earlyriser

I'm with Alfaholik with the idea of fuel that has aged.

I had a generator, on a carb, which had sat for about 4 months, which wouldn't start. Opened the carb bowl up, and the fuel had started to turn syrupy, and in places had gelified into icky flammable blobs.

I was surprised it had gone so far in 4 months, so six months is definetly in territory for going gloopy.

I believe it is to do with the additivies to the octane, either reacting with each other, or with the octane itself, causing polymeristation, i.e. the 8 carbon chain octane starts becoming 10,12,14,16 etc carbons. As the number of carbons on the chain increase, the more solid the result.

This is why some people claim a difference in fuel quality in favour of the cheap supermarket stuff. It may not have so many "trick" additives as the BP or Shell, or as much Octane (97 RON rather than 98), but the freshness from the high turnover at supermarket petrol stations off sets it "lower quality". It would be difiicult to prove this, as atmospheric affects can have as much influence (cold wet air Vs Hot dry air), but enough anecdotal evidence is about for there to be something in it.

I would consider flushing the fuel system with clean fuel, and maybe even go to the expense of having your injectors ultrasonically cleaned, or at least checked. They have very fine holes through which the fuel flows, which would clog very easily, even at the very high fuel rail pressures.