Small Two-Stroke Weed Eater

Discussion in 'Off-Topic' started by tindel, Jun 22, 2015.

  1. tindel

    Thread Starter Active Member

    Sep 16, 2012
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    Someone here has to know something about small two stroke motors. I can get the thing to start and I can open the choke and it will idle at max power okay. If I literally just rotate the motor a bit it will stall out.

    I cleaned the carb last summer hoping it would help - it didn't. I used the dremel to put a notch in the port adjustments so I could play with them. On the one on the left of picture #1 If I adjust it a 1/16 turn CCW it helps it to start... if I adjust the second one ~1/2 to 3/4 turns CCW it helps the idle a better. Any other ideas?

    Don't really want to spend another couple hundred on a perfectly crappy weed eater.

    Frustrated and pissed off.

    [edit] and I can't seem to upload my pictures either... they are jpeg, but they don't display when I hit 'upload files'.
     
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    I'll bet it got put away with ethanol gas in it last season...
     
  3. debe

    Well-Known Member

    Sep 21, 2010
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    Ive found in most small 2 stroke carbys its beter to just replace the diaphrams & gaskets as a kit. They are cheap enough & generaly fix problems of adustments not working properly.
     
  4. Brownout

    Well-Known Member

    Jan 10, 2012
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    I tried unsuccessfully several times to clean the carb on my lawnmower, until finally I noticed the tiny emulsifier tube pressed into the body. I pried it out with a screwdriver (it was a press fit) and saw it was covered with a crystalline substance. Once I cleaned it and reassembled the carb, the mower ran fine. Moral: it's easy to miss small parts when you're cleaning your carburetor.
     
  5. tcmtech

    Well-Known Member

    Nov 4, 2013
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    Have you checked your fuel line and how it is positioned inside the fuel tank?

    I had a similar issue with one of my chainsaws a few years ago that would do a similar thing and I eventually tracked it down to the fuel line and internal weight/filter device in the fuel tank. The fuel line had somehow gotten pull out just far enough for the weight to not be able to move to the bottom the tank when held in a certain position causing to to run out of gas every time I tilted it.

    Option two is a pinhole in the fuel line inside the tank causing a similar problem when ever the fuel moves away when tilled.

    Option three is as other have said. carb diaphragm or plugged fuel/breather lines.

    Option four would be something is shorting out the magneto or the kill switch when the unit is tilted a certain way.

    That's my thoughts being if it can run at full power in one position then immediately shuts off if put in another.

    If tilting it causes an instant shut off then it's likely an ignition/magneto/electrical problem.
    If it stalls out a second or so after tilting its likely a fuel delivery problem.
     
    #12 likes this.
  6. Randy 7140

    Member

    Jun 17, 2015
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    A great trick I use every year on all of my gas powered machines........ Get some Carb/Choke cleaner from the auto parts store and spray some directly into the gas tank, prime it well and try again..... It will clean all of the lines and the carb from the inside without disassembly. I've had really good success using this on two/four stroke motors that will not start. That cleaner is a solvent and will burn clean with the gas. Good luck.
     
  7. #12

    Expert

    Nov 30, 2010
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    Spraying random solvents into a plastic fuel tank makes me worry about dissolving the fuel tank and moving the newly created sludge into the carb. Please be specific about which carb cleaners you know about and trust. Perhaps a test spray on the outside of the fuel tank is a smart precaution.
     
  8. Randy 7140

    Member

    Jun 17, 2015
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    Ive never had a problem with the solvent eating away at the plastic tanks and I've done this for years on the same machines. Certainly test it first on the outside if you'd like. And the sludge will have to work its way out one way or the other. The type I use is the "Gumout" brand.

    https://gumout.com/maintenance-aerosols/carburetor-choke-cleaner/

    It WILL however affect and dissolve rubber seals, so stay away from those. Good luck
     
  9. #12

    Expert

    Nov 30, 2010
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    This is where my head starts hurting. How do you know a carburetor doesn't have any rubber seals in it? Gasoline would eat them?
     
  10. alfacliff

    Well-Known Member

    Dec 13, 2013
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    a very commmon problem with those engines and chainsaw engines is worn crankshaft seals or bushings. air leaks casue the engine to lean out. theyy suck the fuel air mixture in to the crankcase when the piston goes up, and force it into the cylinder when the p;iston goes down. any leaks in the crankcase will cause the mixture to be way off. common symptom, runs with choke on, dies when choke turned off.
     
    #12 likes this.
  11. Randy 7140

    Member

    Jun 17, 2015
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    I've never saw a carb that had rubber seals. Mostly flat gaskets that are not made of rubber. The rubber seal on the gas tank cap is what I was referring to.
     
    #12 likes this.
  12. tcmtech

    Well-Known Member

    Nov 4, 2013
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    Very few modern diaphragm type carburetors are made that don't have neoprene rubber for their internal seals and diaphragms.
    Same with the plastic fuel tanks. Any decent brand unit is going to have a HDPE or other chemically resilient dense plastic for it's tank.

