Engine problem with TroyBilt string trimmer

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  #1  
Old 07-29-08, 01:09 PM
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Engine problem with TroyBilt string trimmer

I have the TroyBilt 2-cycle gas string trimmer (TB75SS) and recently I noticed that it was tending to not follow the throttle trigger as well as it should. Sometimes pulling the throttle trigger would not increase the speed right away or the RPMs would increase even when I did not pull the throttle trigger (the engine would start racing at full throttle). Then the trimmer stopped responding to the on/off switch. To turn it off, I had to unplug the wire connecting the spark plug to the engine.

Thinking it was something in the on/off switch and/or throttle trigger, I ordered new parts for handle assembly that included a new throttle trigger and on/off switch directly from ToryBilt (MTD). I replaced the old parts with these new parts, but the behavior is the same. This makes me think it is something actually with the throttle on the engine and/or the electrical connection of the on/off switch.

Any suggestions of what else I can check or try replacing part-wise?
 
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Old 07-29-08, 01:16 PM
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You should test the kill switch with a continuity tester to see if the switch is working. Unplugging the spark plug when the engine is running can cause the module to fail.

Check the throttle cable where it hooks to the carburetor throttle linkage and make sure it's operating the throttle on the carb. Check the carburetor and all the mounting hardware to see if everything is good and tight. An air leak around the carburetor or the base that it mounts to can cause erratic operation.
 
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Old 07-30-08, 10:30 AM
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Originally Posted by 30yearTech View Post
You should test the kill switch with a continuity tester to see if the switch is working. Unplugging the spark plug when the engine is running can cause the module to fail.
That's good to know and I will test the new switch. I only went to that measure of unplugging the spark plug when I had no other way to stop the engine. After replacing the original handle assembly with the new kill switch and throttle trigger, the kill switch did not stop the engine once it started again.

Originally Posted by 30yearTech View Post
Check the throttle cable where it hooks to the carburetor throttle linkage and make sure it's operating the throttle on the carb. Check the carburetor and all the mounting hardware to see if everything is good and tight. An air leak around the carburetor or the base that it mounts to can cause erratic operation.
Thanks! I'll check those items. I'm hoping this is something that can be repaired at less than the cost of replacing the trimmer. But first...have to accurately diagnose the cause.
 
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