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Recently did an oil change on a Mountfield 140cc mower and having issues keeping it running. It starts and sounds fine, then it pops a few times, idles very slow, then stalls.
I've checked the air filter and throttle which all move fine and are clean. Fuel is new.
There's two parts the the throttle that move when you adjust the throttle lever (I don't know much about it so I'll try to describe them).
1: makes the part in the air intake move.
2: makes something turn inside the carb.
Part 2 seems to keep jumping before it stalls. As if being pushed from the inside. If I hold it still, the engine runs fine but the slightest movement and it stalls.
Any ideas? I managed to mow the lawn and it seemed better once warm but still kept stalling.
I am no mechanic but last time I had stalling issues with my mower a new diaphragm fixed it. There is not too much to the engines so may be worth checking/changing.
Is that a gasket?
Just had another look and part 1 is the choke, part 2 is the throttle housing. Both are clean and move freely but it stalls as soon as I increase throttle.
Looked inside the carb and that's clean too.
My mower has been playing up for years, I should fix it but can't be arsed. If mine starts to stall out, tilting it over to get more fuel in from the tank sorts it out again. I assume a gasket or fuel pick up pipe is the issue.
Have you tried tilting it?
This is the diaphragm I meant, it is also a gasket I guess.
https://images.app.goo.gl/wSLNESkyCob2U9oP6
Not tried tilting it so I'll try and see if it helps.
I checked the gaskets both sides of the carb and could see any leaks.
Is a fuel pick up pipe just the main fuel pipe from the tank to the carb? If so, its fine and fuel flows fine. There's another pipe that connects to the tip of the air filter but can't see where it comes from.
I had loads of trouble with mine, changed gaskets, spark plug, cleaned the carb, adjusted the springs, adjusted the cable, bought a new carb.
It would run on starter fluid. I thought I'd fixed it last summer but then started doing it again. Turned out I'd bought new fuel, left it in a hot shed rather than cool garage and it just 'went off' really quickly. Wouldn't even burn on the floor.
So recheck your fuel!
1. Sounds like the choke flap.
2. Sounds like the throttle valve.
Throttle valve is controlled via the governor, choke valve will either be via the throttle cable, or an automatic control.
If it's via the throttle cable, once the engine fires you need to move the throttle back enough so the choke opens (the final bit of travel on the throttle should require extra effort so you don't accidentally engage the choke when you increase revs)
Thanks for the advice. A few more things to check.
Are 2 stroke and 4 stroke both sensitive to bad fuel? I used the same fuel for a chainsaw and hedge trimmer this morning and they ran fine. Mixed with 2 stroke oil of course.
You didn't overfill the oil did you?
Are 2 stroke and 4 stroke both sensitive to bad fuel?
No different.
Ethanol in modern fuel absorbs moisture and causes some materials to break down/go brittle.
Unless your mower is very old I'd doubt it would be affected by the latter.
Can anyone help with mine? B&S engine. It was leaking from around the carb so I replaced the diaphragm and carb (the base on the original had warped so even with new diaphragms fitted it was still leaking). After doing this it was running really slowly (almost stalling but not quite), even with the throttle fully open. So I changed the governor springs (using genuine B&S spares) now it runs really quickly even when the throttle is fully closed off. I checked the governors and they have free movement but it looks like they are simply *too* springy and aren't allowing the regulator (?) to fully operate (if I gently push at it the revs will drop).
Is there a way of fixing this? I cannot see any way of adjusting anything and getting another set of governor springs will surely have the same issue unless I just got a bad batch?
Not having much luck. Just cleaned and rebuilt the carb. New sparkplug. New fuel. Still the same.
It starts but idles very very slow. Then goes pop and stalls. If I try to increase the revs, it dies.
Any other ideas or bin it and buy another? It's lasted 9 years.
Also checked the fuel filter and that's clean. Noticed the fuel is cloudy in the tank. Its new fuel so not sure if the tank is dirty or has something inside that's contaminating it.
It shouldn't be cloudy so that sounds like an issue to explore.
Popping sounds like an air leak, possibly after the carb as it's causing the revs to lower. Any missing or split vacuum lines
hi - I'm not sure it's any help to you but I have a Masport 200ST petrol mower with a Briggs & Stratton 450 Engine - these feature the all plastic carb - I had problems with engine revs hunting up and down and then it stalling when any revs were applied. PITA - I took the carb apart - cleaned poked and prodded etc reassembled (several times) all with no success - in the end I got one of those dodgy Chinese complete replacement carbs off ebay - about 10 quid or so.
That seemed to do the trick - revs still up and down a bit but can just about cut the lawn now without stalling. I couldn't for the life of me see what the problem was with the original carb - all the fiddly little bits and jets seemed in place and clear - so who knows ? Would have saved me a sh!tload of time if I'd just bought the ebay one up front of course...
I checked the vaccume pipe from the air filter and that looks fine.
The pop seems to happen after a few failed starts. The first attempt it would start and idle smoothly for about 10 seconds then stall. The next few attempts it would start and idle very very slow. The next attempt it would start, idle slow, pop, then stall. If I leave it for 30 mins it starts like the first attempt again.
I was surprised how clean the carb was inside. Cleaned each part and the cloth was ever so slightly yellow after. Maybe rust?
The cloudy fuel has me puzzled since I drained the tank and added fresh fuel. Maybe a little moisture was always in there. For now, I've taken the fuel tank off and left it to fully dry out. I'll re assemble tomorrow or Friday and see if it works.
Update: All fixed now. It was a bad ignition coil. Did a bit more poking around yesterday and took off/re installed the coil. Didnt have any way of testing it other than watching the plug for a spark but it must have been an intermittent fault or not working with vibrations from the engine as it sparked when I tested it. Started the mower and it ran for about 10 seconds before stalling. This time it ran much smoother so something must have moved inside the coil to make it work properly then moved again to make it stop. Couldn't get it to start again so ordered a new coil for £15 with next day delivery. Fitted this afternoon and it runs better than ever! I now suspect the coil has been bad for a while.