lawn mower engine cutting out

a_ominous

Not sure if this is the place, but it is a motor of sorts.
GFs father cutting grass last week. Petrol lawn mower usually cuts out after 30 minutes vutting (it is a _big_ garden). Usual remedy is to remove spark plug, clean it and put it in the oven to dry out.
Now AFAIK black soot on the plug means air/fuel mix is too rich which is either too much petrol or too little air. The mower had been serviced at the beginning of the summer. I believe the petrol is supposed to be removed each winter. It wasn't. Why should petrol be removed?

Any suggestions as to why an engine would cut out like this? Blocked carbs? How are carbs supposed to be cleaned?

TIA

peterk19

What type of engine is on the lawn mower is it a briggs and stratton or is it a Tecumsa(Fiat) if its a Briggs and stratton it sounds like the carb needs a new Diaghram if its a Fiat the carb will need a new Venturi you could try putting loads of carb cleaner straight into the carb.
The reason to remove petrol for the winter is basicly petrol can go stale and you would be lucky to get the engine to start if it was in it that and there is plastics disolved in petrols tanks and they start to solidify in the eye of the venturi when the petrol goes stale so it get more restrictive till its blocked and no petrol can get through
Pete
ps. yea it sound like the engine is running rich they only have 1 mixture screw so they are easy to tune .

a_ominous

Don't know the make, but I'll check it out later. I only remember it's a big yellow one
Will see if I can get some carb cleaner and perhaps a manual for mower when I know make + model.
tnx

fletch

a_ominous wrote:

Why should petrol be removed?

The petrol goes stale over the winter so when you fire the lawnmower up the next Spring/Summer, it prob wont start but if it does will be running on bad petrol which could potentially damage the engine.

fletch

peterk19 wrote:

The reason to remove petrol for the winter is basicly petrol can go stale.... .

Sorry missed that...anyways

KoNiT

You didn't mention the air filter, did you clean it?
If its blocked up then your mixture will be rich

rander00

Buy a new spark plug??

mike65

I'm going to leave this here for another day and if no one can help here I'll then boot this over to Gardening/DIY

Mike.

a_ominous

Have been told it's a Briggs & Stratton engine, so will see if I can clean or replace the diaphragm as Peter K suggested. Or get it thoroughly serviced.

New spark plug: been there. Works for a short while but that doesn't fix the problem, only treating a side-effect.

Mailman

If the spark plug is fouling then engine is worn out and burning oil unless it is a two stroke ingine in which case you need to change the type of two stroke mix you are using.

If it cuts out after a couple of minutes it might be water in the carb which might involve removing the tank and taking out the carb pick-ups and cleaning them or unscrewing the carb bowl to let the water drain away(dependent on model).

If it is due to ignition first thing to try is spark plug from another similar lawnmower engine and after that it might be that the electronic ignition is breaking down but this would be rare and probably covered by a multi-year warranty.

peterk19

I know the Briggs and stratton engines its the Diaghram thats gone they use a vacum system to pump the fuel into the engine and not a gravity flow system so no bowl this happens because the Diaghram is only a thin plastic material that is constantly moving up and down eventually tearing and allows too much fuel and air into the engine they usually run okish for sometime till the hole gets too big
Just bring it in somewhere for a sevice and ell them to pay partiular attentino to the diaghram in the carb
Pete

Mailman

Most modern B&S engines have a bowl type carb unless it was a very cheap lawnmower in which case it will have an older type engine with diaphragm type carb.

mike65

Moved.

Mike.