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TroubleshootingString Trimmer Repair

Why won't my string trimmer start?

On a gas trimmer the usual causes are old or wrongly mixed fuel, a stop switch left off, an unprimed carburetor, a dirty air filter or a fouled spark plug. On a cordless trimmer, check the battery: seated and latched, charged, dry and within its temperature range. Work through these in order before paying a shop.

Free to ask. Local shops send quotes, and you pay only when you book one.

By Kasra Taheri, Founder, LoclisPublished

Researched and drafted with AI, then checked claim by claim against the sources listed below before it was published. Prices and rules change; the dates beside each source say when it was last checked.

Step by step

Read when to stop and call a pro, further down this page, before you start.

  1. Step 1: Make sure the stop switch is on

    Move the stop switch forward, away from the STOP position.[1]

  2. Step 2: Check the fuel

    Fuel older than 90 days, unmixed or improperly mixed fuel can cause hard starting.[1] Empty the tank into an approved container and refill with fresh, correctly mixed fuel.

  3. Step 3: Prime the carburetor

    Pump the purge bulb until fuel is visible and flows freely in the clear return line, then pump 4 or 5 more times.[1]

  4. Step 4: Use the choke for a cold start

    Set the choke to the cold start position and pull the starter rope up to 5 times until the engine fires, then move the choke to run.[1]

  5. Step 5: Look at the air filter

    Disconnect the spark plug boot, open the air filter cover and replace a filter that is soaked with fuel mix, holed or packed with dirt.[1]

  6. Step 6: Inspect the spark plug

    Remove the plug and check it for fouling or wear. Clean or replace it and set the gap to 0.6 to 0.7 mm (.024 to .028 in) on the ECHO model.[1]

  7. Step 7: Check a cordless trimmer's battery

    Remove and reinstall the battery so it is fully latched, charge it, and keep it dry and between 5 and 40 degrees C (41 and 104 degrees F).[2]

  8. Step 8: Stop and take it in

    If it still will not start, or fuel is leaking, have a small engine shop look at the carburetor and fuel lines.

Start with the cheap checks

A gas trimmer that will not start is usually short of one of three things: good fuel, air or spark. The fixes below run from the most common and cheapest to the least. A cordless trimmer is simpler, and its battery is almost always the cause.

A string trimmer head lying in grass with red cutting line extending from both sides
Photo: StrangeApparition2011, CC BY-SA 4.0, via Wikimedia Commons

Before you touch anything other than the stop switch, make the trimmer unable to start. Virginia Cooperative Extension's rule for mowers applies equally here: "Disconnect the spark or electric plug before troubleshooting or repairing the mower."[4] ECHO's manual says the same: "ALWAYS stop engine, disconnect spark plug, and make sure all moving parts have come to a complete stop".[1]

Stop switch and fuel

Many no-starts are a switch left in the off position. On the ECHO model the instruction is "Move stop switch (A) forward away from the STOP position."[1]

Next, the fuel. ECHO warns: "Use of unmixed, improperly mixed, or fuel older than 90 days, (stale fuel), may cause hard starting, poor performance, or severe engine damage and void the product warranty."[1] Penn State Extension notes that "Engines that are rarely or seasonally used, such as lawnmowers or chainsaws, are especially prone to difficulties".[3] A trimmer that sat since last summer is exactly that.

If the fuel is old, empty the tank into an approved container and refill with fresh, correctly mixed fuel. Use the oil and ratio your manual names. ECHO's manual says to "Use 89 Octane [R+M/2] (mid grade or higher) gasoline known to be good quality", and allows up to 10 percent ethanol, adding that "Gasoline containing methanol (wood alcohol) is NOT approved."[1] Ethanol blends carry less energy than straight gasoline, since "Ethanol contains about 30 percent less energy per unit volume than gasoline",[3] but a normal E10 blend is not usually the reason an engine will not run. "Fuel is VERY flammable."[1] Do all of this outdoors, away from sparks.

