Fires right up cold, runs fine, then won't restart once it's warmed up — until it sits and cools, when it starts again like nothing happened. That's vapor lock: fuel boiling in the carburetor. Here's the restart that works now, and how to stop it.
Gasoline does its job as a liquid. When the engine warms up or gets switched off hot, that heat soaks into the carburetor and fuel line and can boil the fuel into vapor. A fuel pump moves liquid easily but can't move vapor, so a vapor-filled carburetor starves the engine and it won't restart. Cold, the fuel is still liquid and everything works — which is exactly why it starts first thing in the morning and quits on you an hour later. Let it cool and the vapor condenses back to liquid, and it starts again as if nothing happened. That on-when-cold, off-when-hot pattern is the signature of vapor lock.
This is a different problem from the normal warm restart, which should be easy — if yours won't warm-restart, that's the failure this guide covers. If instead your blower won't start at all, cold or hot, start with how to start a gas leaf blower. If it starts but dies at idle, see won't idle Carburetor Adjustment; if it dies when you open the throttle, see bogs down at full throttle Pull Cord Stuck.
It starts easily cold, runs, then won't restart once hot — and starts again fine after it cools. Or it gets progressively harder to start and runs rough as it heats up.
It won't start cold either, dies the moment it drops to idle, or bogs down when you hit full throttle — those are separate faults with their own guides linked above.
Vapor lock is the headline, but a few things make it worse or mimic it. Work top to bottom — the first three are cheap and cover most cases.
The main event. Engine heat boils fuel in the carburetor and line into vapor after the blower warms up or is shut off hot, and the pump can't draw vapor — so it won't restart until it cools. Stale and ethanol-blended fuel vaporize at lower temperatures, which makes it far more likely.
The fuel cap has a tiny vent that lets air in as fuel is used. When it clogs, warming fuel expands and builds pressure — or a vacuum forms — and fuel delivery goes haywire, worst when hot. The classic tell: it dies hot, you loosen the cap, and it restarts.
A warm engine doesn't need choke — it's already vaporizing fuel fine. Choke it like a cold start and you dump in too much fuel and flood it, which feels exactly like a hot-start failure but is self-inflicted. A wet spark plug and a strong gas smell point to this.
A carburetor running lean makes more heat, feeding the vapor-lock cycle. And the carburetor's metering diaphragm stiffens with age and heat, so it meters fine cold but fails once warm — the engine dies as it heats and won't restart until it cools.
These engines are air-cooled. Grass and dust packed into the cooling fins, or a carbon-blocked spark arrestor trapping exhaust heat, push running temperatures higher than designed — which is what tips a borderline blower into vapor lock and hard hot starts.
Least common, but real: a failing ignition coil can produce good spark cold and lose it once it reaches temperature, so the engine cuts out hot and won't restart until it cools. It mimics vapor lock almost exactly — the difference is it persists after you've ruled out fuel.
How it behaves when hot narrows the cause fast. Find your pattern, then confirm with the matching step above.
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| What you notice | Look first at |
|---|---|
| Starts cold, won't restart hot, fine once cooled | Vapor lock — fuel & cap |
| Cracking the fuel cap lets it restart | Blocked fuel cap vent |
| Wet plug, strong gas smell, flooded feel | Over-choked — flooding |
| Runs hotter and rougher the longer it goes | Lean carb, clogged fins/arrestor |
| Dies hot even with fresh fuel & clean cap | Carb diaphragm or ignition coil |
| Worst on hot, humid days over ~85°F | Vapor lock — switch to premix |
Most hot-start problems come down to fuel quality and a handful of cheap parts. Confirm the exact part for your model before ordering — the blower's manual or model number is the fastest route to the right fit.
Vaporizes at a higher temperature than pump gas and stays fresh — the single biggest lever against vapor lock.
Find premix →Keeps mixed fuel from going stale and vapor-prone between uses. Add it to every batch if the blower sits.
Find stabilizer →A fresh vented cap fixes the pressure/vacuum fault behind the loosen-the-cap-and-it-starts symptom.
Find the cap →Cheap insurance while you're in the tank chasing a fuel-side fault. Replace the fuel line if it's brittle.
Find the filter →Fresh diaphragms and gaskets for a carburetor that meters fine cold but fails once it's warm.
Find the kit →The fix when spark disappears only once hot — the last-resort cause after fuel and carb are ruled out.
Find the coil →Almost always vapor lock: heat boils the fuel in the carburetor into vapor, and the pump can't draw vapor to restart. It starts fine cold because the fuel is still liquid. Let it cool 10–15 minutes and it usually starts again — the lasting fixes are releasing tank pressure, using fresh non-ethanol fuel, and clearing anything that makes it run hotter than it should.
It's fuel vaporizing before it reaches the engine. Heat soaks into the carburetor and fuel line after the blower warms up or is switched off hot, boiling the fuel into bubbles the pump can't move. The engine starves and won't restart until it cools and the fuel condenses back to liquid. Ethanol-blended and stale fuel vaporize more easily, which makes it worse.
Cold, the fuel is liquid and everything works. Hot, fuel can vaporize in the carburetor, pressure can build in a poorly vented tank, and a marginal carburetor or ignition coil that's fine cold can fail at temperature. Vapor lock is by far the most common. Loosen the fuel cap after it dies hot — if it then restarts, a blocked tank vent is the cause.
Often, and it's a useful test. As fuel warms it expands and vapors build; if the cap vent is blocked, tank pressure disrupts fuel delivery. Cracking the cap releases it. If the blower restarts right after, fit a new or cleaned fuel cap with a working vent — don't just run with it loose, which lets in dirt and water.
Don't choke a warm engine — that floods it. Set the choke open, hold the throttle wide open, and pull firmly. If it's vapor-locked, prime several times to flush the vapor, crack the fuel cap, and if needed give it 10–15 minutes to cool. The full cold, warm, and flooded procedures are in how to start a gas leaf blower.