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OT: Small 4 stroke carb repair

Discussion in 'Off Topic Threads' started by wireguy, Mar 23, 2009.

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  1. wireguy

    wireguy TS Member

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    I have a Troy-Built string trimmer. Today it suddenly wouldn't run in it's normal operating position (upright). If I kept it turned over so gravity would feed fuel through the fuel line it ran fine, and would for short occassional periods in the upright position but would always run out of gas at some point. I notice that concurrently the primer bulb won't suck fuel or fill, so a leak in the fuel delivery system that is keeping vacuume from pulling fuel from the tank seems the likely culprit. I pulled the primer bulb off and checked everything under it but can find no obvious air leak. Does anyone know what the engine uses to suck fuel into the system on this tiny 4-stroke engine and where the likely source of this air leak into the fuel system might be?
     
  2. sharhope

    sharhope Member

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    I have never worked on a troy built trimmer but I would check the carb diaphragm.
     
  3. birdtracker

    birdtracker Active Member

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    wireguy: I sent you a P.M on this subject. Make sure where the carb bolts to the engine isn't loose or gasket isn't cracked. The engines running is what draws the fuel thru it. Primer bulb should stay full. Birdtracker
     
  4. foghorn220

    foghorn220 Active Member

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    I have a Sthil but it is 2 cycle and it has to be run half choked most of the time to keep it running I put a new primer bulb and check for leaks but im sure it still has one somewhere.

    I guess with running it half choked makes it suck better.

    Might try that to see if it will run the whole time in the up right position.

    Guess going to have to re look at mine also.

    Wire Guy does your's have electric start on it I didn't know they made such a thing in a trimmer until I read about it.


    Foghorn
     
  5. ricks1

    ricks1 TS Member

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    Would guess you have a stopped up fuel filter or the fuel line is bad. They suck gas by the air flow when moter is running . Same as a gravity feed lawn mower. If it will run upside down check and see if fuel filter is still on the line If it is a gas / oil mix its a 2 stroke.
     
  6. wireguy

    wireguy TS Member

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    Thanks everyone. It is a 4 stroke. You gave me some ideas.
     
  7. wireguy

    wireguy TS Member

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    I finally re-positioned the gas tank so that it gravity feeds. Cut weeds about 40 minutes tonight and it ran fine that way. To make this work I flipped the cutting head and handle 180 degrees from their original positions on the shaft. Now the trigger control is on top and I operate it with my thumb. It works fine this way. Don't buy anything Try Bilt. The name was bought out and the stuff is now considered junk.
     
  8. ricks1

    ricks1 TS Member

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    If you want a Top of the line and have the money to spend Look at the Stil 130. I bought one last year. It is a ONE pass cutter. It dont matter what you want to cut . ONE pass and its gone. Its pricey' $500 but is truely a ONE pass cutter. I cut my trimming time in half or more. It is a one pull start and will cut on idle speed as good as most will at full speed.
    If its running upside down then it is the fuel line, most likly not tight on the filter or filter has come off and letting line "float" in tank
     
  9. stokinpls

    stokinpls Well-Known Member

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    That's what happened to my chainsaw. It would run fine with the tank full, but was starving for gas shortly afterward. Took the gas cap off and the end of the line to the starting bulb was way up near the top of the tank. Lengthened it with a piece of brass pipe and it never missed a beat the rest of the job.
     
  10. HSLDS

    HSLDS Well-Known Member

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    Stokinpls,

    Typically there is a small filter on the end of the fuel line in chainsaws. It is weighted so it falls to the bottom of the tank regardless of position (it resembles airiators for fish tanks).

    Sounds like yours fell off...

    If you shake the saw do you hear a noise (other than the brass tube) in the tank??

    Wireguy,

    You may have the same problem - OR - these engines typically use a diaphragm driven fuel pump (they bleed some pressure from the crankcase to drive fuel from the tank into the carb). The pressure of the crankcase rises and falls with each 'stroke' and hence makes a perfect power source for a fuel pump. This can be a diaphragm alone, or a spring loaded diaphragm - it will be held in place between the carb and the crankcase, or under a cover on the outside of the carb (a small gallery caries the pressure up from the crankcase). A small tear in this will render the pump useless. Sitting 'dry' for a long period tends to let these dry out and fail.

    Carb kits are usually under 5 dollars and should contain this fuel pump diaphragm (only replace the parts you NEED to replace). See if you can find the CARB on line (diagram) to see how it assembles/works.

    Sounds like Foghorn has one with a failing fuel pump - choke at 1/2 lets the carb help suck fuel as part of the air flow.

    Good luck all.

    David D
     
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