Simple fuel filter question

Hi guys, I have a simple fuel line filter question. I just bought a lawnmower fuel line filter and installed it in my moped. Some filters are made for different horsepower engines (this Briggs filter did not specifiy any horsepower requirement so I picked it up thinking it would be fine although it looks a little big). I was wondering if it really matters whether I got a lawnmower fuel line filter or motorcycle filter and if I need a specific fuel line filter. The moped (1977 columbia commuter sachs moped) runs but doesn't do well in idle (I don't think it did well before the filter was installed either but I was just checking to see if the filter could make a difference) . I don't know if the filter could be causing this and if I should get a motorcycle filter. Also, the filter is inclined at 45 degrees for spacing reasons and I didn't know if this was a problem or made it difficult to pump the fuel up. I appreciate any help. Thanks.

Re: Simple fuel filter question

Hey guys, just looked up my fuel filter online and the specifics said that it was 30 microns, which is small (I saw on this forum that 80 microns is the recommended minimum). I was wondering if this was the reason for the problems in idle? I am planning on changing the filter anyways but I would just like to know. Thanks alot.

Re: Simple fuel filter question

A fuel filter either allows enough fuel to pass through or it doesn't. Idling requires very little fuel.. chances are that a tiny, clogged filter would still allow a bike to idle. If the carb's float bowl is full of fuel the bike may idle for many minutes even if fuel is shut off completely.

These carbs are gravity-feed (there is no fuel pump). Weird siphoning trouble might be set up somehow in a fuel line but, off the top of my head i can't imagine how . I'd be more concerned with placing a plastic filter too close to the engine's high heat.

I'm not a fan of add-on filters of any kind and prefer to repair and use what came on the bike originally. Additional filters do nothing that original equipment doesn't do (except supply a couple more potential places for leaks to develop as well as a add a questionable-dirty-filter-should-I-throw-it-away situation)

Idle requires an abnormally rich air:fuel mixture .. So, a carb has a separate, internal idling system that usually requires adjustment to get the idle correct. When adjusting idle speed and/or mixture, the engine must be warmed up first or it won't idle when it's hot. Exacctly what can and can't be done when adjusting idle depends on the carb.. some have air:fuel mixture screws and some only have idle speed screws .. I'm not familiar with your bike so i dunno.

I'd first make sure the carb was internally clean, float level adjusted, throttle and choke cables adjusted and that there are no air or fuel leaks anywhere between the air intake box and the engine.. Then set the idle speed on the warm bike. If it still idles erratically, perhaps you can also tune the idle air:fuel mixture with an external screw adjustment.

Re: Simple fuel filter question

I don't think your filter will make a difference with your idle problem, so the problem is elsewhere. As Joew states, fuel either goes through or it doesn't. Ensure you get a filter that has some gauze-like material vs a simple fine mesh. Stuff gets through the mesh that can clog up your carb. If your tank is higher than your carb, fuel will flow through your filter and into your carb bowl.

Re: Simple fuel filter question

The angle of the filter installation oes not make any difference as long as the tank is above the carb.

Re: Simple fuel filter question

be sure you got the filter facing the right way...the fuel flows DOWN to the carb, not up.


Re: Simple fuel filter question

Yeah, it is installed correctly, I think I will try and take some of the suggestions you guys mentioned and work on it this weekend. I think it will be okay, I will get a new filter first because the one I have is too small, it is only 30 microns, and then I will try and clean out the carb. I'll see if it helps, thanks alot though. If you have any other suggestions let me know. Thanks.

Re: Simple fuel filter question

As for buying a fancy pants fuel filter, I went to a local Canadian Tire auto section and looked for a small filter, transparent/translucent (so I could see if there's fuel in it), one that fit the space I had, and cheap ($8CAD). Some fuel filters have different angles and come with different input/output diameter pipes. Some are all metal to resist heat. I bought a plastic one.

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