Mountfield ride-on lawnmower stalling

[Alantro]

Hi,

My ride-on lawn mower keeps stalling this year. It runs for about 15 mins when I start from cold before stalling and then when I restart, it will only run for a few mins before stalling again, with or without blades engaged.

So far I have:

• Put in fresh fuel
• Replaced the fuel cap
• Replaced the air filter
• Replaced the fuel filter
• Stripped down and cleaned the carb
• Replaced the spark plug

I'm starting to run out of ideas, can anyone suggest anything else I can look at?

TIA!

Lawn mower is a Mountfield 1538-SD, about 3 years old.

 

[Harry Bloomfield]

Possible blocked breather of the fuel tank cap. Air cannot get in fast enough, so it is starved of fuel. Once air leak in, it will run once more.

 

[Alantro]

Thanks, I have already replaced the cap with a brand new one but no improvement

 

[Burnerman]

If the machine can run for a genuine 15 minutes (at high rpm) you might expect the fuel supply to be ok.....
If you disconnect the fuel pipe into the carb after the filter, how is the flow?
Are you using a genuine Briggs filter, or an after market paper one?
John

 

[Alantro]

Proper new filter, same as the original one. Just double checked, the flow seems fine.

 

[Harry Bloomfield]

Thanks, I have already replaced the cap with a brand new one but no improvement

Not unknown for new parts to have a similar fault. When it stops, try losening the fuel cap, is there an hiss?

 

[Harry Bloomfield]

Might it be over heating and partlially seizing? When it stops, will it turn over freely?

 

[Burnerman]

Will the engine continue to run with the fuel cap off?
One more thing.....does the engine have a low oil alert? Disconnect it if it has, for a while.
John

 

[Harveygone]

I have a similar problem that has yet to be resolved. I suspect that air is getting into a fuel pipe when the engine gets hot. If I leave the mower just a few minutes fuel fills the fuel filter housing and the mower works. When the mower stalls there is air but no fuel in the fuel filter. I am considering changing the two fuel lines

 

[Harry Bloomfield]

Gravity fed, means that if air were getting via the fuel pipe, it would suggest fuel will also be leaking out. The air is getting via the fuel tank, or being sucked up from the carb. - that would suggest a vacuum in the pipe or tank. Try releasing the fuel cap, to admit air - does fuel then fill the pipe?

 

[Burnerman]

I have a similar problem that has yet to be resolved. I suspect that air is getting into a fuel pipe when the engine gets hot. If I leave the mower just a few minutes fuel fills the fuel filter housing and the mower works. When the mower stalls there is air but no fuel in the fuel filter. I am considering changing the two fuel lines

You don't tell us which machine this is, but not all machines like a conical, clear plastic fuel filter (believe me, this is fact) so only use a Briggs red filter and see what happens.
John

 

[Harveygone]

Sorry, it's the 1436H. It had a full service last week including new plug and fuel filter. Prior to the service the mower would run for about 30 mins but once it got hot would cut out. I used the mower for the first time post service late afternoon today. After about 30 minutes the engine cut out. This was not due to it being too hot and the thermal cut-out kicking in. I checked the fuel filter immediately the mower cut out and it had little fuel in it. Fuel was however rapidly filling the filter. Once the filter was full of fuel the mower worked until the fuel filter again was empty of fuel and full of air. Whilst I was waiting for the filter to fill with fuel, air bubbles were released into the fuel tank. This leads me to suspect that air is getting into the fuel line when the engine is hot. Possibly via a small hole in one of the two fuel lines or via the fuel valve

 

[Burnerman]

The 1436H should have the standard Briggs red filter which you can't see in to - I do suspect you have an aftermarket filter fitted and I'd replace it with an original one.
30 minutes is a long run time really so I wouldn't expect any other issues, especially as you have a new plug fitted.
Would your machine have the 13.5 hp Briggs side valve engine, and no electric clutch for the blades?
Sorry I don't know what you mean concerning a 'thermal cut out'?
John