Idles ok
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Needs a rebuild and new gas lines

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A clogged carburetor is most commonly caused by leaving fuel in the hedge 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 carburetor and cause the engine to stall or run roughly.
If the engine is running fast (revving high):

Make sure that the choke is disengaged and the throttle hold has been reset by pressing the trigger. You can check the throttle cable to make sure there are no kinks found in it – however this requires a mechanical proficiency to strip down the machine uncovering the cable.

The first thing to do is to ensure that the battery is fully charged. If after charging the battery you are still experiencing the problem, then it may indicate a fault with either the battery or charger. The defective item will need to be replaced.
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.
A worn, dirty, oily, or improperly gapped spark plug can cause a weakThe job of the spark plug is to ignite the air/fuel mixture. A worn, dirty, oily, or improperly gapped spark plug can cause a weak spark, which can misfire or detonate and cause a loss of power.
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.
over time the arrestor can become clogged with soot which may cause the trimmer engine to stall. you can try cleaning the arrestor with a wire brush. but you may need to replace it with a new.
Checking for debris or damaged blades: Visually inspect the blades and confirm there is no debris stopping the blades from moving. If there is debris ensure the machine is powered off when removing any blockages. Check the blades for any damage as a damaged cutting blade could cause the machine to stop working.
As such, we recommend sharpening after every 50 hours of use or so, to ensure consistent cutting performance and to enable you to enjoy your hedge trimmer for a long time to come. You can also find all the important information you need about sharpening your hedge trimmer in the operating instructions.
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.
While using your Hedge Trimmer, it`s common for debris and sap to become lodged in the cutting blades. This can cause the blades to bind, making trimming more difficult, and even cause the engine to overheat.
Fuel Vein Blockage

Eventually the blockage can cause a complete stoppage of fuel going into the engine, therefore causing it bog down and stop. If you suspect you have a blockage, the best cause of action is to strip down the carburettor and blow down the fuel veins with an air line or air blower.

The 503939601 Air Purge does just what the part name says. It purges the air out of the carburetor. Then it forces fuel from the fuel tank and fuel line in to the carburetor.
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.
This can be due to corrosion, scratches or general wear. As a result, the cutting edges of the cutter comb of your blades are no longer sharp, reducing their ability to cut. Sharpening the blade is required to reface the cutting surfaces restore these sharp edges.
If your hedge trimmer engine idles, but stops at full throttle, you will need to check the following parts: the fuel lines, gasket, carb kit, carburetor, and spark plug. This is a relatively common symptom and our repair guide can help you fix it.
It`s not necessary to lubricate the blades of a hedge trimmer to prevent rusting because they are pre-hardened rust resistant steel. However, you can use a lubricant to clean the blades, we recommend a light spray on lubricant such as WD-40 to give a thin coating.
For best operation and longer blade life, lubricate the hedge trimmer blade with a lightweight machine oil before and after each use.
What`s the problem with hedge trimmers? Many people don`t realize that hedge trimmers can cause extensive damage to plants by creating split, jagged ends on branches and by cutting leaves in half.
With a severed cord, your hedge trimmer is virtually worthless. With a small amount of money and a little ingenuity, however, you can repair the cord and have the trimmer running. If the cord left attached to the trimmer is long enough to be useable, then you simply can add a new plug to its end.
Why would the engine only run while the choke is on or with repeated manual priming? An engine that requires the choking (partial or full) after initial engine warm up is an indication that the engine fuel air mixture system is out of adjustment.
The carburetor gasket prevents excess air from entering the engine. If this gasket is damaged, it can result in an engine that only runs with the choke on.
The choke lever has two settings: a downward diagonal line (if the engine is cold and hasn`t yet been used that day) and a vertical line (if the engine is warm or if the engine has been running).
A clogged carburetor is most commonly caused by leaving fuel in the hedge 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 carburetor and cause the engine to stall or run roughly.

Discover Relevant Questions and Answers for Your Specific Issue

the most relevant questions and answers related to your specific issue

How to sharpen stihl gas power trimmer
ANSWER : Sharpen with a flat file. Its a long process as each tooth has 2 cutting edges. There are companies that will do this properly at cost.

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Stihl h5 556 starts up but stalls when trigger pushed
ANSWER : Probably “gum” and “varnish” build-up plugging the TINY passages [called “galleries”] INSIDE your carb!!!!!

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I have a stilh hl75 long reach hedge trimmer will not start plug is fine pull rope it will start sometimes but will not rev take choke off and it dies plug gets wet but still wont start seems to have a slite leak from the carb help please.
ANSWER : Sounds like a fuel problem, check the primer bulb, primer base and may possibly need a carb kit, gaskets and diaphragms can deteriate over time

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How to repair clutch HS45 Stihl – RTO Weed Eater Hedge Trimmer 20cc, Reconditioned
ANSWER : I’m not familiar with your machine, BUT… most of those centrifugal clutches ARE NOT repairable, and must be replaced when failed.

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Hedge trimmer put away for winter. will run but not stay running. put in new diaframs for carb . same results. i am questioning the gas cap now. is it possible that it can cause a problem with keeping this trimmer running Paul
ANSWER : YES, this system relys on pressure and the ionic nature of gasonline to pull the fuel through the system. If the gas cap is off or damaged where a seal is no longer possible, try taping it up with duct tape and see if that helps

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My trimmer slows down when applied to material to cut; on its own it runs fine. its electric & feels like its going to stall when you’re cutting. what gives?
ANSWER : Take it apart and clean the slip rings and brushes

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Trimmer starts and runs for 15 seconds and stops. won’t start for a few minutes and does the same ,
ANSWER : Check the air filter, replace the fuel if it is last year’s, clean the spark plug or replace. Also lube the blade. Good luck…Lee

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Hedge trimmer goes dead
ANSWER : Most likely a fueling issue but could be something else, more detail on the condition of the machine would be great.

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