The powered lawnmower has a Briggs and Stratton engine, normally bullet-proof. A couple of weeks back the bolt holding the fuel tank to the body worked loose and the tank was wobbling. I was aware of this because the engine started to rhythmically go fast/slow. It would lose revs then pick up then lose again... continually. As this was not normal I stopped the mowing and had a look and spotted the loose tank, re-tightened the bolt and continued. The mower still drops revs and then picks up again.
I have cleaned the air filter and plug but no difference.. so what do I to do next to get it to run at a constant speed ?

Cheers

JBL

On Wed, 11 Sep 2013 16:36:15 +0200, JBL2527 wrote:

The powered lawnmower has a Briggs and Stratton engine, normally
bullet-proof. A couple of weeks back the bolt holding the fuel tank to
the body worked loose and the tank was wobbling.

Body of the engine or the underside of the carburetor?

I had similar when one of the flap valves that are formed from the
gasket between the tank and carburetor got stuck/misplaced. Suggest
you take the whole carb/tank assembly off the engine and check that
the gasket between tank and carb is in the right place and the flap
valves are OK.

--
Cheers
Dave.

On Wed, 11 Sep 2013 16:36:15 +0200, JBL2527 wrote:

The powered lawnmower has a Briggs and Stratton engine, normally
bullet-proof. A couple of weeks back the bolt holding the fuel tank to
the body worked loose and the tank was wobbling.

Body of the engine or the underside of the carburetor?

I had similar when one of the flap valves that are formed from the
gasket between the tank and carburetor got stuck/misplaced. Suggest
you take the whole carb/tank assembly off the engine and check that
the gasket between tank and carb is in the right place and the flap
valves are OK.


Or the governor links have been disrupted either by the loose tank or you
tightening it.

Mike

On 11/09/13 15:36, JBL2527 wrote:

The powered lawnmower has a Briggs and Stratton engine, normally
bullet-proof. A couple of weeks back the bolt holding the fuel tank to
the body worked loose and the tank was wobbling. I was aware of this
because the engine started to rhythmically go fast/slow. It would lose
revs then pick up then lose again... continually. As this was not normal
I stopped the mowing and had a look and spotted the loose tank,
re-tightened the bolt and continued. The mower still drops revs and then
picks up again.
I have cleaned the air filter and plug but no difference.. so what do I
to do next to get it to run at a constant speed ?

It sounds like the shaking of the tank has loosened debris of some kind,
causing a fuel-feed problem. Dismantle the carburettor and check for
debris lodged in a jet or fuel passage. Check and clean the filters -
there may also be one in the fuel tank. Check that the fuel pipe is
clear, a plastic one might have reacted to the increased alcohol content
of the petrol - this problem started to surface a little while ago on
older vehicles.

Also ensure the petrol tank cap breather hole is clear.

HTH

--
John Milner

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.

On 12/09/13 09:51, Dave Liquorice wrote:
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.

snip

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.

The filter screens look as if they will trap anything that isn't
*really* fine debris, but there are enough passages and jets where junk
could accumulate.

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.

It's well worth checking ;-)

With a problem like the OP's machine has, everything needs to be
checked, including all seals for air leaks. Don't ask me how I know this...

--
John Milner

On Wednesday, September 11, 2013 3:36:15 PM UTC+1, JBL2527 wrote:

The powered lawnmower has a Briggs and Stratton engine, normally
bullet-proof. A couple of weeks back the bolt holding the fuel tank to
the body worked loose and the tank was wobbling. I was aware of this
because the engine started to rhythmically go fast/slow. It would lose
revs then pick up then lose again... continually. As this was not normal
I stopped the mowing and had a look and spotted the loose tank,
re-tightened the bolt and continued. The mower still drops revs and then
picks up again.
I have cleaned the air filter and plug but no difference.. so what do I
to do next to get it to run at a constant speed ?
Cheers
JBL

Hunting is due to the mixture being too thin. And that problem can be caused just about anywhere between fuel tank & cylinder.


NT