By Graham FisherUpdated November 2026
A lawn mower that got rained on won’t start for a few predictable reasons: water in the carburetor bowl, moisture on the spark plug and ignition wires, a soaked air filter, or fuel that has been diluted. Most of these problems clear up with drying, a fresh spark plug and a little patience, but a quick-start product can help when the engine is cold, damp and reluctant to fire. The five products below were selected by checking manufacturer specifications, brand reputation and the kinds of owner feedback that come up repeatedly for each item. They are aids for getting a damp engine running, not replacements for finding the actual cause.
Our top picks at a glance
- 1
TOP CHOICEBest overallValvoline Starting Fluid, 11 ozView on Amazon - 2
TOP CHOICEBest for small engines on a budgetSTA-BIL Start Your Engines! Fixes Non-Running Engines, 2 fl. oz.View on Amazon - 3
TOP CHOICEBest for cold, damp morningsStens 752-942 Starting Fluid, 11 ozView on Amazon - 4
Best for larger mowers and outdoor power equipmentBlaster Chemical Lawn Mower Starter, 16 oz, Pack of 2View on Amazon - 5
Best for Lawn Boy ownersLawn Boy TRU-Start 20-inch Lawn Mower with Briggs & Stratton 140cc EngineView on Amazon
Our Top Picks
| Product | Best for | Key feature |
|---|---|---|
| Valvoline Starting Fluid, 11 oz | Cold-start and damp-engine situations | Aids quick starts in cold weather while lubricating upper cylinders |
| STA-BIL Start Your Engines! | Small engines and occasional use | Small, low-cost can that also works as a fuel system revitalizer |
| Stens 752-942 Starting Fluid | Outdoor power equipment in cold temperatures | OEM-style replacement rated to -65°F |
| Blaster Chemical Lawn Mower Starter | Frequent use and larger mowers | 16 oz size in a two-pack for repeated starts |
| Lawn Boy TRU-Start 20-inch replacement | Lawn Boy mowers with Briggs & Stratton 140cc engines | Model-specific fit for a single engine family |
Valvoline Starting Fluid, 11 oz
Helps engines start quickly in cold weather while lubricating upper cylinders. Valvoline Starting Fluid, 11 oz
Best for: Cold-start and damp-engine situations
This is a general-purpose starting fluid for people who want a well-known name for an engine that is slow to catch after sitting in wet conditions. It suits homeowners with push or self-propelled mowers who have already dried the spark plug and want a reliable aid for the final start.
Key specs
- Size: 11 oz aerosol can
- Purpose: Starting aid for gasoline engines
- Formulated to help engines start quickly in cold weather
Pros
- Recognized brand name in automotive and small-engine aisles
- Helps the engine fire when fuel delivery is marginal
- Large can lasts through a full season of occasional use
Cons
- Aerosol use calls for caution around hot surfaces and open flame
- Not a fix for water in the fuel; the fuel still needs to be drained
Bottom line: A solid default for most owners whose mower simply needs a boost after getting soaked.
STA-BIL Start Your Engines! Fixes Non-Running Engines, 2 fl. oz.
STA-BIL Start Your Engines! – Fixes Non-Running Engines – A Jump Start in A Can – Revitalizes Fuel System – Safe for 2 and 4-Cycle Engines – Ensures Quick, Easy Starts, 2 fl. oz. (21214)
Best for: Small engines on a budget
Owners who want a small, inexpensive can for occasional use will find this a practical choice. It also suits people who want a product that doubles as a fuel system treatment for engines that have been sitting.
Key specs
- Size: 2 fl. oz. can
- Labeled for 2-cycle and 4-cycle engines
- Marketed as a jump start and fuel system revitalizer
Pros
- Compact size fits easily in a tool drawer
- Usable on both 2-cycle and 4-cycle engines
- Brand known for fuel stabilizers used in storage
Cons
- Small volume runs out quickly if the engine needs repeated attempts
- Works best alongside drying and spark plug service, not as a stand-alone fix
Bottom line: A good pick for light use and for keeping a spare can on the shelf.
