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How to make a vented gas cap?

Discussion in 'Chainsaw' started by Snap, Nov 15, 2019.

  1. Snap

    Snap ArboristSite Operative

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    Having trouble with fuel tank venting on a 335xpt and need a vented gas cap. A little while ago the original tank vent was changed but either something with it went wrong or it's not adequate because I am getting a stall out part way through each tank of gas. If I open the filler cap for a moment then the issue is solved for a while.

    I haven't found a fuel resistant sealant to fit a vent in the filler cap so my attempts have resulted with weeping fuel.

    Any suggestions would be appreciated.
     
  2. buttercup

    buttercup Gone fishing

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    https://www.aliexpress.com/item/328...chweb0_0,searchweb201602_1,searchweb201603_52
    https://www.aliexpress.com/item/400...chweb0_0,searchweb201602_1,searchweb201603_52
    https://www.aliexpress.com/item/329...chweb0_0,searchweb201602_1,searchweb201603_52
    These might be a little big but I guess drilling a hole in the tank cap that's just a little tight and inserting something similar would be an easy (perhaps not pretty) fix. It might be possible to have the valve on the inside so that it don't get in the way.
    Some kind of filter to catch all the saw dust might be a good idea too...

    Another kind of vent valve fix that might be more relevant to your problem is to use a piece of gas resistant hose/tube with a machine screw in the end of it, the threads of the screw will only allow a very small passage so fuel spill/leakage would be virtually none.
    So when your saw is upright the tank can breath - in or out, when you tilt the saw it is usually running so there will be a negative pressure in the tank and therefore no leakage.
    With a cone head screw you can even adjust the vent capacity somewhat by adjusting the screw in or out, or use a longer or shorter screw.

    RIMG0067.JPG
     
  3. Allen K

    Allen K Chainsaw Addict

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    scottr likes this.
  4. mkinslow

    mkinslow ArboristSite Guru

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    If its running part of the way through a tank of fuel I'd say check some other things, my experience with tank vent issues happens pretty fast,and if you're leaving the cap open for more than a second or two before it'll start back something else is going on in my opinion

    Sent from my SM-G892A using Tapatalk
     
  5. Snap

    Snap ArboristSite Operative

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    I'll look into it. The sealing has always been my problem with the vent creation.
    I also saw a reference to MotoSeal.
    Many things I found say "fule resistant" not fuel proof and the reps say they are not intented for constant wetting.
     
  6. Snap

    Snap ArboristSite Operative

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    Like what?
    I suspect the venting because before it dies it get really lean and won't idle down.
     
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  7. irhunter

    irhunter ArboristSite Operative

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    Maybe, pressure check the fuel line.
     
  8. mkinslow

    mkinslow ArboristSite Guru

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    Fuel line or an airleak opening up after it gets hot

    Sent from my SM-G892A using Tapatalk
     
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  9. hotshot

    hotshot ArboristSite Operative

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    Just saw a workaround thread in the Poulan stickies section, where he drilled a hole in the cap on a S25DA saw, inserted & glued in a short ink pen tube section, then placed a duckbill valve on the end, #530026119.

    Problem solved!
     
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  10. irhunter

    irhunter ArboristSite Operative

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    Couldn't hurt to try that. But, I am with mikinslow.
     
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  11. TRTermite

    TRTermite ArboristSite Guru

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    Fuel line collapsing This duckbill concept may work for me on other saws I am going to gander over there to look for that thread/post.
     
  12. old guy

    old guy Addicted to ArboristSite

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    I solved that problem with that very saw by drilling a hole in the cap & installing a rubber duckbill in it.
    The hole ended up the same size as the duckbill:mad: but it has not leaked or fallen out, try to get a snug fit.
     
  13. Snap

    Snap ArboristSite Operative

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    No sealant?
    I tried a bare duckbill last season and got a dribble on the bench. I don't know if there are different sized duckbills but mine was a tiny little thing and, by appearances, didn't seem capable of passing much air.

    I think the saw is a beast when it runs but that is getting less and less. Never buy a first generation of anything and this has been around here since 1997. We got our $390 worth out of it but will give it one more reprieve.
     
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  14. old guy

    old guy Addicted to ArboristSite

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    Yeah, mine is a good running little saw, but if it sits for a long time, (weeks, months,) I pull the cover and air filter off & put a little fuel in the carb to get it started, otherwise many many pulls to get it started. (yes the choke works).
     
  15. kevin j

    kevin j Addicted to ArboristSite

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    if you use the grub screw like older saws did, don’t screw it into the hose it will form threads and basically seal up. You just push it into the hose and not cut threads. Another option would be drill a hole in the tank for a short piece of tubing or a fuel line that has a grommet around it just cut off the hose on the inside of the tank about a half inch. then use the barbed fitting echo style vent goes on the end of a short piece of hose. I’ve used several of those and they work really well. tuck it up inside by the carburetor somewhere to get it out-of-the-way
     
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  16. backhoelover

    backhoelover Free service manuals and service tool info

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    drill a hole in take and use some fuel line and a echo tank vent
     
  17. backhoelover

    backhoelover Free service manuals and service tool info

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  18. Snap

    Snap ArboristSite Operative

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    Same here. Impossible to start after a layup without a prime in the cylinder.
     
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  19. Snap

    Snap ArboristSite Operative

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    Was a bit reluctant to drill the tank not knowing the wall thickness (vs grommet slot width) but I think it's coming to that. Thanks.
     
  20. Snap

    Snap ArboristSite Operative

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    The gas tank is the bottom of the oil/gas duo and they both face the chain so it's tough to find a spot to get a hose out and have a filter in a safe. clean location.
     

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