The symptoms of stale fuel never seem to be the same 2 times in a row. Last time I had this it was a poor idle and trying to stall when pulling away. The next was a general loss of performance which was immediately fixed after I filled up.
This time it is a misfire when under medium to heavy load ie uphill or accelerate in top from lower speed.
It must depend on what has actually changed in the fuel.

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Cheers Dave.

I was thinking about this recently. I was away for 2mths and the car hadn’t been run, there was less than 1/4 of a tank, it had been warm and i expected there to be issues. However the car fired up pretty much as usual and ran ok. I do remember on one of my last runs that the station i had to use only had 95, so i put octane boost in the tank as soon as i could. So i assumed that this maybe helped.

On reading up, it is evaporation and/or moisture in the fuel that makes it stale. Evaporation makes the fuel more dense, so richer, but at the same time what evaporates off is ‘volatile octane’ so the mixture is technically leaner. I had to read this about 5 times because it didn’t make sense. I think that means more fuel is there but it doesn’t burn as well, which makes sense that the cars run bad.

I think like you suggest, assuming different chemicals evaporate at different rates, it is going to depend on what has evaporated off and how much.

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1966 Mini Deluxe - “Gabby” 34 years under restoration and counting...
1970 MGBGT
1959 MGA

Empty the tank, get some fresh 98 RON from a high-volume outlet and try again...some outlets "cut" their fuel with other stuff...

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"Show me the Mini!"

Yes, or I should just drive it more. .
The thread was more about the different ways stale fuel presents. No 2 occasions are the same. It has the potential to send us off on a wild goose chase for faults which do not exist.

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Cheers Dave.

Alot of Harley riders in the states use a fuel stabiliser to preserve fuel when they're not riding them over the winter period.. I guess that's one option, but just driving sounds like more fun