Petrol Mower Help / Advice

Got 2/3 of the way through cutting the lawns today and the mover revs dropped slowly and then the mower stalled.

Pull the chord and it started briefly and then immediately stopped.

Checked the air filter, clean, plenty of petrol.

I then found that if I pulled on a spring that is connected to the engine speed control that the revs would pick up. The spring seems to govern the speed, combined with the speed lever on the mower. Needing a quick 'bush fix' I tie-wrapped some of the links of the spring together which speeded up the revs but the mower revs no longer 'hunt'.

Its a Briggs and Stratton 675 engine

Any suggestions as to what the problem is ? I don't want to rely on the tie-wrap fix long term but know that our local repair centre will not be able to fit it in quickly. I'm handy with the spanners so don't mind having a go myself.

 

I would resist on increasing rpm with the spring, you could damage the mower engine as you may well increase speed of the blades and stress the poor engine out.
Check spark plug, replace if old. Check carb, should be a simple take the bell shape off the carb and clean out jet.
When you say hunt, are you saying it’s hunting ie constant change in rpm because that is a classic sign of fuel issues.
If it’s not been serviced then I would replace spark or at least clean it up and clean carb jet.

 

Thanks. I'll try both of these. The engine normally hunts a little when in use, normally when not mowing. I change the oil every year and the air filter was changed last year. Spark plug, maybe 2 years ago. The mower must be 15 years old and cuts about 1/4 acre of grass through the growing season.

I didn't want to mess about with the spring but I'm away for a week and needed to get the lawn cut so it was a case of 'needs must' for now.

I'll get some carb cleaner and strip it down when I'm back. Hopefully that will sort it out. The way it stopped could suggest that some muck was taken into the carb

 

Check the fuel cap as well, if it don't let air in when it uses petrol it may starve the mower of petrol

Check the fuel filter also

 

Although I would need more information to give a proper reply, my guess would be that the spring mentioned has stretched due to the governor "flap" being partially seized.

B&S engine speed is generally controlled by the amount of air that the fan forces through the engine to cool it. As the revs increase, more air passes. This moves a flap which is attached via the spring to the carburettor. The spring pulling or pushing governs the rpm. If I'm correct, making sure the flap is free, plus changing the spring should solve the problem.

I'm not sure if we are allowed to advertise companies on here, but I do have a good UK contact for the parts. Hes also a B&S expert, so if given the facts, would put you right.

Incidentally, "hunting" is not the correct term for the engine speed changing.

 

Briggs the old engines don’t have fuel filters and it’s easy for crap to get in. My local Hayer dealer fits them for the commercial lads when they purchase one or have them serviced.
The spring gets changed or adjusted to get more movement speed, it’s a trick some do but shortens the life of the machine. Some makes like Etesia offer a upgraded pulley system to increase movement speed on self propelled machines so that the rpm is around 3500 which it should be thus extending the life of the engine.
Normally and with the fuel we use today when you take the bell end off you will see it’s green and full on crap, this needs a good old clean as well as the jet part. A good soak in carb cleaner works but the jet needs to be spotless.
The smallest bit of rubbish will make the engine run roughly.
I would defo replace spark plug and set the gap, they cost pennies.
These areas are the most common issues on mowers. I normally run some seafoam through the petrol which helps clear out the carb but if it’s really full of muck it’s a strip job. Even running them dry at the end of season they still need a clean at the beginning of the next season.
You will also find some Briggs engines are better than others, the one on my John Deere has never ran nicely even after having it serviced. It pops and is just not that smooth where as the Hayter 48 has a better Briggs and has been quite good in the 10 years of use.

A little tip but be careful when you remove the bell section on the carb, the gasket can rip if old and will need to be replaced.
Also the spark plug will give signs of issues.

I’ve never needed to replace any of the spring workings, there are adjustments but in all my years I’ve never needed spring replacements on either Briggs or Honda and my Honda machine is a 2006 model and still runs well but is serviced yearly.
The part Sandy suggested is situated behind the air filter, some blow in carb cleaner in this part but I never have and prefer to strip. It’s the air mixture and on your old engine it is manual so it’s controlled via your handle.
Check the filter again, make sure it’s clean and just check the flap works when you have removed it. Very rare to see an issue here but just check.


