[Flatcat]

Hi all just needing a bit of advice

Our Mountfiled HP Petrol mower with the classic Briggs engine (year 2006) is starteing to sound rough.

It has the red primer bulb, and a long while ago it was about 8 pumps, and at the most two pulls. It then got to 10 pumps and 2-3 pulls, and it is now 14 pumps and about 15-16 pulls.

It also bellows out black smoke when it starts, but this soon clears. We have to make sure the windows and doors are shut otherwise it soon gets in!

We had it serviced about 3 years ago, and it has only come out and poodled round our small patch of lawn every 2 weeks in the mowing season since when we bought it.

I'm guessing its not sounding good? As with others on here, we have suffered from the poor quality build of the Mountfield ie the wheels, handle etc, and in this time I have already had to paint the underside as it had gone rusty when I never even cut the grass wet!

I don't think we should spend any more money on this one, and we went down to the mower shop this afternoon where we looked at a Viking MB 248 which seems good that we might get to replace it (anyone had experience with this mower)

Thanks

[Gwiz]

It's the standard diaphragm problem. The carb and tank need to be removed, disassembled, cleaned, and a new diaphragm put in.
I believe they're about £2.50


Edit (now fully awake)
As for the Viking, We sell those. I've not had one come back under warranty ever, but it does have the same engine as the one you have already so the diaphragm will eventually need replacing.
A lawnmower shop will charge you about 3/4 to one hours labour + parts + Vat to do the job.

[Dopey113]

Wouldn't hurt to check the gap on the spark pug, and give it a good clean, if when you pull it out its full of black soot, then that could be a problem as well

[Flatcat]

Hi all

Step dad has said we aren't allowed to buy a new mower unless we have tried fixing the old one first

Ok ive taken the carb and tank off and removed the diaphragm, although it is in very good condition, infact almost new as it wasnt replaced all that long ago. Could it still be at fault?

The spark plug will have to wait for once I have room to get to the front of the engine which I can't at the moment as there is so much stuff in the shed

[Gwiz]

From the discription you gave it sounds like a diaphragm fault to me. Look also at the pick up tube filter to see if it is blocked, thease are the most common problems on this engine.
Nowadays, you hardly ever get problems with sparkplugs, but they are worth checking, Just in case,  sometimes they can get a bit of carbon that shorts out the electrode.

[Flatcat]

thanks Gwiz

A fellow member sent me a link to a youtube video which shows someone changing that gasket, and there can be little signs of damage apart from slight warping of the gasket/diaphragm, so I will get new ones and see how it goes

Is this diaphragm going to keep need replacing every year or so? Is it a known fault?

[Gwiz]

I replace them in every service. I wouldn't say it was a Fault" as it is a service part and very cheap. Sometimes they will last for a year, other times for 5 years. There are a hundred reasons why they give out. Old fuel? petrol stored in the tank over winter? not using a fuel additive? Storage conditions of the machine when not in use?......

[Flatcat]

We never really bother servicing as this mower and engine is seen as 'disposable' in my eyes, as a new machine costs, say £250, and a yearly service cost us £75. With the build quality of the rest of the machine, it probably wouldnt last as long as the engine, so would be a waste of time, just keep the engine for spares and chuck the mower

The petrol we've been using is about a year old, so that might be why it struggles to start sometimes.

The record though was with our chainsaw which started on the 4th pull after sitting unused with 2 year old mix in it

[Gwiz]

I think you have answered why you are having problems.
1) Machine not serviced (no new diaphragm/plug etc)
2) old petrol.

Petrol has changed considerably over the last few years. That which you buy and put in your car isn't really supposed to stay in it for a year or two. Also, when petrol is stored in bulk (gallons at a time) it tends to stay fresher for longer. A small amount kept in a machine or even a gallon can, stores differently.

All I can say is that a huge amount of the work that I do involves draining out stale fuel, cleaning carburettors, removing smelly, gummy deposits from the fuel systems of all types of machinery because the owners have left fuel in them for several weeks/months/years. Hope your machine roars into life with a new diaphragm and a carb clean also!

[Flatcat]

Replaced the diaphragm this afternnon, and the engine runs a lot sweeter.

Still have problems starting, and instead of the black smoke it is now 1 plume of white smoke that puffs out upon starting, but soon clears. There is about 50% more oil above the full mark, so I pressumed it would puff white smoke all the time? Our ride on mower used to continually puff out white as that was always overfilled.

I must say though, that the engine does run nicely and sounds like it has more 'umpf' to it now

[smud6ie]

Over filling the oil does no good at all as is imposes extra drag causing loss of power,the extra agitation mixes air with the oil which reduces its lubricating properties.
smud6ie

[Gwiz]

Pressure when the piston travels backwards after combustion, will force the oil past the piston rings. You will do the engine no favour from having it overfilled.
Drain some out! :blink:

[Flatcat]

Right, after a very long delay I have finally finished the mower

I have now:

 -Replaced carb gasket and diaphragm

 -Drained the fuel tank and cleaned it out (ready for new fuel)

 -Blown carb through with air line

 - Removed 1/4 pint of oil that shouldn't have been in there (now comfortably on the 'full' line)

Thanks for everyones help

We will get some new fuel soon, and this should have saved us from buying a new mower (hopefully the engine will survive from the overfilled oil)

Damon