Fuel Cap Vent Filter

canuck1969

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Had to disassemble my fuel cap vent assembly to clean it out as it was plugged (84 Special). There was the remnants of a foam filter onto of the disk washer. How critical is that to the operation or is it just to keep crap out of the air. Seems counter intuitive as it will trap any dirt. Seems to run fine and vent without it.

I have some Uni filter material I can use but is it worth taking apart again to replace it.
 
It is mentioned in post #3 of this thread. They seem to imply it is required, but yours seems to be working fine without it .....

http://www.xs650.com/threads/gas-cap-seal-replacement-how-to.30058/#post-585672

If you do has issues down the road, a substitute (Scotchbrite pad) is mentioned.

I saw that post before and didn't follow the logic after looking at the small disk but then it dawned on me on why the filter is important.

Without the filter material the small metal vent disk will be able to move up in down in the vent. At first not a big issue but then realized that when the disk is in the down position (ie tank cap closed) it covers the offset hole in the fibre disk. Fine for pressure buildup in the tank but when fuel is drawn from the tank the disk will rest on the fibre vent seal and plug the vent hole. The vibration of the motor keeps the disk bouncing around in the cavity so seems like it is a non issue until the metal vent disk decides to stick to the fibre seal disk for some reason (varnish??). Then your venting is gone. Assuming they put the offset hole to act as a labyrinth seal for the fuel so it does not come out when riding with a full tank.

I used some Uni air filter foam I had lying around. Seems to be what was in there to begin with as it was highly compressible. I guess scotchbrite would work also but frankly banned that stuff in my shop. Has a habit of stick to things (like my microfibre cloths) and then reeking havoc when I go to use them to polish something. And we all know how much I like to polish things.....:love:

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The UNI material seems like a reasonable substitute Canuck.

I suppose more of us should check that little vent cap filter in our own bikes based on your experience.

Pete
 
The UNI material seems like a reasonable substitute Canuck.

I suppose more of us should check that little vent cap filter in our own bikes based on your experience.

Pete

Yup....

To have it all in one thread, here is what it looked like before.

The metal disk is below the foam filter. Really anything in there has nowhere to go so I can see why they build up over time. The filter will just hold it all in. Add old fuel to the mix and it is just a sticky mess. Best scenario is to just remove the filter and metal disk and drill a bigger hole in the fibre disk for full venting but then you will have fuel slosh out on a full tank.

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