Let us know how you get on. Touch wood it’s just an easy fix.

 

Thanks for the reply. The front part of the assembly is moving freely but I cant get to the back part as this is under the pull starter. The stretched spring sounds possible although the revs dropped whilst the mower was running at normal speed so I'm not sure.

Will take it apart when I'm back from holiday and have a bit more time.

 

@Liz the pot I think the carb will be due a clean as it hasn't been done since I bought the mower so it will be a bit cruddy in there I'd guess.

I cant complain. Its cost me a spark plug and an ignition coil in 15 years so pretty good going.

I have noticed that the engine now burns a little oil for the first 5 seconds when started from cold so maybe time to look at the piston rings this winter.

 

Mine puffs the old black smoke on start up, nothing but a short puff though, you could get the compression checked but at some point the cost and on going parts may push towards a new mower.
When you think most commercial lads change mowers every 3 to a max of 5 years and the work they do these little engines do well.
I’ve a day off today but my old Etesia is hammered and the dealer who are not cheap tells me the engine is like new and they just tell me to change the oil through the season as it runs daily.

What I have found is some companies do a better service and others do what they call a service but it’s just a basic whip over. The Etesia dealer strips the carb, cleans, checks rpm, safety cut out and blade stop, vibration levels, filters, new pull cord, spark, blade, rear rubber strip all pulleys and it comes back looking like new. Costs from £160 upwards, last year was £268 with parts required.
My Hayter dealership whips over, it’s never cleaned and gets a basic service and several times it’s failed soon after a service. Cost £80.

I’ve noticed Etesia have produced a new model with wheel adjustment rather than the move to a single adjust for all wheels. I’m tempted as that adjustment aids wet grass collection and again they have listened to the users unlike other manufacturers.

 

Just ordered the bits to sort the issue out. Plug, cleaner, gasket set and spring. If that doesn't fix it then its time to look for a new mower.

I noticed that my sit on mower was running a bit rough this morning when I cut the chicken paddock so that's another job on the list. I suspect that the carb will be gunked up on that as it has only had the oil changed every year and no other servicing. Its 19 years old so ready for a bit of TLC.

 

Bit of an update on the one. The parts arrived while we were on holiday. Stripped and cleaned the carb this morning. I was expecting it to be gummed up but it was clean. All cleaned through with carb cleaner. Replaced the gaskets

Re-assembled, replaced plug and spring. Started up and it was the same.

Stripped the mower further and found that there is a link from the back of the mower to the carb that appears to have some sort of flap / actuator within the engine. This was covered in grass clippings so I cleared this all away and lubricated.

No difference.

Then decided enough was enough and it was time for the old mower to be put out to grass.

Ordered a Mountfield SP555 V which seemed to suit my needs.

I may look deeper into the issue but don't have the time to mess with it right now. The old mower stands every chance of finding its way onto ebay as spares / repair

 

Thats a shame. You could always take it in for a quote for repair. Depends on how much to repair and whats gone wrong. Sadly some times the cost with age just means its come to the end of life.

 

I've got ( dad mower really ) a Mountfield SP555V its quite nice to use, handles are a bit long for my liking but manageable. The plug in shoot a poor design in my opinion when removing the box/bag the plastic cover drags the grass out of the box. The aluminium deck sounds tinny when hitting small twigs to me but I am normally used to steel line decks. Its not to good with wet / damp grass either , and the gap between the drive and the main handle is to wide even for my hands.

But in all its a nice machine to use , nice cut , reasonably quick , big wheels hardly leaves a wheel line, good engine which is on vibration mounts the engine vibrates like mad to look at.

 

I don't know how commercial guys kill a pro machine off in 3-5 years , one of the old john deere has come to the end of its life due to price of parts , that mower was made in 1997 and was out everyday doing contract work doing monthly cuts on around 40 -60 gardens per day , its had a easier life over the past years but still works but when coils are £150 plus other parts its time to let the old deere go

 

They abuse them, make lots of money and simply replace them.
The Deeres are (pedestrian) Sabo mowers, german made.