Stale fuel and a gummed carburetor cause the overwhelming majority of post-storage no-starts. Here's how to diagnose your exact problem in under five minutes — and fix it before the first storm hits.
A snow blower that ran perfectly last March can be completely dead when you pull it out in November. The reason is almost never a major mechanical failure — it's the chemistry of gasoline sitting in a sealed system for six months.
Gasoline starts to degrade in as little as 30 days. By the time summer is over, fuel left in the tank has oxidized into a varnish-like residue that coats the tiny passages inside the carburetor. Those passages are narrow by design — measured in thousandths of an inch — and it doesn't take much deposit buildup to restrict or completely block fuel flow to the engine.
The six causes below account for nearly every post-storage no-start. They're ordered by frequency — work through them in this order and you'll solve it faster.
Gas degrades after 30 days. Six months of storage leaves varnish throughout the fuel system. Most common cause by a wide margin.
Varnish from old fuel clogs the carburetor's jets and passages. Engine cranks but won't fire, or fires briefly and dies.
Carbon deposits build up on the electrode over time, preventing reliable ignition. Often found alongside a fuel problem.
The engine won't turn over if the key isn't seated or the bail lever isn't fully engaged. Easy to overlook after months of storage.
A clogged air filter starves combustion air. On electric-start or battery models, cold-drained batteries prevent starting entirely.
Low compression, damaged recoil starter, or electrical fault. Rare — and only likely after ruling out the fuel causes above.
Match your symptom to the most likely cause. If multiple symptoms apply, start with the fuel fix — it's the root of most problems listed here.
Work through these in sequence. Most machines are back running after Fix 1 or Fix 3. If you reach Fix 6 without resolution, the problem is likely mechanical and worth a dealer visit.
Old fuel is the most common reason a snow blower won't start after sitting. Gasoline starts to oxidize in roughly 30 days, and by the time it's been sitting since spring the compounds that make it combustible have broken down. The degraded fuel may also contain water absorbed through condensation — especially if it contained ethanol, which is hygroscopic.
A fouled or worn spark plug is the second most common cause of no-starts and is often found alongside a fuel problem. Carbon deposits from incomplete combustion coat the electrode over time, preventing reliable ignition. If the engine is cranking but not firing, and fresh fuel didn't solve it, inspect the plug before moving to carburetor work.
If you've added fresh fuel and confirmed the spark plug is good but the engine still won't sustain, the carburetor is clogged. Old fuel leaves a varnish residue in the carburetor's main jet and needle jet — both are narrow enough that even thin deposits restrict fuel flow enough to prevent the engine from running. The engine catches briefly on primed fuel, then dies when it can't draw more through the blocked passages.
A severely clogged air filter restricts combustion air enough to prevent starting or cause rough running. Snow blower air filters are relatively protected compared to lawn mowers, but after multiple seasons without replacement they can accumulate enough debris to cause problems — particularly if the machine was stored in a dusty garage or shed.
Snow blowers have multiple safety interlocks that must be properly engaged before the engine will start. After sitting in storage, it's easy to overlook one of these — and the machine will give no indication of what's wrong beyond simply refusing to start.
Electric-start gas snow blowers use a small battery (often a 12V lead-acid or lithium pack) to power the starter motor. Battery-powered snow blowers rely entirely on their battery pack. In both cases, batteries that sat uncharged through a warm summer — or that were stored in very cold conditions — may be partially or fully discharged and unable to provide starting power.
The six fixes above resolve the large majority of post-storage no-starts. If you've worked through all of them — fresh fuel, clean carb, new plug, clean air filter, confirmed safety switches, confirmed battery — and the machine still won't run, the problem is likely one of these:
A compression test below spec (typically under 90 PSI for most small engines) indicates worn rings, a damaged valve, or a scored cylinder wall. This requires machining or engine replacement.
If the pull cord has no resistance or won't retract, the recoil starter spring or pawl assembly is broken. Replaceable, but requires disassembly and small-spring dexterity that most people prefer to leave to a shop.
If fresh fuel, a new spark plug, and a confirmed good battery still produce no spark, the ignition coil or module may have failed. Diagnosable with a spark tester, but replacement is usually a shop job.
Mice nest in stored snow blowers and chew wiring harnesses, fuel lines, and even air filter housings. If you find nesting material inside the machine, have a dealer inspect before attempting to start it.
A 20-minute end-of-season routine eliminates virtually all post-storage starting problems. The investment pays off every November.
Either run the engine completely dry at season's end (fuel shutoff on, run until it stops) — or fill with fresh ethanol-free fuel plus a full-strength fuel stabilizer and run for 10 minutes to circulate it. Don't leave untreated E10 gas sitting in the system.
Replace the spark plug every spring when you put it away. It costs under $10, takes 10 minutes, and means you'll never troubleshoot a fouled plug at the start of a storm.
For electric-start models, remove the battery and store it indoors at room temperature. Check charge every 60 days and top off if needed. Lithium batteries stored fully discharged can lose capacity permanently.
Start the machine in October — before the first storm is in the forecast. If something is wrong, you have time to fix it without the pressure of an incoming snowfall. A brief pre-season run also recirculates oil and reveals any issues that developed over summer.
The most common cause is stale fuel. Gasoline starts to degrade after about 30 days, and fuel that sat in the tank all summer has likely broken down into varnish that coats the inside of the carburetor and clogs its tiny jets. Drain the old fuel completely, add fresh gas, and attempt to start. If it still won't run, the carburetor needs cleaning — the varnish has already set inside the passages.
The clearest sign is an engine that cranks but won't fire, or one that briefly catches and immediately dies. If you've added fresh fuel and confirmed the spark plug has a good spark but it still won't sustain, the carburetor is almost certainly the issue. Drain the bowl — if what comes out looks dark brown or smells varnish-like rather than normal gasoline, that confirms it. The main jet is the most commonly clogged passage; spray carb cleaner through it and look for free flow.
Starting fluid can get a reluctant engine to fire once, but it doesn't fix the underlying problem. If you spray starting fluid into the intake and the engine fires briefly then dies, the carb is your actual issue — starting fluid bypasses the fuel delivery system entirely. Repeated use of starting fluid without fixing the root cause can also wash lubricant off cylinder walls, accelerating wear. Use it as a diagnostic tool, not a fix.
Yes, if you can find it. Ethanol absorbs moisture from the air over time — a process that accelerates fuel degradation and can cause phase separation, where the ethanol and gasoline separate in the tank. Ethanol-free fuel stays viable longer in storage and is significantly less likely to cause carburetor gumming over the off-season. It's often sold as "recreational fuel" or labeled for small engines and costs more per gallon, but the reduction in starting problems is worth it for seasonal equipment.
This almost always points to a fuel delivery problem. The engine fires on the small amount of fuel primed into the cylinder but can't sustain combustion because the carburetor isn't supplying a steady flow. The most common cause is a partially clogged carburetor jet or a stuck float preventing the bowl from refilling. Clean the carburetor — specifically the main jet and bowl — and check for a fuel filter clog. If the carburetor is clean and fuel flow is confirmed, a stuck choke plate that closes off air after startup can cause the same symptom.
If you've replaced the fuel, cleaned the carburetor, replaced the spark plug, and confirmed the air filter and safety switches are all good — and it still won't start — the problem is likely mechanical: low engine compression, a failed ignition coil, or a damaged recoil starter assembly. These require specialized tools and are worth a dealer visit. Also consider a dealer if you find evidence of rodent damage inside the machine, which can affect wiring and fuel lines in ways that aren't obvious.