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Can't get my gas trimmer running... what am I not thinking of?

Post in 'DIY and General non-hearth advice' started by Bret Chase, Jul 7, 2013.

  1. Bret Chase

    Bret Chase Minister of Fire

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    I've got an old (formerly trusty) Homelite ST155 (UT-20539) that I've had for ages that I cannot get to start this year...

    This is what I've done so far: Rebuilt the walbro WT carb with the full repair kit from NAPA, new primer bulb, new tygon fuel line, new fuel strainer, new DJ7Y plug.

    It has spark, it has compression... and now at least the primer bulb will pump fuel. I rebuilt the carb in accordance with the walbro manual... setting both high and low needles to 1 1/4 turns out.... best I can get it to do is "fart"

    what am I not thinking of? it is irking me...

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  2. Backwoods Savage

    Backwoods Savage Minister of Fire

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    Sometimes those things just like to be ornery. Have you tried some ether? Also, I'm not so sure on those needle settings. Might want to double check what they should be.
  3. Bret Chase

    Bret Chase Minister of Fire

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    the needle settings came from the walbro manual.... I cannot for the life of me find a manual for the trimmer online.... no, I've not tried ether... yet
  4. ScotO

    ScotO Guest

    make sure you have hot spark, too. You may also have fouled the plug. Take the spark plug out, pull the rope 20 or 30 times, put spark plug back and and try to start it again.....
  5. jharkin

    jharkin Minister of Fire

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    If it fires with a shot of starting fluid but not otherwise then you know its a fuel draw issue. Did you make sure to have everything spotlessly clean while rebuilding the carb? The tiniest spec of dirt in a jet could cause issues. Also double check you put all the gaskets and especially the pump diaphragm ( the one with two flappers) are in the right orientation. And check to make sure you didn't block the pulse port to the crankcase (unlikely unless you rotated the carb 180 somehow)

    All else fails open the needles some more, maybe to 1 1/2 or 1 5/8 and try again.
  6. Bret Chase

    Bret Chase Minister of Fire

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    I am quite versed in carb rebuilding... though I will admit it is my first trip inside a Walbro WT. they are far more complicated than the stone axe roundslides in my Skidoo.... and nearly as complicated as the 4 keihins in my bike.

    I will go through it again...

    I do not like being vexed by a damned weedwhacker...
  7. charly

    charly Guest

    If you put in a different needle and spring,, the pop off pressure could be too high to allow fuel in.. For what carbs cost, it's worth just getting a new carb at times...Run seafoam in your gas mix,, it will start year after year...They make a spray you can use to get it started as well... Try another plug as well..Could simply have a new bad plug...Then you'll really be searching for a problem ;) Gap the plug to specs?
  8. Bret Chase

    Bret Chase Minister of Fire

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    it's the same needle and spring... the new one in the kit was twice as long as the old one.... and the original one appeared to be in good shape.

    the old pump diaphragm was definitely junk.... before the rebuild... the primer bulb did nothing....

    a new carb for it is $63.....
  9. semipro

    semipro Minister of Fire

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    As former mechanic I've probably rebuilt thousands of carbs including very complex models that many mechanics would not tackle.
    I gave up on rebuilding Walbros and their ilk though and just replace them now. (though I hate the thought of letting the little bastards get the better of me!)

    You might want to check around on that price. That seems expensive for that carb.

    Some two-strokes used to have reed valves that allowed air to flow only one way through the intake. Maybe yours does and its not working?

    Clogged exhaust port?
    charly likes this.
  10. Bret Chase

    Bret Chase Minister of Fire

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    looking at the exploded diagram... it's a plain old piston controlled port engine... no reeds or rotary valve...

    Maybe I should just swap in the K&B model airplane engine I've got sitting in a box on a shelf..... lol
  11. Bret Chase

    Bret Chase Minister of Fire

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    I can do pretty much any 4 stroke carb blindfolded.... though those 4 Keihins..... that requires a 6' table covered in white paper to keep track of all the parts
    I completely concur!

    it seems VERY expensive to me.....
  12. save$

    save$ Minister of Fire

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    I admire wanting to fix it. I have one hanging on my garage wall. I should say I have three. They don't work and I don't know anyone who wants them. Every time I work on one, I just get frustrated. Went out two years ago and got another one from Sears. Starts every time. My only complaint is that they are too heavy for anymore than 15 min. I also picked up an electric one that takes the attachments. Electric one is not so heavy and works so long as I don't cut the cord off.
    I recently saw an add on tv for a battery powered one that has wheels. That should help with the weight issue.
  13. Bret Chase

    Bret Chase Minister of Fire

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    I've got the homelite... and a B&D 18V that I got for my wife.......

    If you find yourself oh about 60 miles south of Chelsea on the pike..... I'll take the 3 trimmers.... I like to tinker... I will not let the homelite win!
    semipro likes this.
  14. charly

    charly Guest

    Maybe try to start it while holding the throttle open?
  15. charly

    charly Guest

  16. Hogwildz

    Hogwildz Minister of Fire

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    I had a similar issue with a Ryobi weed wacker. I found a new carb on either Ebay or Amazon for $20.00. Was not worth the hassle to rebuild, took old carb off, put new carb on, done deal.
    Did you try a new spark plug?
  17. Bret Hart

    Bret Hart Member

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  18. Bret Chase

    Bret Chase Minister of Fire

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    I didn't think of the base gasket.... I had that trouble with an old 35HP Chrysler outboard long ago...... I should have thought of that....
  19. Bret Chase

    Bret Chase Minister of Fire

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    I generally don't use champion.... but it was the stock plug.... and it was at walmart during a grocery trip.. I use delco in my GM's.... NGK in everything else....

    though my small engines tend to have whatever they had in it when I acquired them....
  20. TMonter

    TMonter Minister of Fire

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    Second on the NGK plugs. They just seem to hold up better in general based on past experience. I've had more than a handful of Champion plugs go bad after a couple seasons on 2-stroke equipment.
  21. Bret Chase

    Bret Chase Minister of Fire

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    yes, new plug.. I will rtv the base gasket before I start looking towards ebaying a different carb....
  22. maple1

    maple1 Minister of Fire

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    Going through this right now with a Jonsered spacing saw (same as Husky 235). All the ingredients seem to be there but it won't run - all it does is give a little 'sput'. Have a coil on order, even though there is some spark at the plug. Frustrating...
  23. semipro

    semipro Minister of Fire

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    You might want to check your exhaust ports, mufflers, spark screens for clogging.
  24. NE WOOD BURNER

    NE WOOD BURNER Minister of Fire

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    Try checking your spark with an inline spark tester with plug installed.

    Many times the spark gets weak just from corrosion at the pick up(emery paper).
    Check ground @ coil
    Clean all wire connections with electroclean

    Just a thought.
  25. Bad Wolf

    Bad Wolf Minister of Fire

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    I have a similar issue. Sears 31 cc weed wacker, 2 years old. It will "pop" with the choke on, when you then move it position "2" it will catch, rev and die. If I leave it run on full choke it will chug and looks like its spitting fuel out of the carb (walbros) . I've taken the carb apart and blown out every passage and I still get the same thing. A new carb is $35 and I only paid $113 in the first place. I'd hate to pay $35 wait two weeks and have it still not work. I'm about to pitch it in the river!!!

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