what fuel is best for a small engine?

Whether you have a leaf blower, lawn mower, chainsaw, snow blower, or generator, these products have one thing in common—they all use a small engine.

Using the right fuel for your small engine is critical to its performance and lifespan. The wrong fuel can lead to starting problems, loss of power, engine damage, and costly repairs. It can even shorten the overall life of your equipment. Just like you wouldn't use diesel in a gasoline car, small engines require specific types of fuel to run properly.

Wondering which fuel is best for a small engine? In this article, BISON explores the main fuel options for small engines, including regular gasoline, premium gasoline, premixes. We'll help you understand which fuel is best for different types of equipment and how to choose the right fuel.

What is an octane rating?

You must understand how an engine works to understand octane or anti-knock ratings.

4-stroke engine operation

1. The intake stage (the piston moves down) draws air and fuel into the engine cylinder.

2. In the compression phase (the piston moves upward), the engine piston compresses the air/fuel mixture.

3. In the power stage, the spark plug ignites the air/fuel mixture, causing an explosion that forces the piston downward (which drives the engine to work).

4. The piston moves back up in the exhaust stage to force the exhaust gases out.

In a 2-stroke engine, these stages still occur but are completed over two strokes (the piston moves up once and down once).

Manufacturers are increasingly building engines with higher compression ratios, which means the air/fuel mixture is more pressurized and explosive.

Higher compression leads to more efficient use of air and fuel, making the mixture hotter. This can cause the fuel/air mixture to burn spontaneously (without a spark) in a phenomenon known as knock or pre-detonation.

Knock can occur before the piston reaches the top of the cylinder, driving it down prematurely and causing poor engine timing and severe damage.

High-octane gasoline is specially optimized for high-compression engines to prevent knocking. The air/fuel mixture can withstand higher compression without igniting prematurely. Thus, octane measures a fuel's resistance to knocking on a scale of 1-100.

Choosing the right fuel for small engines

Small engines, like those in generators, chainsaws, and brush cutters, rely on different types of fuel to run properly.

Fuel for your outdoor power equipment must meet these requirements:

• Clean, fresh, unleaded

• Minimum 87 octane/87 AKI (91 RON)

• Gasoline containing up to 10% ethanol (E10) is acceptable. Ethanol-free gasoline is also fine and is the best choice for long-term storage.

Selecting the right fuel helps your engine last longer and perform better. Do not use unapproved fuel types or modify your BISON engine to run on alternative fuels. These actions can damage small engines and will void your BISON warranty. Different fuel types offer various benefits and drawbacks, so it's important to choose wisely. 

Regular unleaded gasoline

Using gasoline containing ethanol in outdoor power equipment, such as lawn mowers, chain saws, trimmers, and leaf blowers, can damage the engine and lead to costly repairs. Small engine equipment is best served by using ethanol-free gasoline whenever possible.

Today's gasoline often contains ethanol, a type of alcohol made from corn or other plants. Ethanol helps reduce emissions but can cause problems in small engines. Most gasoline sold today contains up to 10% ethanol (E10), but higher blends like E15, E30, E50, and E85 are increasingly available. Common types of ethanol fuel include:

• E10 (10% ethanol, 90% gasoline): The most common type of fuel, generally safe for small engines, but can absorb water and cause fuel system problems over time. Most motor gasoline is E10, and this is approved for small engines.

• E15 (15% ethanol, 85% gasoline): Not recommended for most small engines because it can damage fuel lines, carburetors, and seals. Ethanol content of 15% or higher can burn hotter and damage small engine components.

• E85 (85% ethanol, 15% gasoline): For use in flex-fuel vehicles only; using this fuel in a small engine can cause severe damage.

If using ethanol fuel, never exceed 10% ethanol (E10) and add a fuel treatment to prevent fuel separation. Using fuel with more than 10% ethanol is illegal in outdoor power equipment and can void the manufacturer's warranty.

Pros:

• A wide range of fuels at affordable prices

• Suitable for most small engines

• No special handling required

Cons:

• Ethanol can cause fuel system problems. It absorbs moisture from the air, which over time leads to phase separation (water settling at the bottom of the tank), carburetor plugging, fuel system corrosion, and damage to rubber and plastic parts.

• It degrades during long storage — separated ethanol can cause ignition problems and overheating, ultimately leading to irreversible engine damage.