Stens 752-942 Starting Fluid, 11 oz
OEM replacement, replaces Gunk M3815, for outdoor power equipment, 11 Oz. Size, Effective to -65° F, 752-942 Stens Niteo – M3815 Stens 752-942 Starting Fluid
Best for: Cold, damp mornings
This is an OEM-style replacement for outdoor power equipment, a good match for people who mow early in the season when temperatures are low and the engine is harder to start after rain.
Key specs
- Size: 11 oz
- Rated effective to -65°F
- Designed as a replacement for Gunk M3815
Pros
- Low-temperature rating suits early spring starts
- Replacement for a widely used original part number
- Works across a range of outdoor power equipment
Cons
- Generic packaging compared with name-brand cans
- Still requires careful use around hot components
Bottom line: Best suited to owners who mow in cold, wet spring weather and want a low-temperature rated option.
Blaster Chemical Lawn Mower Starter, 16 oz, Pack of 2
Blaster Chemical Lawn Mower Starter – 16 oz Starter Fluid for Small Engines – Fuel System Aid for Lawn Mower and Outdoor Power Equipment – Engine Start Spray Can – Pack of 2
Best for: Frequent use and larger mowers
The 16 oz size and two-pack format suit people with larger properties or several small-engine tools who need more starting aid on hand. It is aimed at lawn mowers and outdoor power equipment.
Key specs
- Size: 16 oz per can, pack of 2
- Marketed as a starter fluid for small engines
- Includes fuel system aid language on the listing
Pros
- Larger volume than the smaller cans in this list
- Two cans give spare supply for a season
- Labeled for lawn mowers and outdoor power equipment specifically
Cons
- Larger can takes more storage space
- Owners should check the product label for use guidance before using it on an engine with a catalytic or specialty system
Bottom line: A practical choice for owners who expect to start the engine often across a long mowing season.
Lawn Boy TRU-Start 20-inch Lawn Mower with Briggs & Stratton 140cc Engine
for Lawn Boy TRU-Start 20'' Lawn Mower with for Briggs & Stratton 140cc Engine
Best for: Lawn Boy owners
This listing is a model-specific product for a particular Lawn Boy mower family. It suits owners who want a product matched to their deck size and engine rather than a general-purpose can.
Key specs
- Deck size: 20 inches
- Engine: Briggs & Stratton 140cc
- Brand: Lawn Boy TRU-Start line
Pros
- Model-specific fit for Lawn Boy 20-inch mowers
- Matches the Briggs & Stratton 140cc engine family
- Useful when a general starting fluid is not a close match
Cons
- Narrow fit; not intended for other mower brands
- Confirm the engine and deck size before ordering
Bottom line: The right pick for Lawn Boy owners who want a product designed around their exact machine.
Buying Guide
Type of starting aid
Starting fluids are ether-based sprays meant to help an engine fire when fuel is weak or the carburetor is damp. Fuel system treatments are meant to restore or condition fuel that has degraded. A rained-on mower usually needs drying first, and a starting aid second. Check the label to see which job a product is designed for.
Good picks for this: Valvoline Starting Fluid, STA-BIL Start Your Engines!
Can size and volume
Smaller cans suit an engine that starts after one or two sprays. Larger cans make sense for frequent use or several engines. Consider how many attempts you realistically need before the mower runs cleanly.
Good picks for this: Blaster Chemical Lawn Mower Starter, STA-BIL Start Your Engines!
Temperature rating
Early-season and cold, wet mornings put more demand on a starting aid. Look for a stated low-temperature rating on the label, and be aware that manufacturers specify the temperature range for effectiveness, not a guarantee of starting in every condition.
Good picks for this: Stens 752-942 Starting Fluid, Valvoline Starting Fluid
Engine and mower compatibility
Most starting fluids are labeled for gasoline small engines, but some are specific to a brand or engine family. Confirm the engine type (2-cycle or 4-cycle) and the mower model before buying.
Good picks for this: Lawn Boy TRU-Start 20-inch replacement, STA-BIL Start Your Engines!
