Shindaiwa T20 string trimmer runs better upside down?

jbclem(z9b Topanga, Ca)June 9, 2010

It's always difficult to get this T20 to run, but once warmed up it will run ok for a while. But after five minutes or so it will act like it's starved for fuel and shut off...unless I turn it upside down. If I do that just right, upside down for 30 seconds or so, then I can go back to right side up and it will work for a while until the same proceedure repeats itself. Sometimes it will run for many minutes, but always ends up starting to shut off which I can usually cure by turning it upside down. Sometimes when it shuts off, it won't start for a while, unless I use starting fluid (such as SureStart ether).

I've done the usual things, replaced/rebuilt the carb kit, cleaned out the muffler and made sure the exhaust outlet isn't plugged, adjusted it a million times. Replaced the fuel filter, run it without a fuel filter, run it directly from a hose to a tank of gas.

Since it seems to run ok when I connect a hose directly to a tank of gas, I suspect a problem with the fuel tank/breather system. But I don't exactly know how this works and what is most critical (ie, could a minute crack in the plastic tank affect the running, does the fuel cap gasket have anything to do with breathing...).

Could someone suggest how I would troubleshoot for this kind of problem, and especially what I need to check in the fuel tank system.


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jbclem(z9b Topanga, Ca)

Forgot to mention, I've also cleaned, replaced, and run it without the air filter...this hasn't affected this problem.

    Bookmark   June 9, 2010 at 9:16PM
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You should take the muffler off and clean the exhaust port and the muffler spark arrester screen to complete the maintenance.

It is common for the new trimmer to run better up side down. But yours is an old model and since you have adjust and clean the carb, running too lean might not be the problem.

If the gas cap have issue on the vacuum, when it start choking, loosen the gas cap to see it make the difference. If so, look into the gas cap.

Also jiggle the spark plug wire with a wooden stick ( not pencil as graphy conducts) and see whether you can change it.

If all else fail, open the carb and clean one more time, but this time, get a can of compressed air in computer store and blow dry all the little openings and parts before putting it all back together and see what happened.

    Bookmark   June 9, 2010 at 11:59PM
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jbclem(z9b Topanga, Ca)

After reading your reply I remembered that after many carb adjustments and cleanings, I replaced the carb with a new one. I've also removed the muffler, cleaned the port, the screen, and I've run the trimmer with a loose gas cap. None of these changed the problem. I've moved the spark plug wire hundreds of times, tapped on the electronic unit, checked all the wires...

Just used the trimmer would run for a while then start to loose power quickly. If I was fast, and turned it upside down, it would usually regain power upside down and then I could righten it and use it for a while longer(5 mins or so) before it would start to loose power again. Sometimes it would die before I could turn it over. It was always easy to start up again but sometimes I'd have to play with the hand control to keep it idling.

    Bookmark   June 12, 2010 at 3:50AM
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Wow, I think you run out of easy fix!!!

Did you check for cracks on the fuel lines? crack on the block that separate the carb from the hot cylinder?

Now you are getting into more difficult things like leaking vacuum seal around crankcase and bearing. Also seal between the cylinder and the crankcase. Setting up test for that is not as easy. Someone here might have an easy way that I cannot think of.

One thing you can try is removing the spark plug and turn the engine by hand. If you have a good vacuum seal, you should feel resistance on the down stroke, not as hard as the compression ( up ) stroke. Maybe with some soap solution around the seal and turn the engine to see any bubbles. Someone might have better ideas other than to hook a pump to the intake or exhaust port to pump.

If all else fail, maybe is time to think "new toy"!!!

    Bookmark   June 12, 2010 at 2:51PM
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Looking up your trimmer, the diagram shows that your T20 has the same carb as my old Stihl FS80 - a TK carb.
the fuel line connects to a round part held on with 3 screws.
This part is the fuel pump. It doesn't use crankcase pressure to pressurize the tank pushing fuel into the carb like today's trimmers. This diaphragm pulls fuel up to the carb.
Thats why turning it upside down solves your problem - gravity does the work instead.
Look up carb rebuild kit for TK carbs to replace the diaphragm.

    Bookmark   June 13, 2010 at 12:12AM
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But he changed to a new carb already.

    Bookmark   June 13, 2010 at 1:29AM
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Same exact problem with my Echo trimmer with PAS225 engine. Runs great upside down but sputters and won't accelerate when right-side up. I've checked everything. By the way, is there a high-speed adjustment on this thing? The manual does not mention one, nor can I find one. Idea?

    Bookmark   March 26, 2013 at 6:07PM
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I had the same problem with my fs80. i tried a carb rebuild kit with no luck. I replaced the carb with a used Walbro off a NEW fs80. just drill a new hole for the new second hose back to the tank and problem solved.
Same solution for my fs 65s which are gravity fed.

    Bookmark   April 1, 2013 at 9:52PM
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