On Thu, 12 Sep 2013 09:09:16 +0100, John Milner wrote:

It sounds like the shaking of the tank has loosened debris of some kind,
causing a fuel-feed problem.

By fupping up the flap valves. B-)

Dismantle the carburettor and check for debris lodged in a jet or fuel
passage.

If it was running OK before I'd be very reluctant to disturb the
jets. These small engine carbs can be right beggers to set up again.
Flushing or backwashing with clean fuel ought to shift any gunk from
the very fine and delicate jets. later Having looked at the link
below, these pulsa-prime carbs are even simpler than I thought, no
adjustable jets etc.

Check and clean the filters - ...

OP says they have done that.

... there may also be one in the fuel tank.

But prehaps not that one. B-)

Check that the fuel pipe is clear, a plastic one might have reacted to
the increased alcohol content of the petrol

Most B&S engines don't have a "fuel pipe" as such the tank is bolted
to the underside of the the carb and there is a filtered pickup that
is part of the lift pump/constant level fuel chamber casting.

http://outdoorpowerinfo.com/repairs/...prime_carb.asp

Has some good images (which will confirm or otherwise my assumption
of the actual engine the OP has). The B&S website is also pretty good
with downloadable manuals etc.

Also ensure the petrol tank cap breather hole is clear.

That normally just make the engine stop after a short period of
running not hunt.

--
Cheers
Dave.