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Air in fuel line; how is it happening?

Discussion in 'Chainsaw' started by epicklein22, Mar 12, 2008.

  1. epicklein22

    epicklein22 ArboristSite.com Sponsor

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    Ok I have a stihl 041 farm boss that I have been working on. It has a new fuel lines from the tank to carb and inside the tank. It also has a new impulse line. The fuel line is clear, so I can watch the gas being pumped. I can get it to run off of some gas in the carb and it starts to pump gas but when pumping gas, I noticed there is air in the fuel line. How is this possible after I just put new lines on it? Is the carb the problem? Should I try the carb from my 041av? I was not able to find an answer using the search button. Thanks for any help because currently I am stumped.
     
  2. volks-man

    volks-man Arboristsite.com Spooner

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    $.02

    i had some trouble picking up fuel after changing a line recently.
    maybe you just need to keep trying untill you draw enough fuel to purge the line.
    my saw would not pick up the fuel for anything untill i choked it -completely-with my finger and pulled a thousand times or so! now it will start and run on demand.
    maybe this will help but, i'm certainly no saw mechanic.

    paging mr. lakeside........................................:)
     
  3. Bob Wright

    Bob Wright Addicted to ArboristSite

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    Maybe your carb diaphram has a pin hole in it.
    Are we done shoveling snow in NEOhio yet?...Bob
     
  4. kevin j

    kevin j Addicted to ArboristSite

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    are you sure it is air bubbles, not fuel cavitating/vaporizing? If the inlet filter is plugged you can get vapor bubbles. Do they disappear after sitting a while? Vapor. If still there, air.

    Any joints, barbs, etc leakig, or filter hung up in the tank above the fuel level?

    k
     
  5. Joggerjack

    Joggerjack ArboristSite Lurker

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    You need to prime the line. Fill the line with fuel before you install it. Hold your finger on the end so the fuel doesn't leak out, install one side, then hold your finger on the other end and install the other side. The air in the line stays in the line, it's not a leak, it's the air already in there. Or maybe install one side and get a thin funnel, fill the line with fuel, and install the other side.
     
  6. Joggerjack

    Joggerjack ArboristSite Lurker

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    I do this trick when I change fuel filters on the dozer. Shop manual says install it dry and open the drain cock and wait 5 minutes for the filter to fill with fuel by gravity. Heck with that, I fill the filter with fuel before I install it and save 5 minutes.
     
  7. epicklein22

    epicklein22 ArboristSite.com Sponsor

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    I made sure everything looks good, filter on the bottom, no kinks. The air does not disappear. I think I will check the inlet screen next.

    I will also try priming the line.
     
  8. kevin j

    kevin j Addicted to ArboristSite

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    sorry, I assumed there were bubbles in the line but generally liquid filled. If all air, defintely prime it. Or blow in the fuel tank opening to push fuel up the line, then connect to carb when fuel is coming out.

    and 'don't inhale' ....


    k
     
  9. stihltech

    stihltech Addicted to ArboristSite

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    elbow

    The plastic elbow has a crack in it. Find a new or good used one.
     
  10. Lakeside53

    Lakeside53 Stihl Wrenching

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    and.. no need to prime the lines.. it will suck through very quickly.
    Fish the filter out of the tank, and pressure test the line from the filter connection to the carb.
     
  11. epicklein22

    epicklein22 ArboristSite.com Sponsor

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    Well, I just tore the carb down and everything looked good inside. I got it to run full open on full choke, but nothing else. With the saw pulling air, it makes sense that the saw will only run with full choke. I thought the plastic could be a problem, I will grab a replacement off of a 031 or 032.
     
  12. Kenskip1

    Kenskip1 Addicted to ArboristSite

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    On my 041 I also replaced the gas line and filter. The gas line is also clear. I have no troubles but I have had air in the line.What I suspect is that the gas line is slightly higher than the port the line goes into. Simply, the air will rise to the highest point.I have not had any issues with this.You could have an air leak like the past members suggested. Ken
     
  13. Lakeside53

    Lakeside53 Stihl Wrenching

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    Running only on choke is a symption of low or no impulse pressures....


    Pressure test the fuel lines and if they are o.k. the saw.
     
  14. czar800

    czar800 ArboristSite Operative

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    What he said, I just had a 024 doing the same thing and i found a bad impulse line.
     
  15. epicklein22

    epicklein22 ArboristSite.com Sponsor

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    The impulse line is new. I swapped out the plastic elbow and check the lines, everything is good. The elbow that came on the saw looked like it was fine though. I was finally able to get it to run half way decent w/o choke and now I think it just needs the carb fine tuned. It was pumping air in the begining and then the bubble slowly got smaller and disappeared, except I don't know what fixed it. I will report back if something else pops up.
     

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