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I was running the trimmer I had just bought 2nd hand. I ran it great for about 10 minutes when it suddenly throttled high. I released the gas right away and it died and hasn't started again since despite much effort. Here's what I've done:

  • I verfied spark at the plug by pulling the plug while maintaining connection, holding the hex area to the cylinder wall, pulling the start and observing sparks at the business area of the plug
  • I verified gas getting to the cylinder by removing the spark plug and being able to sling liquid off it (I had just done multiple pulls with the throttle fully pulled)
  • I replaced the diaphram, metering valve, lever and spring (items 4,5,7,8,9,10,26, & 27 in breakdown below:enter image description here

Here is the troubleshooting chart for the trimmer:

enter image description here

I assume that the "high tension cord end" is the connector at the spark plug. I'm not exactly sure how to test that. I pulled the plug cap and held it close while pulling the start, but observed no spark. Can someone confirm how to perform that particular check, or confirm that it is unnecessary because I found spark at the plug electrode?

Also, can anyone give me anymore guidance? Of the 100's of pulls I've done since the original incident, I never one time got a single fire from the engine despite every possible choke configuration and lean or heavy throttling.

By the way, while changing the parts I listed above, I thoroughly cleaned the carb.

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I had a similar issue on an older unit - replaced ALL the fuel lines (along with what you did) and it works well now. I had fuel as you did, but it seemed to not flow correctly. –  Mark Schultheiss Jun 1 '11 at 15:23
    
This might get answers on Mechanics, or it might get closed there since it's not a "vehicle". In my opinion it would be a better fit on Mechanics, but I'm not sure how the community over there would feel about that. –  Tester101 Jun 17 '11 at 12:22
    
@Tester101: It would probably be off-topic on Mechanics. Relevant meta.mechanics post –  Vebjorn Ljosa Jun 23 '11 at 18:07
    
@Vebjorn Ljosa: weird... mechanics don't like small engines I guess. I would have thought a community of mechanics would know more about engine repair/maintenance, than a community of home improvement enthusiasts. –  Tester101 Jun 23 '11 at 18:36
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My problem with these things is I almost never mix the two cycle oil correctly with gas. If your trimmer takes two cycle oil mixed with the gasoline make sure you aren't overlooking that step. –  cfeduke Jun 26 '11 at 15:49
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The fact that it sped up right before shutting off tells me it ran lean. My first inclination would be to an air leak, most likely at the intake manifold or exhaust manifold. Check the gaskets and the bolts to make sure they are intact/tight. Also I'd also check the gap on the spark plug. Does the compression feel the same when starting as it did before it quit running?

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I plan to check compression as my next troubleshooting path. I assume you mean with a gage, which I haven't ever tested before. I did hold my thumb over the plug hole to kinda feel it, but not having tried prior to trouble, I can't be sure using that method. I'm out of town right now, but when I get back in a couple weeks I'll have to check. –  Flotsam N. Jetsam Sep 26 '11 at 23:24
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You should be able to get a decent feel just by how much effort it takes to pull start it. Is it the same as before it quit running? –  Cody C Sep 27 '11 at 13:08
    
Yes it is the same –  Flotsam N. Jetsam Sep 28 '11 at 1:31
    
Still, you should check the compresssion to make sure its not worn out. –  BrianK Oct 27 '11 at 18:44
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