Modern unleaded fuel loses its octane rating, albeit slowly, after 10 days in a cars fuel tank, it also leaves behind a varnish type substance as it evapourates which will ruin an old style carburettor, FI is pretty much immune to this but 6 months would have certainly degraded your petrol.
just found this....According to Shell Australia’s Technical Advice Centre Manager, Warren Scott, you can generally store fuel in a sealed container for around six months before it starts to deteriorate. This assumes it’s kept relatively cool and away from direct sunlight.
“But if the container is not properly sealed or it’s repeatedly opened, [fuel] will start to evaporate and you lose some of the light components in the fuel,” Mr Warren says.
Those light components include highly important butane. As these components are lost, the fuel loses its volatility. Mr Warren says this makes the car difficult to start.
In warm conditions, fuel is especially prone to oxidisation which causes lacquer and gums to form. As a result, the fuel turns dark in colour, loses its clarity and smells like paint stripper.
Every time you started it during the 6 months you will have 'refreshed' the air in the tank... accelerating the degradation.
Last edited by bowsider; 22-04-11 at 21:21.