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Fuel Filters

by Had Robinson

If the best is desired, we stock a 10 micron inline fuel filter used in commercial chain saws for $6, free shipping to the U.S.  It is the same size as the commonly used OEM filters.  Contact us via email to order.  The original OEM filter is also available from Miniplane-USA.  Do NOT use the inline fuel filters sold in auto parts stores.  They are of inferior quality and will not block the small particles that clog the inlet filter screen in the carburetor.

Filter quality & capacity

Why bother with a high quality filter?  In two stroke engines, the fuel filter is also the engine oil filter.  It must be able to trap all of the grit and other contaminants in the fuel and lubricating oil.  This will prevent the carburetor from getting clogged, especially the pump inlet fuel filter screen.  A clogged carburetor will lean out the fuel mixture and can burn up the engine.  The lubricating oil also needs to be filtered in order to prevent premature wear of engine parts.


Aviation engine forums (ROTAX) note that paper filters are the best because they have the finest filtration media – around 10 microns vs. 40+ micros for sintered bronze or the pickup tube filters sitting at the bottom of fuel tanks.  The non-paper filters do not trap the very small particles which will clog the pump inlet fuel filter screen and other tiny openings in the carburetor.  A clear filter housing must be used because pilots need to be able to periodically check that the filter is not clogged or damaged.

Here is a clogged pump inlet fuel filter screen from a Walbro carburetor.  Instead of using a quality filter, the pilot used a sintered bronze filter which allowed contaminants to reach the carburetor.  This engine experienced fuel starvation and overheated.  Fortunately, it was not damaged because the lack of fuel was so severe the engine shut down before major damage could occur.  Some paramotors do not even come with a fuel filter!

fuel inlet filter clogged with debris

Here is a sintered bronze filter.  The dirt-bike guys derisively refer to these as "lawnmower filters" because of their inability to filter well.  The media is just not fine enough to stop small particles from passing through.  These work satisfactorily in 4 cycle lawnmower engines, more or less, but in nothing else.

sintered bronze fuel filter 

Fuel pump diaphragm showing signs of water contamination in the fuel, probably from using ethanol blends.

WG-8 fuel pump diaphragm with water contamination

Below is a photo of the WIX #33001 inline fuel filter (L) and a similar filter (R) sold by the auto parts stores.  The WIX can be used in all paramotors, if you can find it.  The only problem with the WIX is that it is about twice the size of the OEM filters and may take a bit more thought as to where to put it.  The filter we supply is the same size as most OEM's but of better quality and is a nominal 10 microns.  Note that the size of the WIX filtering media is probably 20X that of the other.  The filter media of the WIX is a nominal 12 microns.  Who knows what it is of the filter on the right?

Most inline filters are rated at 40 or more microns which is not enough to keep the pump inlet fuel filter screen from clogging up.  The absence of barbs on the hose connections guarantees that the filter on the right will leak or come loose at some point – which could be hazardous.  Why put a cheap fuel filter on a $2,000 engine?

WIX fuel filter and a poor quality inline fuel filter

Depending on use, fuel filters should be replaced yearly.  Ethanol fuel blends and fuel that is contaminated by water hasten the deterioration of paper fuel filters.

The in-tank filter on the end of the fuel pickup hose should always be checked regularly to be sure it is not clogged.  This can be easily done by removing the fuel line to the carburetor and pressurizing the fuel tank using the priming tube with a hefty breath or the primer bulb, if your engine has one.  Fuel should come easily out of the tube.  There should be no restrictions on the fuel movement.  This quick test will also assure you that the fuel system from the tank is in good order.

Ethanol fuel blends can form gelatinous globs from contaminants which will quickly clog the fuel pickup tube filter in the tank.  Be sure to check it often using the quick fuel system test or the test above.

Installation tips

To easily remove the fuel filter from the tubing, heat the tubing with a hot air gun or a hair dryer until it is almost too hot to touch.  The tubing will easily slip right off of the fittings without damaging anything.

When connecting the filter, put a small amount of 100% silicone grease (Vaseline can used but it is not as good) on the outlets and inside the tubing.  This will greatly ease the installation of the tubing.  It will also help keep it from splitting.  Silicone grease is always the best for fuel fittings and tubing because it is 100% inert and is not soluble in any liquid.  It also will not oxidize over time.  The downside of it is that it is expensive.

If the WIX filter is used, its large size has to be considered.  The best location is just to the outside of the upper engine mount, between it and air box.  It fits in here nicely.  The downside is that the fuel line tubing will have to be longer.  If the WIX is placed in the same location as the OEM filter, it may be tight and will rub on things.  Keep an eye on it to sure the filter is not damaged enough to leak air.

WIX fuel filter location on the Top 80 paramator