Generator won't start after sitting in the shed all winter — carb or something else?

Classic winter storage problem — seen it loads of times. Nine times out of ten it's the carburettor, specifically the main jet getting gummed up with varnished fuel. Petrol goes off faster than most people realise, especially the ethanol-blended stuff we get in the UK now (E10 doesn't store well at all).

First thing I'd try before pulling the carb apart:

• Drain whatever old fuel is in there completely
• Spray some carb cleaner into the air intake and try starting
• If it fires briefly then dies, the carb jet is almost certainly blocked

If that doesn't shift it, you'll need to pull the carb and soak the jet in cleaner. Small wire or a jet cleaning tool to clear the passage — don't use a drill bit, you'll enlarge the jet and ruin the fuel mixture.

Also worth checking:

• Spark plug (chuck a new one in, they're a quid)
• Air filter (mice love nesting in sheds over winter, I've found nests packed right into filters before)
• Fuel valve — make sure it's actually open and the fuel line isn't cracked or blocked

Going forward, either run the carb dry before storage or use a fuel stabiliser like Sta-Bil. I use Sta-Bil in everything that sits over winter — generator, lawnmower, the lot. Makes a massive difference.

What make/model is the genny? Some carbs are straightforward to rebuild, others are a nightmare. Honda GX engines are dead easy, some of the budget Chinese units are more fiddly but parts are cheap on eBay.

Anyone else had success with other approaches? Curious whether ultrasonic cleaners are worth it for carbs.

@NickHughes is right about the carb, but before you even go there — check the spark plug first. Takes thirty seconds and costs nothing.

I had this exact saga last March with the Honda EU22i on the narrowboat. Sat all winter, wouldn't fire. Convinced myself it was a gummed jet, had the carb half stripped before my mate pointed out the plug was utterly black and fouled.

Fresh plug, started second pull. Three hours of unnecessary work because I assumed the obvious answer.

The carb varnish issue is real — absolutely — but elimination order matters. Plug, then fuel freshness, then start dismantling carburettors.

Also worth mentioning: Briggs & Stratton engines are far more prone to this than Honda GX series in my experience. What generator have you actually got? Makes a difference to the advice.

@AngliaCamper good shout on the plug, and assuming you've covered those basics — don't overlook the fuel itself. Ethanol-blended E10 (now the UK standard pump fuel) absorbs moisture over winter storage and phases-separate in the float bowl, leaving a corrosive layer that'll wreck brass jets faster than old E5 ever did.

Before pulling the carb completely, try draining the float bowl entirely via the drain screw, then refilling with fresh fuel. Had this exact scenario with the Honda EU22i I run alongside my van conversion setup — drained it, fresh fill, fired second pull.

If you're storing seasonally, use Aspen 4 alkylate petrol — it's ethanol-free, stays stable for years, and is genuinely worth the premium for equipment that sits unused. Available at most Screwfix/HSS branches now.

After carb, plug, and fuel are ruled out, don't forget the choke — these things seize solid after a winter doing nothing, same as my enthusiasm for cooking in January.

Also worth checking:

• Oil level sensor — many Hondas and Chinese clones will refuse to start if it triggers, even with adequate oil (sensor goes faulty with age)
• Air filter — mice absolutely love nesting in shed generators, ask me how I know
• Primer bulb — cracks invisibly and won't hold pressure

If it's a Honda EU series or similar inverter genny, the carbon brushes on the AVR side can also cause no-start symptoms that feel electrical rather than mechanical.

Spent three winters troubleshooting backup power on my narrowboat before I started treating the genny with Aspen alkylate fuel for storage — not cheap, but it doesn't varnish and the carb stays spotless.

@RetiredChef all solid points from everyone above. One thing nobody's mentioned yet — pull the oil dipstick and actually check the level. Low oil triggers the low-oil shutoff on most modern gennies and they simply won't fire at all. Catches people out constantly.

Also worth checking the air filter — mine was completely blocked with mouse nest last spring 😅 no joke, little blighters had been busy all winter. Swapped it for a fresh one and she fired second pull.

If you've gone through carb, plug, fuel, choke, oil level, and air filter and still nothing — check your kill switch is actually in the run position. Sounds daft but I've stood there yanking the cord like an idiot before now.