Fuel Any difference between a 2 stroke and 4 stroke fuel filter?

[turbofiat124]

Hey this isn't related to lawn mowers but my Trabant 601. It's got a 2 stroke 2 cylinder air cooled engine.

James Seabolt's (turbofiat) Library | Photobucket

I wouldn't think much could go wrong with a gravity feed fuel system but boy was I wrong!

First of all I've had a rash of clogged fuel filter issues here lately. Not just with my Trabbi but my Subaru Legacy Baja and my turbocharged Yugo. Maybe just lack of maintanence I don't know.

With my Trabant, I did away with the dash mounted petcock valve and went with a solenoid operated shutoff valve connected to the coil, a conical stone media type inline filter and an inline fuel shutoff valve before both of those. It's got a 6 gallon gravity feed fuel system and a 1/4" fuel line.

I used one of those small stone type conical fuel filters from a lawnmower. Like this one:

These work great on my 49cc two stroke dirt bikes but after a few hundred miles on my Trabant, it clogged up. Under fuel throttle, I was sucking the fuel bowl dry which was leading to backfiring and such.

So I found a bigger filter from Autozone. I don't have a good photo of it but it's much larger and should have done the job. So I was coming home this morning and once again, was going up a hill and the car started running out of fuel and backfiring. This time the fuel filter was not full of crap but when I disconnected the hose after it, fuel just trickled out of it. Made sure the problem was not my solenoid valve.

Pulled a spare filter out of my toolbox, installed it and made it home.

I have no clue was to why this filter became restricted after just 50 miles despite there is very little sediment inside it. Two theories come to mind.

One is the headpressure in the tank with 6 gallons maybe enough to force fuel through it but once the tank get's down to 3 gallons, there was just not enough head pressure to force fuel through the filter. This particular filter looks like it's made of foam instead of the usual corragated cardboard material. It was one of those universal filters at Autozone. I don't think it was for a lawnmower application.

The other theory is the filter material itself. Perhaps the 2 cycle oil in the fuel blinded the filter media over and caused it to restrict flow to a trickle.

I have no idea how much headpressure 6 gallons of fuel forced through a 1/4" fuel hose would be but it's probably no more than 2 lbs if that.

So I went to O'Relieys and picked up a Mr. Gasket screen type filter like this one:

I should mention that the inside of the tank is not full of rust. This is just general garbage that comes out of the pump at the fuel station.

I've been trying to use one of those Mr. Funnels to prefilter my gas before I put it in my fuel tank. I mix up my 2 cycle fuel in 7 gallon batches then pour it in.

So the question is, why am I having so much trouble with these fuel filters?

The one with the stone filter media seems to be the least restrictive but due to the volume of fuel that has to go through it at 25 to 35 mpg, it's probably just too small for a 600cc engine. After all it's supposed to be for a lawnmower or dirt bike.

Yet another type of filter I've been using with 2 strokes is one of those made of corrogated cardboard material. I'm using one of these on my moped:

No problems so far with it but it's only 49cc and get's 100 to 150 mpg.

Does my 2 cycle oil theory sound logical with the last filter I used due to the foam filter media?

If this Mr. Gasket fuel filter does not last either, I suppose I could go with an old fashioned sediment bowl like the one on my 58 Ford 800 tractor!

 

[Rivets]

If you are sure that your gas tank is clean, I would be looking for a new place to fill the tank. The problem is not which filter to use, they are all doing their job, but the fuel going through them. I would stick to a large, clear body corrugated filter, be you can easily monitor and replace as needed.

 

[SeniorCitizen]

The elevation above the filter is what determines pressure, so yes there would be slightly less pressure with 3 gallons in the tank as opposed to 6 but pretty insignificant.

Using water as a standard, which provides 1 lb. pressure for each 28" elevation differential, you can calculate fairly accurately the pressure of gasoline if you know the specific gravity of the gas.

A sediment bowl will only be effective when the foreign matter has a specific gravity greater than the gasoline. Example: water, rust particles etc. but they are good for what they are designed for.

