Briggs and Stratton lawnmower engine not running well

[garmcqui]

Hi all,

I have a Mountfield push mower with a Briggs and Stratton engine that isn't running well. The model number stamped onto the engine is: 10D902-0153-B1

It seems to stutter and is putting out more smoke lately, especially when the revs dip. The revs seem to fluctuate a lot, and dip a lot if I change the mower's direction (especially if I'm pushing it forwards and then pull it backwards).

I've attached a couple of brief videos so you can see what I mean. I would be very grateful if anyone in the know could take a look and advise.

Many thanks,

Gareth

 

[Burnerman]

Something to try, Gareth.
Between the white nylon carburettor and the fuel tank is a rubber diaphragm and a gasket - the purpose of this is to allow fuel to be pumped up from the tank to the base of the carburettor. This diaphragm is notorious for failure so I recommend that it is replaced - often it comes with a new gasket, but make sure you get them the same way round as they are now!
At the same time, you'll see the carb has a 'dip pipe' fixed to it, with a gauze filter on the end. Make sure this is clear. Blow all of the carb drillings clear with an aerosol of carb cleaner at the same time, and do look for any water in the fuel......the little chamber that the dip pipe locates to is the usual suspect for this.
Treat it to a new spark plug, then tip the machine back onto its handles to check there's nothing wrapped around the blade underneath. Make sure the oil isn't overfilled, too.
Best use a genuine Briggs gasket - a firm called GHS Ltd is an excellent supplier of pattern and genuine parts.
John

 

[garmcqui]

Many thanks John.

I should have said - it had bad hunting issues last summer, so I treated it to a brand new carb, gasket and diaphragm this time last year - all genuine Briggs.

It seems different this time, but I'll lost certainly have a look and give it all a clean though, thanks.

 

[Burnerman]

These are pretty basic carburettors with no adjustment - however, if it has run nicely before, then it should do again!
The diaphragms deteriorate due to ethanol in the petrol, but they should last longer than a year.
Can you move the plate to the right at all - where the larger spring fastens to?
I'm a bit confused by the smoke situation.....blue smoke means its oil burning, black smoke means excess fuel - hence my thought about checking the oil level.
John

 

[Nige F]

I may be able to help- but need help myself - The smoking could be the breather valve, I changed one and smoking stopped. BUT what do you do with a B+S engine that will start fine then when hot, just empty the grassbag and it won't go again !- leave to cool longer and it will start. Same engine as OP new carb etc. in last 6 months.

 

[Burnerman]

What the engine needs Nige is a wee bit of choke, even if the engine is steaming hot.....fuel evaporation is the issue here.
If you overdo it of course, it'll go in the huff for a few minutes and then start with a chuff of black smoke.
John

 

[Nige F]

Thanks Burnerman - it's got the bulb primer not choke so should I give it 1 pump ? When cold 3 pumps as stated on the tank and it's fine

 

[Burnerman]

By all means give it a try.....but it does squirt raw fuel into the choke so don't overdo it!
Worth some experimenting, just to see if things improve.
John

 

[Nige F]

I might buy a bottle of Briggs' fuel stabiliser - maybe they know something ( other than fuel going off over winter)

 

[Burnerman]

Personally I've never needed to use that......I leave fuel in machines after the season is over - motorbike too - and I've never had any problems with it going off at all.
I wouldn't leave it two years though!
I believe that fuel used by the USA has typically a lower octane rating than ours, but I have no knowledge of that one.
John