Briggs And Stratton 550 140cc Not starting

[BandS]

Hi All,
Just wondering if anybody could help resolve my mower issue. I have a 2.5 year old B & S 550e series140cc 2.2KW mower. Prod code: 8k12-019892
1. I transported it 1 mile in the car with the front slightly elevated (~40 degrees)
2. Cut long length grass for 2 minutes and could hear it struggling to cut grass.
3. It starting running at idle speed rather than full speed.
4. It was just about cutting the grass but I had to back off before it cut out.
5. Once it cut off, I could not restart it.
6. The pull cord now feels really stiff to pull, fine to pull when the spark plug is removed.
7. Spark plug is sparking fine, I've checked this but replaced with a brand new one.
8. The air filter is dry and looks brand new. I removed it for a few minutes and it still did not start.
9. I am using Aspen 4, 4 stroke fuel that keeps stable for 5 years. ( It does not smoke or smell!).
10. Mower now has fresh oil in, although previous oil did not look bad. Mower only used around 8 times since new.
11. Brake is removed while pulling cord, although I have not physically seen this disengaged.

Any help would be most appreciated, thanks!

 

[bertsmobile1]

Pull the rocker cover off & check that both valves go in & out
A slightly loose one could have dropped off and will cause the symptoms you describe

 

[slomo]

I transported it 1 mile in the car with the front slightly elevated (~40 degrees)

Might be flooded. Remove the plug and pull the rope several times.
times to clear out the cylinder.

Cut long length grass for 2 minutes and could hear it struggling to cut grass.

It's only a 140cc engine, as in small.

The pull cord now feels really stiff to pull, fine to pull when the spark plug is removed.

Either normal compression or cylinder flooding?

Spark plug is sparking fine, I've checked this but replaced with a brand new one.

Put the original plug back in. You said it was fine. Maybe the new plug is suspect?

The air filter is dry and looks brand new. I removed it for a few minutes and it still did not start.

Think on these you are to oil the foam filter. Check your engine manual for proper info.

Mower now has fresh oil in, although previous oil did not look bad. Mower only used around 8 times since new.

Great, keep it full at all times.

I would check the valve clearance as Bert said.

Did this all start after transporting the mower at 40 degrees?