4-cycle TroyBuilt trimmer won't run full throttle, ideas?


Old 05-07-08, 11:32 AM
Thread Starter
Join Date: Oct 2005
Location: Ohio
Posts: 52
4-cycle TroyBuilt trimmer won't run full throttle, ideas?

Last year I bought a new straight-stick type 4-cycle(no mix) TroyBuilt line trimmer. It worked great.

However now it's spring, I went and refilled it with oil, put in new gas, and it did in fact start in the choke, and it'll run like that only slightly puttering. But when I open the choke and squeeze the trigger to rev it up to a good cutting speed, it dies after about 5 seconds.

I've already checked the carb, and that was free of any crud, and the sparker is only slightly blackened.
I really just can't think of what else to check... it's not a overly complex machine so there's not many parts to go wrong, but it just won't run right.
Possibly getting too much air to fuel mix? visa-versa?
Idles fine... just won't rev up.
So anyone have any ideas?

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Old 05-07-08, 03:11 PM
Join Date: Jul 2005
Location: Texas
Posts: 205
I had the same trouble,found that the valve clearence was out of adjustment,the exhaust valve clearence was to close,adjusted the valves and it ran great.Check your owners manual for valve adjustment.Hope this helps.

Old 05-07-08, 11:45 PM
cheese's Avatar
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Join Date: Jul 2001
Location: USA
Posts: 16,821
I'd suspect the carb has a fuel restriction in it.
Old 05-08-08, 05:36 AM
Join Date: Feb 2008
Location: usa
Posts: 755
I suspect you have a carburetor problem due to old fuel. Fuel for 4 cycles need to have fuel stabilizer added to help prevent carburetor problems. Fuel actually goes bad rather quickly.

I am thinking your trimmer has a WY Series Walbro Barrel Valve Carburetor. Go to the Walbro link and download the Walbro Service Manual for Diaphagm Carburetors. Every detail you will need to know to repair your carburetor is in this manual.


Good luck to you
Old 05-08-08, 05:23 PM
Thread Starter
Join Date: Oct 2005
Location: Ohio
Posts: 52
Thank you all for the advice, I did in fact fix the machine and it runs great again.
The problem as it turns out was in fact the air-intake valve wasn't opening, so kudos to "jsouth" and secondly I got out a magnifying glass and inspected the carb after I took it apart and there were a few grain particles of... something green?... just inside where the screen meets the diaphragm. So big kudos to Airman for the great info and link!
So a little cleaner, a little shot of compressed air blow and a 1/4 turn on a rocker arm nut and the machine is as good as new.

Thanks! I really appreciate that this forum is here and that it has such knowledgeable people!

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