mower running rough when hot

[r896neo]

I have a 2 month old rover mower with a B&S engine. It runs really lumpy and eventually cuts out when warm. Starting from cold its fine for 10 mins or so. Th fuel is fine as its in my other mower and i know its under warranty and the dealer will sort it but he is about an hours round trip to get there and i thought i'd ask for any ideas first in case it was something simple.

Ideas??

 

[Richard C]

Unlikely there is much wrong with the engine if it’s only 2 months old but you never know! The most obvious thing to check is the spark plug cap, HT lead & low voltage ignition coil connections/earth; otherwise it could be anything from fuel choking/starvation, ignition coil breakdown or even engine damage. Try the simple ignition checks above (clean or even buy a decent new spark plug) but other than that, don’t start messing with it or you will invalidate your warranty.

 

[Burnerman]

It sounds like the mower is running too rich, so just check the air cleaner for any contamination, and you'll probably find the spark plug sooty.
The early engines had adjustable carburettors but on yours I guess its fixed. One more thing is to check the throttle cable adjustment which often go onto the choke setting from maximum.
John

 

[r896neo]

Yea i checked the plug and if anything it looks a bit white like its running lean/hot? It's got a primer and no choke. Checked and cleaned out the air filter?

I don't really want to touch much else due to the warranty so I think a trip to the dealer is needed. Cheers anyway

 

[TicklyT]

The often forgotten air vent usually in the fuel filler cap can lead to all sorts of 'interesting' problems if it gets blocked.

 

[digdilem]

Further to the above (the air admittance valve/hole is a good start)

Ensure engine block clean from all grass cuttings, as well as any air vent holes (so air gets blown over it).

Check the fuel. Been standing for a while?

Check the plug. Should be a light biscuit colour. If white, too lean/hot. If black, too rich.

Check air filters.

Check choke operation to ensure it's releasing ok.

Check fuel lines and pipes for leaks, blockages and cracks. Also if they're touching hot parts they could be evaporating fuel if the line gets too hot, or sucking air in affecting the mixture.

If all else fails, read the manual!

In my experience, modern B&S engines are great and require very little setup or maint. Eventually plugs need cleaning.