or so of fuel through the system.
  10. Examine the fuel that came out for the presence of debris or water.  If there is anything, repeat the purge process.  The fuel going into the carburetor must be absolutely clean and free of all contaminants.

Once things are in order, reconnect the fuel to the carburetor, prime the system, and attempt to start the engine.  Things should be good to go.  Remember that filters are easily clogged by water and must be replaced.  The exception is the "clunk" filter.

Turkey Vulture