Gravity fuel filter test

[Old Rider]

I have read some reports that gravity feed bikes don't like a inline fuelfilter that can lead to fuel starvation but i did a test with taking the inner brass material out of a filterhousing and stuffed it 3 centimeters innside a fuelhose and clamped it with hoseclamp  .I tested the fuelflow and it flows very easy so i think i will try this. Anyone tested this before ??

[FJmonkey]

A fresh filter will flow better than one with some service on it. The issue of starvation is a factor of how clogged the filter is, the amount of fuel in the tank pushing it down and the amount your right hand/wrist is twisting the throttle.  The ability to remove the filter in the field should be considered to avoid limping home slowly when the filter is clogged.

[red]

I have read some reports that gravity feed bikes don't like a inline fuelfilter that can lead to fuel starvation but i did a test with taking the inner brass material out of a filterhousing and stuffed it 3 centimeters innside a fuelhose and clamped it with hoseclamp  .I tested the fuelflow and it flows very easy so i think i will try this. Anyone tested this before ?

Old Rider,

I don't doubt that a new filter element, even paper, will flow nicely.  After some use, though, it may get somewhat clogged, especially with only gravity feed to push fuel through it.  OTOH, I do have doubts about the wisdom of putting any filter element inside a black hose, though.  I would want to see if/when the filter element is getting dirty.  To that end, I would want a filter that has a water-clear glass enclosure, and the inlet fuel on the outside of the filter element.  Since the fuel flow is only gravity-powered, I could also see using a Y-pipe in the fuel line and running two such filters in parallel, so to double the area of the filtering element(s).  The glass filters may have a nylon or metal screen as the filter element, making them resistant to clogging and both cleanable or rebuild-able.  HTH.

https://www.sfxperformance.com/parts/SPT2369.htm
.

[Pat Conlon]

Be sure to do the time/volume comparison with low head pressure (less than 1/4 tank)
I think you'll be ok, but who knows?
Not sure that brass screen is going to pick up any debris that the petcock screen won't already trap.

We know paper filters are a no go....

[Old Rider]

A fresh filter will flow better than one with some service on it. The issue of starvation is a factor of how clogged the filter is, the amount of fuel in the tank pushing it down and the amount your right hand/wrist is twisting the throttle.  The ability to remove the filter in the field should be considered to avoid limping home slowly when the filter is clogged.

Good point!
To remove the filter in the field i  will have to loosen the hoseclamp and carry extra filter with me or just have a pre-made hose with a filter in i my luggage.

[Old Rider]

I don't doubt that a new filter element, even paper, will flow nicely.  After some use, though, it may get somewhat clogged, especially with only gravity feed to push fuel through it.  OTOH, I do have doubts about the wisdom of putting any filter element inside a black hose, though.  I would want to see if/when the filter element is getting dirty.  To that end, I would want a filter that has a water-clear glass enclosure, and the inlet fuel on the outside of the filter element.  Since the fuel flow is only gravity-powered, I could also see using a Y-pipe in the fuel line and running two such filters in parallel, so to double the area of the filtering element(s).  The glass filters may have a nylon or metal screen as the filter element, making them resistant to clogging and both cleanable or rebuild-able.  HTH.

https://www.sfxperformance.com/parts/SPT2369.htm
.

Thanks for the link to the filter it looks great but i think there might be problems because of the size 3.25" not sure where on the line to fit it without kinking the hose or breaking it when tank is mounted.
I have been thinking of using 2 brass filter inserts in the 2 hoses going from the Y pipe but that will make it difficult to remove the filters in the field.
And maybe 2 filters will double the restriction of fuel flow.

[Old Rider]

Be sure to do the time/volume comparison with low head pressure (less than 1/4 tank)
I think you'll be ok, but who knows?
Not sure that brass screen is going to pick up any debris that the petcock screen won't already trap.

We know paper filters are a no go....

So far i have just compared the flow by pouring half a litre painters alcohol thru the test hose and into a bowl and compared with and without filter placed in the hose and there is very little difference in time .The filter innside the tank is okay .The reason i want another filter is that when i put the bike away for the winter i drained the fuel by attaching a long fuelhose on the petcock and putting vacuum on the vacuumhose. when the gastank was almost empty i drained into a couple of clear pepsimax bottles.Then i discovered some particles in the drained fuel it looked like sugar or clear pearls  and formed in the bottom of the plastic bottle the amount was about 1 tea spoon.
I then drained the carb bowls (I have small fuelhoses attached on the drainscrews on the carbbowls) drained those into a half litre pepsimax bottle.
There was not much particles in that fuel but a little so the fuelscreen inside the tank is filtering out most of the particles.
i have now pulled the carbs  and  they looked clean innside .I did clean the carbs anyway.
I wonder if the small particles is some kind of fueladditive and nothing to worry about.??

I forgot to mention that the fuel hose and brass insert on the pics is not the one I'm going to use i will use 9,5mm hose and try to find a brassinsert that has bigger diameter.

