Fix Hard-Starting Two-Stroke Engines

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AMSOIL SABER® Professional Synthetic 2-Stroke OilAMSOIL Gasoline StabilizerAMSOIL Power Foam®
David Hilgendorf
by David Hilgendorf
May 24, 2024

Few things are more annoying than trying to start a gas-powered two-stroke engine when there’s work to do. Fortunately, two-stroke engines are pretty simple, so most DIYers with a few tools and some basic knowledge can perform the necessary troubleshooting to get their tools and equipment running again.

Top 10 Two-Stroke Applications

  1. Chainsaws: Tree felling, forestry and arboreal work.
  2. Pole Saws: Tree limb trimmer.
  3. Leaf Blowers: Clearing leaves and debris.
  4. String Trimmers: Grass and small plant landscaping.
  5. Hedge Trimmers: Hedge and shrub shaping and maintenance.
  6. Brush Cutters: Manage dense vegetation.
  7. Garden Tiller or Cultivator: Soil preparation.
  8. Water Transfer Pump: Irrigation and drainage.
  9. Outboard Motors: Small boat and watercraft propulsion.
  10. Dirt Bikes: Lightweight off-road motorcycles.

Internal-combustion engines require a steady supply of air and fuel to run properly and produce maximum power. Two-stroke oils with poor detergency properties can allow varnish and carbon deposits to build up in various places, which chokes off air and fuel delivery, causing the engine to lose power, run poorly, start hard and eventually fail to start at all.


1) Bad Gasoline

Gasoline can break down in as little as 30 days, especially if it contains ethanol. Storing your equipment in the garage over the winter without stabilizing the gas is a recipe for equipment that won’t start in the spring. Varnish and gum created by bad gas in the tank can also plug the fuel filter and restrict flow.

Solution: Clean or replace the fuel filter, drain the tank and refill with fresh fuel.

2) Dirty Carburetor

Once gas breaks down, varnish, gums and other debris can form inside the carburetor and clog the tiny fuel passages preventing fuel from reaching the combustion chamber.

Solution: Clean the carburetor by spraying AMSOIL Power Foam into the intake and letting it sit for several minutes to help dissolve the varnish. If it still won’t start, remove the carburetor and spray AMSOIL Power Foam directly into all openings, then reassemble.

3) No Spark

Oil and carbon deposits can foul the spark plug preventing it from firing.

Solution: Clean the deposits from the electrode with a wire brush or light-duty sandpaper or replace the spark plug.

4) Dirty Air Filter

A clogged air filter prevents the engine from receiving the oxygen needed for combustion. Tap rigid filters on a hard surface or blow compressed air from inside out to dislodge any dirt or debris.

Solution: Wash foam filters with mild detergent and replace paper filters.

5) Clogged Spark Arrestor

A small screen may cover the exhaust outlet to prevent sparks from exiting. This screen can become plugged with carbon deposits when using low-quality two-stroke oil, which leads to power loss.

Solution: Remove the spark-arrestor screen and spray it with AMSOIL Power Foam to soften the deposits before cleaning. Replace the screen if it’s clogged after cleaning.

Prevention: Superior Two-Stroke Oil

Low-quality two-stroke oil creates heavy carbon deposits and is the cause of many problems with two-stroke equipment not starting. Using a high-quality two-stroke oil that burns cleanly and helps prevent carbon deposits is one of the easiest maintenance practices to ensure your two-stroke engines start easily, run efficiently and last for many years.

AMSOIL SABER® Professional 100% Synthetic 2-Stroke Oil withstands high-temperature operation to fight carbon buildup in gas-powered two-stroke engines. Its excellent detergency properties fight power-robbing deposits to keep exhaust ports and spark arrestor screens clean for easy starting and maximum power.

In independent testing, AMSOIL SABER Professional mixed at 100:1 provided better performance and fewer carbon deposits than a leading competitor’s two-stroke oil mixed at 50:1, offering the convenience of one mix ratio for all your two-stroke equipment. Plus, it’s formulated with gasoline stabilizer to help keep fuel fresh during short-term storage.

You can save time and money and gain the peace of mind that your two-stroke equipment will start and run optimally all year long simply by switching to AMSOIL SABER Professional.

by David Hilgendorf

AMSOIL Technical Writer and 20-year veteran of the motorcycle industry. Enjoys tearing things apart to figure out how they work. If it can’t be repaired, it’s not worth owning.

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AMSOIL SABER® Professional Synthetic 2-Stroke OilAMSOIL Gasoline StabilizerAMSOIL Power Foam®