Prime and choke correctly

Most trimmers have a purge bulb. ECHO's cold-start routine is to "Pump purge bulb (C) until fuel is visible and flows freely in the clear fuel tank return line. Pump bulb an additional 4 or 5 times."[1] With the choke closed you then "rapidly pull recoil starter handle/rope (D) until engine fires (or maximum five [5] pulls)", move the choke to run, and pull again until it starts. The manual adds: "If engine does not start with choke in "Run" position after 5 pulls, repeat instructions 2 - 5."[1]

Pulling many more times on a closed choke usually floods the engine. If you smell raw fuel and the plug is wet, leave it for a few minutes and try again with the choke open.

Air filter and spark plug

With the plug lead disconnected, open the air filter cover. ECHO says to replace the filter if "Air filter element is soaked with fuel mix", has "Air filter element has holes or other damage", or is "Air filter element is saturated with dirt".[1]

Then the spark plug. ECHO's instruction is: "Remove spark plug and check for fouling, worn and rounded center electrode."[1] Clean it with a brush or replace it, and "DO NOT sand blast to clean. Remaining sand will damage engine."[1] The gap on that model is "0.6 - 0.7 mm (.024 - .028 in)",[1] and your own manual gives yours. A new plug is inexpensive, so replacing a dark, oily or worn one is usually the better choice.

Cordless trimmers

If it is battery powered, work through the causes in Toro's troubleshooting table: "The battery is not fully installed in the tool." "The battery pack is not charged." "The battery pack is over or under the appropriate temperature range." "There is moisture on the leads of the battery pack."[2] The stated range is "5°C (41°F) and 40°C (104°F)".[2] Toro also says: "Always remove the battery from the tool when troubleshooting, inspecting, maintaining, or cleaning the tool."[2]

Stop and call a pro if

  • The engine floods again and again on fresh fuel, or it starts only with the choke closed. The carburetor probably needs cleaning or rebuilding.
  • Fuel is leaking. ECHO says: "Check fuel system for leaks due to fuel tank damage, especially if the unit is dropped."[1]
  • There is no spark with a good plug, or the pull cord is hard to pull or jammed. Those are ignition or engine problems.
  • The battery and charger check out but a cordless trimmer still will not run. Toro sends this to an authorized service dealer.

Getting help in Virginia

Before you spend money, read how much string trimmer repair costs in Virginia. If the problem was just worn line, see how to restring a string trimmer. Browse more small engine repair answers or local small engine repair pros.

When you are ready, describe your trimmer and local small engine shops can quote it.

Common questions

Why does my trimmer start and then die?
Often the fuel or the air supply: stale or badly mixed fuel, a clogged fuel filter, or an air filter packed with dirt. ECHO's manual lists fuel older than 90 days and improperly mixed fuel as causes of hard starting and poor performance. Fresh fuel and a clean or new air filter are the cheapest things to try first.
How long can gas sit in a trimmer before it goes bad?
ECHO's manual treats fuel older than 90 days as stale, and says to mix no more than you expect to use in 30 days, or 90 days with a stabilizer. Penn State Extension adds that seasonally used engines are especially prone to fuel trouble.
Can I use ethanol gasoline in my trimmer?
Check your manual. ECHO's allows gasoline with up to 10 percent ethanol, and does not approve E-15, E-85 or fuel containing methanol. Other makers set their own limits.
My cordless trimmer is dead even with a charged battery. What now?
Take the battery out and put it back in until it latches fully, wipe any moisture from the battery contacts, and let a very cold or hot battery return to a normal temperature. Toro's manual lists these causes and sends everything else to an authorized service dealer.
Is it safe to work on the spark plug myself?
Yes, with the trimmer off and the plug lead pulled first, as the manufacturer's manual says. Do not clean a plug by sand blasting. If you cannot get the plug out or the threads look damaged, a shop can do it quickly.

Sources

  1. [1] Grass Trimmer/Brush Cutter Operator's Manual, model SRM-410U, ECHO Incorporated. Checked October 28, 2026.
  2. [2] Flex-Force Power System 60V MAX String Trimmer, Operator's Manual (Form No. 3469-654), The Toro Company. Checked October 28, 2026.
  3. [3] Fuel Ethanol: Hero or Villain?, Penn State Extension. Checked October 28, 2026.
  4. [4] Lawn Care: Rotary Mower Safety (BSE-42P), Virginia Cooperative Extension, Virginia Tech. Checked October 28, 2026.

Want a pro to handle it?

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