How long should modern petrol keep ?

I keep fuel far longer than that for mower ,compressor, generator etc. without problems.Two strokes are different,if you dont drain the carbs,the fuel evaporates, leaving oil to block the jets.I suspect your fuel has gone leaving oil in your carbies. A whiff of starting spray will start an oily two stroke,and will certainly start your bike. Your additive may be more sticky than 2s oil. Regards John.

Previously wrote:

Hello - all - not specific to Commandos but can I ask opinions as to how long modern fuel keeps in the bikes tank. Yesterday I went to start my 920 (fitted with new Amal Mk1s) and it totally refused to fire at-all. I last used it about two months ago and it ran beautifully - It had just been filled with Shell Optimax + a splash of Castrol Valvemaster+.

Both carbs fllooded (tickled) OK and I checked and was getting really good sparks on both (clean) plugs. I can only think that the dreaded ethanol has done it's worst - - .

Cheers.

Hi Mark re your fuel problem i have found this ,fuel in carbs,ie alloy can kill our fuel.

but in our tanks,steel or fibreglass is OK so switch off your taps run your carbs down,and cure the problem..

Cheers

Petrol is evil and must be burnt as soon as possible!

More sensibly; I have left bikes standing for longer but the 'Extra' fuels tend to have a lot of volatile aromatics and aliphatics that evaproate quite quickly when left in a vessel with a relatively large surface area compared with their volume. The base fuel left doesn't burn so well. In a vessel with a small surface area to volume then the problem seems to be less acute. As others have said: drain the carbs and then it should run fine.

As an aside there are anecdotal reports that the 'Extra' fuels interact badly with aluminium and associated alloys leading to the sort of problems that your've had. Then again there are anectal reports that standard unleaded will do the same if left long enough ... as I said petrol is evil and should be burnt as soon as possible.