Mentioned earlier, change fuel suppliers.

 

[gfp55]

The elevation above the filter is what determines pressure, so yes there would be slightly less pressure with 3 gallons in the tank as opposed to 6 but pretty insignificant.

Using water as a standard, which provides 1 lb. pressure for each 28" elevation differential, you can calculate fairly accurately the pressure of gasoline if you know the specific gravity of the gas.

A sediment bowl will only be effective when the foreign matter has a specific gravity greater than the gasoline. Example: water, rust particles etc. but they are good for what they are designed for.

Mentioned earlier, change fuel suppliers.

Thank you SC, I learned something today. Good stuff!

 

[reynoldston]

I have never really used different filters in lawn equipment. But working on snowmobiles I have. I have used the paper style fuel filters on the two cycle snowmobiles for years and never had a problem with them. They use the same style fuel pump as 4 cycle lawn mower. I have found that the paper style filters do plug faster if there is a lot of rust and dirt in the fuel, but that is the filters job.

 

[Carscw]

This is what I use in all my mowers.
Just have to replace the paper filter not the whole unit.

 

[turbofiat124]

This is what I use in all my mowers.
Just have to replace the paper filter not the whole unit.

View attachment 22443

I just bought one of those and after hooking it up and turning on my fuel tap, it filled quickly so I think it will do the job.

 

[turbofiat124]

I have never really used different filters in lawn equipment. But working on snowmobiles I have. I have used the paper style fuel filters on the two cycle snowmobiles for years and never had a problem with them. They use the same style fuel pump as 4 cycle lawn mower. I have found that the paper style filters do plug faster if there is a lot of rust and dirt in the fuel, but that is the filters job.

This particluar filter I bought from Autozone looks like a foam spong material instead of corrogated cardboard like what I used on my moped. So that just lead me to think that the material itself was getting blinded over with 2 cycle oil.

But 2 cycle oil would pass through a piece of paper/cardboard.

 

[turbofiat124]

Mentioned earlier, change fuel suppliers.

Well the thing is I hate using E10 in anything with a carb. Any gas I use in my lawn equiptment and my Trabant I use 100% gas from a particular gas station in Scott County Virginia. They have above ground tanks. I don't know if that makes any difference or not but they look like they are in good shape.

I've never had any issues with E10 eating rubber parts like the diaphrams out of weedwacker carbs but rather gumming up the float valves. I've had to take apart many carbs to free up the float valve it they sit over the winter. Seems when the stuff evaporates out of the bowl, it leaves a residue behind on the float valve.

I have no idea why E10 is higher than straight gasoline since it costs more to produce ethanol and gasoline. I know it's all on account of emmisions and not foreign dependancy. It's an EPA thing since E10 burns cleaner. So I suspect the reason it costs more is due to some sort of carbon footprint tax.

That being said, pure gas is about 80 cents to a $1.00 higher here in Kingsport TN which is an industrial city. But across the state line in rural Virginia it's only 15 cents more than E10 on the Tennessee side.

I seem to think in larger industrial cities, E10 is more expensive due to a carbon tax. Where as by buying pure gas across the state line in Virginia which that county is considered rural, the carbon tax is only 10 or 15 cents.

Is there any truth to that or am I just a conspiracy theorist?

 

[Bob E]

Well the thing is I hate using E10 in anything with a carb. Any gas I use in my lawn equiptment and my Trabant I use 100% gas from a particular gas station in Scott County Virginia. They have above ground tanks. I don't know if that makes any difference or not but they look like they are in good shape.

Tell them their gas is dirty :laughing: They might clean out their tanks, add a filter or tell their supplier... In the mean time I would buy from somewhere else.

I've never had any issues with E10 eating rubber parts like the diaphrams out of weedwacker carbs but rather gumming up the float valves. I've had to take apart many carbs to free up the float valve it they sit over the winter. Seems when the stuff evaporates out of the bowl, it leaves a residue behind on the float valve.

Drain the float before letting an engine sit for long periods of time.