Wondered if anyone could diagnose an engine problem… It’s a Hayter Spirit mower – 4 stroke petrol engine, pretty basic.

When I use it, it will run fine for ~5 mins, then for no apparent reason it will idle really roughly and at ~10% revs. After ~2 mins of really rich smoke puffing out it will just kick back to life and full revs again.

When I looked at the spark plug it’s really black. I have changed this but it just ended up oily again. I have changed the oil but still no improvement. The oil level isn’t too high.

Here is an exciting video of it when it is in ‘rough running mode’. For some reason in the vid at the end I tipped it up which seemed to improve things but normally if you just let it run rough for 2 mins it starts up again.

[video]http://www.youtube.com/watch?v=qv41ENoywcg[/video]

Any thoughts? Maybe it needs a new Johnson rod? I looked under the black plastic cover to see if there was any sort of “Run well” switch that might have flicked to ‘Off’, but there wasn’t.

Sticking choke?

old fuel?

Unlikely to be the fuel I guess if it’s running ish. Sticky choke sounds likely. Have you tried revving it manually directly from the carb throttle rather than via. the throttle cable, giving it more beans than the throttle cable and flywheel governor allow normally for a while might help … cleaned the air and any fuel filters?

I would strip the carb and give it all a good clean, could be a blockage but it sounds like it’s overfilling not running lean. Then have a stare at the choke- does yours have a manual choke? Is the cable adjusted ok?

Have a look at the crancase breather as well – can’t remember where it is on these though. If you’re near Warwick you can swap bits out with a spare scrap engine I have if you need to.

Yeah I read that can be a common cause so have replaced the fuel completely with fresh.

Could be sticking choke. Something to do with the governor, or maybe just something wrong with the carburettor, really not sure.

It’s strange how it just dies, runs badly for 2 mins then just picks up back to full revs of its own accord…

Is the plug black with oil or with soot? If it’s soot then the fuel/air mixture is too rich, that is there’s too much petrol in it. There may also be petrol on the plug, if the plug’s wet sniff it to check if it’s oil or petrol. Choke could be sticking as said, and/or the carb could probably do with a strip down and clean.

If it’s oil on the plug then you probably have worn piston rings and sump oil is getting into the combustion chamber.

TBH I’d start with checking the choke cable is not getting stuck and spray carb cleaner in the carb. Unless it’s a very old and abused engine, I doubt it’d be worn rings,

How old is the mower?

a friend has a hayter mower that he bought last year that has the same symptoms. He sent it back under warranty where they replaced the carburettor. They said that they had had a few fail like this in the last 12 months or so.

My hayter mower (7 years old) has run fine since I bought it.

If it is recurring then has the ring of temperature related problem to me, time to heat up at full chat which then heat sinks to other parts then cools off whilst running rough and excess fuel(has a cooling effect, lowers combustion temperature). Symptom is definitely overfuelling, nothing to do with fuel itself IMO, need to check if the heating up is causing sticking parts or something (choke). You definitely want to take carb off and clean it thoroughly.

Thanks for the advice – might be worth trying Hayter first. If no joy with them I will try cleaning the carb. Will try and find a vid online of how to do that, I have the bad feeling that I will try and springs will fly out everywhere then I’ll have to just throw it away 🙁

It’s relatively new, I bought it last year but can’t easily get back to the shop so would have to try Hayter direct.

The temperature comment is interesting – that’s exactly what happens. Turning engine off and back on doesn’t affect it at all, just time, so temperature related is likely.

The float is sticking in the float chamber and flooding the engine with fuel. Clean out the chamber and the little needle valve, which sits on a tab on top of the float – a little like the ballcock in your water tank at home.

Does it keep doing it every 5 mins? Or just once?

It does it repeatedly and more frequently after the first time.

I’ve grown to hate the mower. I just wanted a simple petrol mower. I wanted to cut the grass and go, now I feel emasculated by it. My other half listens to my complaints politely but I can tell she thinks less of me as a man due to this.

I’ve grown to hate the mower. I just wanted a simple petrol mower. I wanted to cut the grass and go, now I feel emasculated by it. My other half listens to my complaints politely but I can tell she thinks less of me as a man due to this.

Yea, sorry but you need to MTF and conquer that mower, show its who’s boss, don’t let it win. Even if that involves thashing it with a tree branch and then taking it down the tip in favoour of a new, obedient one. That’ll learn it, and show your missus that you are a healthy chest beating alpha male.

If you keep tipping it up you might actually BE emasculated by it 🙂

Clean the carb.

A consumable item on all the B&S engines I’ve got is the carb diaphragm, they split. Symptoms are usually uneven running speed, but worth bearing in mind once you’ve got the carb apart.

Take it apart, be a man!!

Air filter off, undo 2 bolts and it will fall off (empty the petrol tank first as it’s gravity fed and will piss everywhere).

Take it apart (there’s only a couple of bolts/screws), and clean it all up. Put it back together (replace any split gaskets etc, have a look on ebay for carb rebuild kits – you’ll probably get one for a few quid), put fresh fuel in and fire the baby up.

Then scratch your head for a bit (after you’ve washed your hands obviously – they’ll stink of fuel). Then come back on here and ask the same question again, but at least you will have ruled the carb out! Sparks next!!

Bought some carb cleaning spray and a new plug from Halfords last night. Changed the plug, took the air filter off and gave the inlet a good spray. The corrosive liquid rebounded straight into my face. I couldn’t tell if it was tears of sadness or just the caustic cleaning fluids burning my eyeball but either way it hurt.

Still runs badly and did the same thing. The new plug got sooted straight up as well so I’m looking up which is the correct rebuild kit now and will get one ordered, then will take the carb apart. The float valve sounds a likely candidate I think.

I won’t let this defeat me!