Mountfield mower died

I don't know whether anyone here can either offer advice or point me in the direction of someone locally who can but here goes......
I have a Mountfield petrol mower which I have had for quite a few years. It has a Briggs and Stratton engine of the following type:
BRIGGS and STRATTON HP470
Model: 10D902
Type: 0141 B1
Code: 02013155

It was working perfectly up to last Autumn. I tried to start it a week ago and it starts instantly after priming but only runs for a second or two - probably just uses the petrol injected by the primer.
I searched the web (as you do) and was led to believe the diaphragm needed replacement. I sent off for genuine carb kit (diaphragm and gasket) and changed them this morning.
It is EXACTLY the same.
The petrol is reasonably new (about October) and I have given the machine a good blow through as best as I can.
Can anyone offer any advice on what I can check next please?
In my (unscientific) mind I thought it must be a carburetor problem as it always starts perfectly after priming but just doesn't keep going - but I may be barking up the wrong tree.
Any help gratefully appreciated
DavidC

 

There could be bits in the bottom of the tank were there should be a filter and that may need cleaning also there is a vent in the cap which may not be letting air in as you use the fuel, try running it with out the cap

Also check the air filter

I was going to say dirt in the carb but you've change that so it should be ok

 

Thanks for the suggestion. In actual fact I have just come in from mowing my lawn!!
I partly stripped the carb down again and cleaned everything out (again!) re-assembled it and tried it. Just the same. But I kept on starting it using the primer and suddenly it actually kept running but really roughly. I let it run and within about 5 minutes it was running perfectly. I imagine there must have been a blockage which I hadn't spotted which slowly cleared itself.
It now starts and stops perfectly again. The test will be the next time I use it!
I will certainly check the cap to see if the vent is OK.
Thanks
DavidC

 

Your welcome, hope it helps

 

Good to hear it's going.
You will find very few walk behind mowers have an in-line filter and they have to be added on if you want one.
Normally it's rubbish that enters the carb when filling which is the main cause for blocking carbs.
Next season on the last cut run the mower dry before storing as petrol contains ethanol which breaks down in a very short period and is not good for carbs.

 

Switch off fuel supply after you have used it,and run machine till it cuts out. If you leave it with fuel it can build up a varnish in the carb and causes running problems. Modern petrol decays with age so new fuel will help.

 

Glad to hear your mower is working great now.

You mentioned the petrol is fairly new looking at the date of your post, it was 5 months old. Having sid that, I used petrol from last autum and had no problems.

Just for info - petrol nowadays contains aprrox 5% ehtanol, which is pure alcohol (the type used in alochol drinks) and it unfortunately can absorb moisture from the air, leading to a reduced effectiveness over time.

5 months may not be long enough to render your petrol ineffective but the dealership I bought my mower from suggested using an additive in petrol over winter to stop it from absorbing water content from the air. It cost about £3.00 for a bottle and so little is needed, it's enough to last a long time.

The government are set to double the ethanol content in future as part of emissions targets commitments, so it's something that may be wortwhile bearing in mind.