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Experienced gardeners share their insights in answering this question :
Bogging issues tend to be fuel related. Check the fuel system from the filter to the carb, check the carb isn’t blocked, check the exhaust is clear so that the gasses can escape.

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One reason why one of these trimmers may die at full throttle is that too much oil is in the gas, which causes poor combustion. Improper operation, including overuse of the choke, can also be responsible. Poor combustion produces carbon deposits that foul the spark plug and exhaust port, making the problem worse.
If your trimmer engine idles, but stalls on throttle, check the following parts: the gasket, primer bulb, fuel filter, air filter, fuel vent, fuel line, and carburetor. The repair and symptom guide will help you better identify the part needed to be replaced and how.
Just Like Spark plug fouling, too much oil in the gasoline, inferior oil, a dirty air filter and/or continued operation at less than full throttle will plug the screen with carbon deposits. This prevents exhaust gases from flowing out, which leads to power loss or not running at all.
A clogged fuel filter is most commonly caused by leaving fuel in the string trimmer for a long period of time. Over time, some of the ingredients in the fuel may evaporate, leaving behind a thicker, stickier substance. This sticky fuel can clog up the fuel filter and cause the engine to stall.
If the engine is not revving up and cuts out before you reach higher revs then you need to do the following checks: Fuel: Make sure it is fresh and correctly mixed (see `Starting Issues`). Air filter: Make sure it is clean and unclogged. Fuel cap: Make sure it`s hand-tight.
When your trimmer starts and runs on choke, it could be because the check valve in the gas cap is clogged. Start the trimmer and gently unscrew the gas cap halfway off. Turn the choke off and assess. If the engine is still running, that means the gas cap may be the culprit.
Sometimes the spark arrestor screen can become clogged up itself. Common symptoms include lack of power, especially under load; poor acceleration; engine won`t come up to full RPM; and higher than normal “spit back” through the carburetor.
Trimmers Stopped working

If your trimmer won`t turn on, especially if it has not been used recently, you may simply have a drained battery. Plug your trimmer into your charger and see if anything happens. Ideally your trimmer will recognize it has been connected to a power source and charge its battery.

The most likely culprit is a dirty or clogged air filter. Issues with your fuel pump or fuel filter can also cause your engine to idle then die with any throttle. If you have an older car, it could also be a bad carburetor.
If the engine is not revving up and cuts out before you reach higher revs then you need to do the following checks: Fuel: Make sure it is fresh and correctly mixed (see `Starting Issues`). Air filter: Make sure it is clean and unclogged. Fuel cap: Make sure it`s hand-tight.
If your saw idles fine, and then bogs down when pressing the throttle, then adjust your `H` screw by unscrewing. This will increase the amount of fuel to the carburetor under load. If your saw idles fine, then runs lumpy with a lot of smoke when pressing the throttle, then adjust your `H` screw by screwing in.
If the filter becomes clogged, not enough fuel will reach the engine for it to run properly. Because your chainsaw will idle, but dies when it is revved up to full power, it means that the filter is only partially clogged; it will allow enough fuel to the engine to run on idle, but not enough to sustain full throttle.
The reason for that may be you`re using the saw at altitude or the carburetor adjustment has simply slipped. The saw also won`t operate well at speed if the air filter or spark arrestor or carburetor are dirty.
The fuel line may be clogged from stale fuel deposits, more reasons to cause your chainsaw to cut out when applying throttle. If a fuel line is cracked, it will leak gasoline and draw air from outside into the fuel line. If the line is leaking fuel, it needs to be replaced.

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My sthil fs 80 has new carb and new rings. has spark but wont start
ANSWER : Is fuel getting into the cylinder.? Is the spark continuous, check gap between flywheel and ignition module. 0.25 filer guage.

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Starts ok and runs ok after I have pushed in the choke but cuts out as soon as I touch the throttle. Can you help?
ANSWER : Sounds like the ethanol gas messed up your carburetor. Gotta hate this gov’t mandate to use this hazardous fuel. 10% ethanol =10% gas mileage reduction.
Stihl wont warranty any of their products that use ethanol gas. They want you to buy this very expensive ‘REAL GAS’ about $7 a quart

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Ms170 stihl chainsaw wont start or if it does start it wont take the throttle
ANSWER : Try new gas, and adjust the carb.

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My stihl weed eater fs85 hard to start when hot
ANSWER : Try loosening the gas cap to relieve any pressure, then tightening it back up. Usually you will just need to barely unscrew it and then screw it back even before you pull the rope.

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Saw will start but dies when rev – Stihl 16" Chainsaw Bar Chain Saw 018 025 Ms 180 250
ANSWER : Check the pick up fuel line in the gas tank. If there is a fuel filter at the end of the line,remove and clean or replace. Use a small fexible wire to hook line and pull out thru gas tank opening.

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Sthil fs 85 trimmer runs only on starting fluid
ANSWER : Check for breaks in fuel line, check fuel filter.

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I have a stihl fs 85r,it starts and runs fine for a few mins. then quits.i lets it sit for a half hr or so then it starts right up but quits the same way again?
ANSWER : Possible vapour lock in the fuel tank. pop the fuel cap when it stalls, its probably under vaccum, check tank vent.

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Starts then dies stihl fs45/weedeater
ANSWER : I sounds like it sucked up some debris in the bottom of the fuel tank and obstructed fuel flow somewhere. Start by blowing out the in-tank fuel filter (You will have to fish it out with something), then load the line with carb cleaner (wear safety glasses) put fuel filter back in line and crank it a few times to pull the carb cleaner into the carb. This may dislodge the obstruction. If this doesn’t work, you will have to remove and cleant he carburator. Hope this helps.

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