    The biggest chemical incompatibility issue is usually in the cheap vinyl or synthetic rubbers used for the fuel lines not being universally compatible with the fuels and cleaners they may get exposed to. They can dissolve into goo, dry out and become brittle and break, or swell up and leak or do one then the other.
     
    #12 likes this.
  13. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    One other thing that no one has mentioned is the air return line from carb to the tank. Or the rubber grommet it goes through. The return line is to pressurize the tank to force fuel to the carb. A leak will not allow it to pressurize and no gas gets to carb after the prime (bulb) runs out of fuel. My Ryobi mini tiller did this last year.
     
    #12 likes this.
  14. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    I have a two stroke blower that has a very similar problem. It will start and run until it warms up, but then will only continue running if I turn it upside down. It is a 32cc MTD engine that used to be widely used on Ryobi trimmers, etc. I really like these little engines, but I haven't had much luck rebuilding the carbs; parts are hard for me to get.
     
  15. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    I have visited the Mecca of 2-stroke engine manufacturing in Texarkana and the design engineers told me something that caused me to figuratively fall off my chair. Those consumer 2-strokes are designed to a 30-hour lifetime (at full throttle). Only the Stihl and Echo brands exceeded the "standard" at the time but they were not consumer grade at the time (7 years ago). It appears both companies have introduced models into the consumer market since then.

    Most people have 24 cutting weeks per year and use a tool like that for 10 minutes or less. Do your own math but 5 to 10 years and they are done. Less if you have a big yard or live somewhere with more cutting weeks per year.

    As for carb cleaners, ketones (acetone and methyl ethyl ketone (MEK) )seem to be in most and will cause damage to ABS and some nylon parts. Will usually leave polypropylene and polyethylene alone. The broad term Vinyl" is always suspect, as are some of the acetal ( POM) and less common fuel line polymers selected for cost, flexibility or abrasion issues.

    As for rubber, who knows? It is such a formulated mess that every application behaves differently. Viton is kind of indestructible and a good carb (mikuni) will have viton o-rings when needed.

    Cheers
     
  16. wayneh

    Expert

    Sep 9, 2010
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    I've wrestled with small 2-strokes for over 30 years and in my experience, the usual problem is failure of the small carburetor. A no-start can be the spark plug, but a "runs badly" is the carb. Pouring gas directly into the throttle will tell you the difference. If it starts but then dies, the electrical stuff is OK.

    The tiny carburetor ports are easily gummed up and the main diaphragm gets old. This reduces pumping action, and it may not operate the little valve that is actuated but the diaphragm. A gasket kit usually solves things.

    Modern engines have those blankety-blank adjustment needles that you can't move without a special tool. So stupid. Right now I have to run my weed whacker with the choke full on just so that it will run (poorly, at that). If I could back out my mixture screws, I'm sure it would run good as new again. And you can't do a thorough job on a carb rebuild without backing those needles out and cleaning out those holes.

    I've had fuel lines break or slip off, primer bulbs crack, and so on. But those are once-in-a-decade kinds of things. The carbs usually fail every 2 years or so.
     
    Last edited: Jun 23, 2015
  17. tindel

    Thread Starter Active Member

    Sep 16, 2012
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    This thing is brand spankin' new. I bought it about 3 years ago. and it never ran right last year. I made sure to get all of the gas out of it last year so I'm pretty sure the carb should be okay still after cleaning it last year. I mean it's running with the choke! Maybe I should tear it down again though and just give it a good spraying with carb cleaner again though. I have no problem replacing the gaskets (one is rubber, and another a dark mylar sort of thing), but Ryobi doesn't offer servicing parts and sourcing them from China will be 2-3 weeks.

    Also - I disconnected the fuel lines from the carb and blew threw both of them to make sure there was no gumming there. My fuel is last years fuel - so maybe it's started to gum up in the tank. Since I'm in CO, I only have to use this thing three times a year. Once after the rainy season, and twice through the summer months. So I don't use much of the gas from year to year.

    I'm starting to think that having 2 or 3 of these in the garage - and hoping one works at any given time of year is my best shot. I need to weed eat soon... and some time constraints are starting to pop up where it's more important to get it done than having the time to fix it.


    Still don't know why I can't upload my images.
     
    Last edited: Jun 25, 2015
  18. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    For the gas problem, they sell premixed gas in quart cans that would be perfect for you. Pretty sure it is nonleaded and no ethanol. https://www.google.com/search?q=premixed+2+cycle+gas&ie=utf-8&oe=utf-8 Some what expensive but if your only using a small amount of gas per year, it's cheaper then repairing a motor, from using old ethanol gas.

    For parts I use these guys to find the part numbers, they have the most and best parts schematics that I've found. For all brands a very good resource. http://www.ereplacementparts.com/ryobi-trimmer-parts-c-7931_15633.html
    But their prices are high, so after finding the numbers there I then Google them for the best prices. But some stuff they are the only ones stocking the part.
     
  19. wayneh

    Expert

    Sep 9, 2010
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    I had good luck ordering carb rebuild kits from here. Fast and cheap.
     
    shortbus likes this.
  20. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    Thanks for the link. I'll give them a try.
     
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