Petrol Mower Making a "Throbbing" Sound

[Robert Knight]

Hi, my petrol mower is making a throbbing sound when running. It has only just started happening today. It was fine the last time I used it. It sounds like it usually sounds when it's running low on petrol. Any ideas please?

 

[Burnerman]

When the engine is running low on fuel, the revs will drop and then pick up again until it finally dies......is yours doing that?
I think you’ll have to be a little more specific here.....can you do us a video with sound?
John

 

[jj4091]

Time for a service ?

 

[Robert Knight]

When the engine is running low on fuel, the revs will drop and then pick up again until it finally dies......is yours doing that?
I think you’ll have to be a little more specific here.....can you do us a video with sound?
John

Yes that is exactly the sound it's making, even though there is plenty of petrol in it.

 

[Robert Knight]

Time for a service ?

It's 3 months old.

 

[jj4091]

It's 3 months old.

Take it back to where you bought it then

 

[Robert Knight]

Take it back to where you bought it then

Bought it online and it's a real pain to package and send back. The local STIHL dealership where I could take it as its under warranty has a 3 week waiting list.

 

[Robert Knight]

Bought it online and it's a real pain to package and send back. The local STIHL dealership where I could take it as its under warranty has a 3 week waiting list.

These things are cheaper online but a real pain if things go wrong.

 

[Burnerman]

Is this one of the RM series, orange and white colour?
If it’s only 3 months old, you risk invalidating the warranty - but give us a picture of the carburettor and we’ll show you what to do.
Is there any chance you could have introduced some water with the fuel?
John

 

[lostinthelight]

Bought it online and it's a real pain to package and send back. The local STIHL dealership where I could take it as its under warranty has a 3 week waiting list.

Try a few Stihl places but you may also come up the "extremely busy" excuse , our local dealer will tell you straight...take it where you bought it.

 

[Robert Knight]

Is this one of the RM series, orange and white colour?
If it’s only 3 months old, you risk invalidating the warranty - but give us a picture of the carburettor and we’ll show you what to do.
Is there any chance you could have introduced some water with the fuel?
John

It was left outside for an hour or so during heavy rain. Could rainwater have got into the fuel while outside in the rain? Yes RM248 Orange and White.

 

[Burnerman]

Not the best treatment but the machine could put up with it! The filler cap has a breather hole which possibly could let water in.
The float chamber may have a drain down screw, but I don’t know if you want to go down that route......depends on your confidence, I guess.

 

[Robert Knight]

Not the best treatment but the machine could put up with it! The filler cap has a breather hole which possibly could let water in.
The float chamber may have a drain down screw, but I don’t know if you want to go down that route......depends on your confidence, I guess.

Thanks. Not Ideal I know! Long story. If it's water in the fuel will it work its way out itself once the current fuel is used up by the mower? The surging is annoying but it does not impact the mowers cutting ability. And I can put up with it until it it sorts itself out.

 

[Burnerman]

If I suspect contaminated fuel, I siphon it out into a jar so I can see what’s going on.
Remember, with a mower like yours, only tip it back on its handlebar - never over on it’s side.
John