To reduce these risks: Use fresh fuel, avoid long-term storage, and if storing for more than a month, consider using a fuel stabilizer or running the engine dry before storage to prevent the buildup of stale fuel. You can also use ethanol-free fuel whenever possible, especially in seasonal equipment.

Premium unleaded gasoline

Some high-performance small engines may require premium gasoline. Premium unleaded gasoline, which typically has an octane rating of 91-93, can reduce knock in high-performance engines. Octane measures a fuel's resistance to knock, not power or cleanliness, so premium fuel provides no benefit unless the manual specifies it.

However, most standard small engines have a lower compression ratio, which means they may not benefit from a higher-octane rating.

Most manufacturers recommend premium gasoline only if the engine is designed to run on premium gasoline. If your owner's manual recommends regular gasoline, upgrading to premium provides no measurable benefit and is simply a waste of money. Stick with the octane rating your manual specifies.

Regular octane gasoline also works well if you maintain your equipment regularly, keep the fuel fresh, and clean the carburetor.

Pros:

• May improve performance in some small engines

• Helps prevent knocking

Cons:

• More expensive than regular gasoline

• No real benefit if the engine does not require premium gasoline

Pre-mixed fuel blends

Pre-mixed fuel is a ready-to-use blend of gasoline and oil, designed specifically for 2-stroke engines, such as those in chainsaws and brush cutters. These fuels come in the correct fuel-to-oil ratio, eliminating the need for manual mixing.

Oil and fuel mixing for small engines

• 4-stroke cycle spark ignited engines: Do not mix gasoline with oil or modify the engine to use alternative fuels. This can damage engine components and void the warranty.

• 2-stroke cycle spark-ignited engines: mix a high-quality 2-cycle oil with gasoline at the ratio specified in your engine's manual. BISON 2-stroke engines use a 50:1 gas-to-oil ratio; if you are servicing another brand, check its manual — 40:1 and 32:1 are common on older equipment, and using the wrong ratio can cause engine seizure or plug fouling.

Pros:

• No need to mix fuel and oil manually

• Longer shelf life than regular gas

• Cleaner burning for better engine performance

Cons:

• More expensive than mixing your own fuel

• May not be as widely available as standard gasoline

Fuel quick reference decision table

Choosing the right fuel for your small engine depends on its design and usage. Always check the manufacturer’s recommendations to avoid engine damage and keep your equipment running smoothly.

Fuel storage tips

It may surprise you, but gasoline is only suitable for about 30 days. After that, volatile compounds in the fuel begin to evaporate, whether the gas is in the mower or the gas can. This process is driven by oxidation, which causes the lighter fuel components to evaporate first.

As the fuel evaporates, it forms a brown sticky deposit that eventually hardens into varnish, which can plug fuel lines and carburetors. Once your fuel system is compromised, you may notice signs of poor engine performance:

• Lack of power

• Difficulty starting

• The engine running poorly

To keep fuel fresh and prevent engine issues, store it properly. Treating fuel before storage helps reduce oxidation, minimize deposit formation, and manage moisture problems caused by ethanol blends. Stabilizing additives prevent ethanol from separating out of gasoline and attracting moisture that leads to corrosion. Just follow these steps for proper storage:

• Add fuel treatment according to instructions.

• Run the engine for two minutes to circulate the stabilizer through the fuel system. If stabilizer is added directly to a motor's tank, the engine should run for at least 3 minutes to circulate it.

• Store the lawn mower or equipment in a dry, clean place for up to 24 months.

• If you prefer not to use a stabilizer, drain the fuel into an approved container and run the engine until it stops from lack of fuel. Whichever method you choose, store fuel in a cool, dry place away from direct sunlight and extreme temperatures.

Conclusion

Choosing the right fuel is essential for keeping small engines running smoothly, extending their lifespan, and preventing costly damage.

As a professional small engines manufacturer in China, we understand the importance of proper fuel selection. Following the manufacturer’s recommendations ensures the best results while reducing environmental impact. Storing fuel correctly and using stabilizers when needed further protects your engine and prevents unnecessary repairs.

Take a moment to check your engine’s fuel requirements today. All BISON small engines are designed to run on fresh, regular unleaded gasoline with a minimum octane of 87 AKI and no more than 10% ethanol (E10).