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Hello,
Need help on Stihl fs 45 String Trimmer.
When I pull Trigger motor speeds up then decreases.
I changed Fuel Filter, Fuel, Sparkplug, Tried Adjusting Carburetor.
Would appreciate any help on this.

Sounds like the carburetor needs to be replaced. Carbs are cheap enough that it cost too much to attempt a rebuild these days.

Also be sure the fuel lines are all good and the primer bulb is not cracked.

Oh! One important thing that I forgot is to pull the muffler off and cook it with a propane torch to remove carbon deposits. I have saved quite a few just by getting the carbon out of the muffler.

If exhaust cannot get out, fresh air cannot get in to run the engine.

This problem happens when people don't mix their fuel properly.

Thanks, problem solved with replacing Carb.

volt said:

Hello,
Need help on Stihl fs 45 String Trimmer.
When I pull Trigger motor speeds up then decreases.
I changed Fuel Filter, Fuel, Sparkplug, Tried Adjusting Carburetor.
Would appreciate any help on this.

Click to expand...

Always try to keep OEM carburetor if possible, in this case a Zama. The muffler is not usually what clogs, it is the spark arrestor on the muffler.