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

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



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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!