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Thread: Two stroke carb - a question for the small plant mechanics

  1. #1

    Two stroke carb - a question for the small plant mechanics

    Hi, am looking for ideas what might be wrong with my older Echo Brushcutter with Walbro WA175 carb (no primer bulb).

    Last year it was very difficult to start on the cord, but it did eventually and ran "OK" if not a little flat at trying to pick up revs. Once it got going at full revs it went great. Spark is okay, new fuel filter last year, very little use since.

    This year - will not start at all on the pull cord without putting some fuel into the carb after taking off the air filter. Still has decent spark. It then runs, then dies. Starts again on the pull (set at full throttle) without adding any more fuel to the carb, but dies again. Adjusting the H/L screws has no effect.

    My thoughts were perhaps a split fuel pipe, but I have replaced this and it hasn't helped. The fuel pump on the bottom of the carb has fuel in it, but it doesn't seem to be getting through to the cylinder. I have blasted out the holes on the carb with air, and replaced the gaskets and diaphragms on the carb, checked the H/L pins etc.

    Could it be the gasket (paper type) on the rear of the carb that goes to the cylinder could be the problem as this is the only thing I haven't touched yet?? It looks a little ropey (possibly original), but seems a reasonably good seal, but to my untrained eye I cant see why this would affect it the way it does?

  2. #2
    will it run with the fuel cap off?

  3. #3
    Sounds like old fuel that's gummed up the jets. Use new fresh fuel without any oil and flush through the tank and carb. Turn it over without plug in engine several times and dissolve all that grunge away - full choke and full throttle - you need the fuel to clear out the jets. Then put in a fresh fuel mix and flush it through a bit more. Give the plug a good clean and check it is gapped correctly. Replace and fire her up.

  4. #4
    It sounds like the tiny hole in the slow running jet is still blocked despite you blowing it out - there may be hard deposits in there that need to be got out.
    Ultrasonic cleaning may loosen it - you could use a thin copper wire strand to rod it out. - Don't use a steel pin or needle as they are hard & can easily deform the hole making it bigger changing the mix.

    Ian

  5. #5
    Common problem in older bikes with today's 'petrol'
    i found using a lighter to briefly heat the jet before ultrasonic bath worked best
    say 3 times quicker than u/s alone
    obvious precautions about making sure you aren't dipped in petroleum vapour or you could go up like a Roman candle
    dont laugh...people regularly accidentally self immolate like this...seriously

  6. #6
    Fresh fuel and heat the sparkplug under the grille until red hot.... First pull!!

  7. #7
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    You need to send it in to a shop where they will do a crankcase pressure test.
    Two strokes work in a different way to other engines and if the crankcase is not sealed, i.e. leaking seals or head gasket, it will not run.
    A clue it is leaking will be found behind the flywheel or clutch assy.
    If it shows to be good on the pressure test then don't bugger about with the carb, phone Rowena Motors and give him the carb number. What he doesn't know about carbs isn't worth knowing.
    If you are going to Ultrasonic bath it then try with cellulose thinners.
    Just get a new carb
    “Man surprised me most about humanity. Because he sacrifices his health in order to make money.Then he sacrifices money to recuperate his health. And then he is so anxious about the future that he does not enjoy the present; the result being that he does not live in the present or the future; he lives as if he is never going to die, and then dies having never really lived.”........Dalai Lama

  8. #8
    Have worked on many of these, get a new carb is the answer, we used to rebuild the carbs but they never lasted.

  9. #9
    Quote Originally Posted by RED-DOT View Post
    Fresh fuel and heat the sparkplug under the grille until red hot.... First pull!!
    Have put fresh fuel in, problem is the fuel is not getting into the Cylinder. Took the plug out and it was dry, no smell of fuel. Spark is good as its a new plug.

  10. #10
    Quote Originally Posted by kimh View Post
    will it run with the fuel cap off?
    No, didn't take it off completely, just ran it loose after breaking air seal.

    Quote Originally Posted by Heym SR20 View Post
    Sounds like old fuel that's gummed up the jets. Use new fresh fuel without any oil and flush through the tank and carb. Turn it over without plug in engine several times and dissolve all that grunge away - full choke and full throttle - you need the fuel to clear out the jets. Then put in a fresh fuel mix and flush it through a bit more. Give the plug a good clean and check it is gapped correctly. Replace and fire her up.
    Put in new fuel, checked fuel filter wasn't gunked up, only put this filter on last year.

    Quote Originally Posted by Yorric View Post
    It sounds like the tiny hole in the slow running jet is still blocked despite you blowing it out - there may be hard deposits in there that need to be got out.
    Ultrasonic cleaning may loosen it - you could use a thin copper wire strand to rod it out. - Don't use a steel pin or needle as they are hard & can easily deform the hole making it bigger changing the mix.

    Ian
    I will try the copper wire. Failing that I might try the US cleaning, thanks

    Thanks also to Teyhan, I've emailed Rowena Motors just in case they have a solution!

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