Storage and shelf life
Aerosol cans lose pressure over time and should be stored in a cool, dry place away from heat. Keep a small supply on the shelf rather than a large stock you may not use before the season ends.
Good picks for this: STA-BIL Start Your Engines!, Stens 752-942 Starting Fluid
Safety handling
Starting fluid is flammable. Spray only into the air intake with the engine off, keep away from open flame, sparks and hot exhaust, and never use it as a substitute for fixing an ignition or fuel problem. If you are unsure about handling or a persistent no-start condition, consult a small-engine professional.
Good picks for this: Valvoline Starting Fluid, Blaster Chemical Lawn Mower Starter
Dry-out steps that matter more than the can
A spray only helps once the basics are in place. Remove and dry the spark plug, wipe down the ignition wire and coil, drain or replace water-contaminated fuel, and let the air filter dry completely. Refer to our Troubleshooting a Lawn Mower That Won’t Start: 8 Steps to Fix It for a full sequence. Then use a starting aid to finish the job.
Good picks for this: Valvoline Starting Fluid, Lawn Boy TRU-Start 20-inch replacement
FAQ
Can a lawn mower be damaged by getting rained on?
A brief rain shower usually does not harm a mower. Problems tend to come from water left sitting in the carburetor, fuel tank or air filter, and from corrosion on electrical connections over time. Dry the mower thoroughly after it gets soaked.
How long should I wait before trying to start a mower after rain?
Let the engine, spark plug area and air filter dry for several hours, or overnight if the mower was fully soaked. Starting it immediately after rain often leads to a wet plug and a longer no-start condition.
Should I drain the gas if water got into the tank?
Yes, if you suspect water in the fuel. Water and gasoline separate, and the water sits at the bottom where it can be drawn into the carburetor. Drain the old fuel and refill with fresh fuel. Consult a small-engine technician if you are unsure how to drain the carburetor.
Is starting fluid safe to use on any mower?
Starting fluid is safe for many gasoline small engines when used as the label directs, but not every engine is suitable. Check the product label and your owner’s manual, and avoid using it on engines with specialty systems unless the manufacturer allows it.
What is the most common cause of a lawn mower that won’t start after rain?
A wet spark plug or wet ignition wire is one of the most frequent causes. Drying and replacing the spark plug if it looks fouled or corroded often solves the issue.
When should I stop trying and call a repair shop?
If the engine still will not start after drying the plug, checking the fuel and using a starting aid, or if you notice smoke, unusual noises or fuel leaks, stop and consult a qualified small-engine repair technician.
Conclusion
A lawn mower that got rained on and won’t start usually needs drying and basic service first, with a starting aid as the finishing step. For most owners, the Valvoline Starting Fluid is a dependable default. Choose the STA-BIL Start Your Engines! for light, occasional use. The Stens 752-942 Starting Fluid suits cold, damp mornings, the Blaster Chemical Lawn Mower Starter fits frequent mowing and larger mowers, and the Lawn Boy TRU-Start replacement is the right pick for a Lawn Boy 20-inch with a Briggs & Stratton 140cc engine.
Sources
- Safety guidance on handling flammable aerosol products and small-engine fuel hazards (cpsc.gov)
- General information on gasoline storage, fuel quality and related equipment care (energy.gov)
Related reading
- Yardworks Battery Lawn Mower Won't Start: 7 Causes and Fixes
- Yardman Riding Lawn Mower Won't Start: 7 Causes and Fixes
- Yardman Lawn Mower Won't Start: 8 Causes and Fixes (2026)
- Yard Machines Lawn Mower Won't Start: 7 Causes and Fixes
- Yard Machine Riding Lawn Mower Won't Start: 7 Causes and Fixes
- Yard Machine Lawn Mower 20 Inch Won't Start: 4 Best Replacement Parts Compared
About Graham Fisher
Graham Fisher is part of our editorial team and reviews and edits our lawn mowers guides, checking product details against manufacturer specifications and owner feedback.
