Dave Liquorice wrote:
Do you know how old that fuel is? Unleaded goes "off" if stored for afew
months in a non-vapour proof container. Many cheap plastic petrol "cans"
aren't particulary vapour proof.

No I don't. It's probably worth replacing it anyway. Would it be safe to
put the excess in the car? (Otherwise I can't think how I'd dispose of it)

With a few priming pumps I can get it to run for about 1-3 seconds
before it dies.

Could be blocked jet(s), filter or passageways within the carb.

I probably need some oil in there... what oil and what ratio? I'm
guessing it's two stroke since it's pretty basic - but how do I check?

Is there a oil filler/dipstick anywhere. My guess for a lawnmower engine
to be a four stroke unless it's *very* old.

Will I have damaged anything by running it without oil?

Look for that dipstick and see if you have run it without oil...

OK, will do. I didn't see any oil filler or dipstick on the top - possibly
there's something accessible from the side/underneath that I've missed.

Has it a manual choke?

Not a manual choke as seen on a car (or if there is I haven't spotted it).
There's a throttle lever which has 'on' and 'off' but it's cable-linked so
it's possible to throttle it back a bit. I'm not sure that would be
possible in the 1-3s before it dies.

Firstly I'd check the oil level (but that is probably OK) then take the
plug out and check it's appearance, condition and gap. Next have a look
at the carb and fuel filter and swap the old fuel for fresh.

Right, will have a look as soon as I get a chance.

Thanks for the advice,
Theo