[red]

Since the fuel flow is only gravity-powered, I could also see using a Y-pipe in the fuel line and running two such filters in parallel, so to double the area of the filtering element(s).  The glass filters may have a nylon or metal screen as the filter element, making them resistant to clogging and both cleanable or rebuild-able.  HTH.
https://www.sfxperformance.com/parts/SPT2369.htm

Thanks for the link to the filter it looks great but i think there might be problems because of the size 3.25" not sure where on the line to fit it without kinking the hose or breaking it when tank is mounted.  I have been thinking of using 2 brass filter inserts in the 2 hoses going from the Y pipe but that will make it difficult to remove the filters in the field.
And maybe 2 filters will double the restriction of fuel flow.

Old Rider,

The link I gave was only an illustration of my idea, not a final answer.  I'm sure that you can find "similar" units that will fit the bill.

Generally, more filter area will mean less flow restriction, especially over time.  The small metal filter element inside a hose would have a very small filter area, and it will become clogged much sooner as a result.  The glass-body fuel filters will be easy to inspect, and even if you get some minor clogging, mechanical tapping on those filters may get you enough fuel flow to make it home, without a field repair.

The best answer for use of a fuel filter is to use an add-on fuel pump with it.  Minor carb changes would be needed then, but no serious rework.  RPM can give you good advice on adding a fuel pump and fuel filter to the gravity-fed FJs.
.

[Old Rider]

And now i found this filter on a FJ https://www.youtube.com/watch?v=0VvnXuv16Yk

Today i drove to a shop that have fuel hoses in SAE 30J R9   i wanted to buy 1 meter and replace the fuel lines that was until i heard the price
70 USD !!!

Instead i bought 1 meter of R7 hose that i have used before. I wanted the R9 quality because i read it is stiffer and can hold up to ethanol better
not sure if the R9 is needed  the R7  i have used now for a year seems okay.

[mr blackstock]

Gday,
I discussed this sort of thing a few years back, even videoing a test:
https://m.youtube.com/watch?v=0VvnXuv16Yk

I found that a filter in no way restricts fuel flow.  However, if you are talking huge flows, several litres a minute, then yeah, a filter will restrict, for most riders though, I would be amazed if a rider suffered fuel starvation from a filter... Poorly placed fuel line? That could starve an engine.  I've been riding 30 years, my bikes only broke down from poor maintenance.

I know a guy who races old superbikes, always uses filters, flat track racing, still uses filters.

Just my thoughts...

Gareth

[Old Rider]

Gday,
I discussed this sort of thing a few years back, even videoing a test:
https://m.youtube.com/watch?v=0VvnXuv16Yk

I found that a filter in no way restricts fuel flow.  However, if you are talking huge flows, several litres a minute, then yeah, a filter will restrict, for most riders though, I would be amazed if a rider suffered fuel starvation from a filter... Poorly placed fuel line? That could starve an engine.  I've been riding 30 years, my bikes only broke down from poor maintenance.

I know a guy who races old superbikes, always uses filters, flat track racing, still uses filters.

Just my thoughts...

Gareth

Hi Gareth i knew i had seen that nick name before here on the forum  its good to know it works so i will try to find that inline filter.

[mr blackstock]

G'day,

Bear in mind that I had to search a few bike shops to get the slimist in-line filter I could find.  The usual plastic ones are so fat that it can crimp your fuel line in the tight space afforded by the dent in the top of the airbox.  I found one in a race shop, same diameter as the fuel hose..

Good luck, Gareth

[Old Rider]

Update: Mars 2021
Here is my latest test making a gravity inline fuelfilter . i decided not too use the filter pictured in start of this tread because it was so small .so i have found another type of insert that is larger and fits snug into a 10 millimeter hose.
since it has to be inserted about 30 millimeter into the hose because of the petcook tap it is difficult to pull it out for cleaning ,but made a steelwire run thru it so i can
grab the wire and pull it out.
I don't think this filter has so good filtration as a paper based filter, but it will be  better than no filter.On the gravity feed system i don't think its possible to use
any type of paperbased filter anyway.Yesterday was my first ride after the winter and i filled the gastank with only 4 litre of gas so the fuelpressure is low and took off.
Had no signs of fuelstarvation. The trip lasted only for about 20 miles because of cold weather only 2 degree Celsius,but that is enough to test if it was any problems.
Also i got to see how the new carburetor diaphragm worked and it was no problems with them. Bike was quick and had no hesitation or uneven /jerkiness drag when accelerating
i will update on the diaphragm later in that post

[Old Rider]

Here is the reason i want to add a extra fuel filter. I discovered that the tank liner i put in there 3 or 4 years ago has started to crack up in small pieces here and there  . maybe it can not stand up to the heat from engine since it is only in the bottom of tank.It was fine for a long time but now its crackling a little.The Liner  i used was Bill Hirsh gastank liner special for motorcycles.
It was a 3 step system with first a wash and rust remover then a etch primer  and then the white liner.It says it will withstand ethanol based fuel.
Maybe the heat form engine is the problem and it starts cracking up after some years.
When i drained the tank before winter there was only a few  small pieces in the fuel so i will ride at least one more season before doing anything
I will have to re line the tank but not sure how i will get the old liner out ?

[Motofun]

Methyl Ethyl Keytone should do the trick.  It is NASTY stuff.  Use it outdoors, wear gloves and a paint respirator.
PS...protect the exterior paint.