Briggs 850e runnning issues under load .

Goosep00

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Hi all ,

I currently have a Briggs 850e ( no hand throttle ) engine fitted to my lawnmower . Over the past few years my lawn which is grass upon clay has developed mostly into a tightly packed moss. Now its regular that when passing over a heavy patch of moss the engine struggles then hunts thereafter . The governor spring was bent slightly years ago to increase rpm and now those higher revs which were great on ”nice grass” is now the problem as when there’s load with the moss it does this hunting until it settles (which could be 10 mins ). Iv bent the spring position back to what would have been standard . The mower now runs fine but its quiet and underpowered for the grass and filling the box ( the original reason it was bent ) .

Is there anything I can do to get the higher revs that pack the collection box but doesn’t hunt when under load ?
Would adjusting the governor itself be an option or would I still get the same hunting but louder ?

any help would be appreciated.

ps , clay and moss is here to stay on my lawn ...

thanks
 

sgkent

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have you made sure that the air cleaner is good, and that if there is a fuel filter it is clean? Generally 3 things make a gasoline engine run - spark , compression and the fuel and air mixture.

Compression would not change under load unless something was going on like a leaky head gasket that leaked under a heavier load, then slowly stopped, or as the engine got hotter. Sometimes valves can expand a little more when hot so if they lack proper clearance the extra heat can cause expansion that causes leaking, These kinds of things can happen but are not frequent.

Spark can get weak under more compression, and load can add compression because the piston does not move as easily. That said, it would recover as soon as the load was removed.

Air to fuel needed can change under load. A poorly adjusted air to fuel mixture can be pushed over the edge to speak with additional load. A car traveling up a hill can start to surge or buck if the air cleaner or fuel filter is dirty. This would be my first suspicion.

Last, a governor has mass, and things with mass can oscillate. If the mass and spring were just right I guess one could trigger an oscillation that if at a harmonic frequency might continue. However changing that spring tension would likely have changed that frequency.

I'd be changing the air filter and fuel filter if there is one. As to moss in a lawn, it is a sign that the lawn chemistry supports it rather than grass. A soil test might tell you if that is the case. I use Waypoint Labs in Memphis Tn. A full soil test is like $20. They typically email a pdf with the results about 2 - 3 days after they get the soil. If you decide to do this post that you are going to do it and I will tell you how.
 

Goosep00

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Hi sgkent , thanks for the reply . I understand all of what your saying but I can eliminate air filter /plug/engine integrity . The mower runs 100% if the governor spring is put back to “factory“ position even over moss it runs 100%. But the mower does not fill the box with grass as it’s not generating enough draft from the blade fins to pack the box , plus the drive is pretty slow in turn as it runs of the crank via belt . Thats why the spring tab was originally bent to increase revs.

( it’s obviously me bending the spring tab thats been the problem when it comes to the moss as the engine/governor isn’t set up for that load at that rpm )

sgkent , your second to last paragraph is exactly what’s happening (when the tab is bent to improve revs ) the governor and running etc or as you put it the harmonic frequency ( the hunting ) happens after hitting a patch of thicker moss.

What I’m not sure about is ; The governor is set up just now for a standard rpm and now the spring tab is back in a standard position and it runs fine , just not efficient . Would unbolting the governor and turning it more at the engine increase the revs -in turn adjusting the spring tab at carb to match , Would this work for a higher rpm and also the stable balance of the changing grass /moss ?
 
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Goosep00

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Sorry just to add , I live where lawnmowers and garden machinery are sold limited to 96db so they are very much under what the manufacturers recommended rpm would be .
 

sgkent

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I would find out what the set RPM is for that engine and set the speed at that RPM. Normally that is around 3000 RPM but it varies based on blade tip speed. I would also make sure the blade is designed to lift and keep it sharp. Third I would de-thatch the lawn. Moss is hard to stop but it can be controlled.
 

bertsmobile1

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Get rid of that section of the lawn
Put a row of bricks or blocks around that spot toss a trailer load of sandy loam in there and pack it chockers with shallow rooted flowering annuals .
We have politicans & accountants here to make your life impossible so don't make their job easier by creating a rod for your own back
 

Goosep00

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Thanks guys , I do scarify twice a year and treat it with a moss eradicating fertiliser . The soil/clay quality is that poor it turns into a full time job just treating moss . When it’s wet and warm I’m cutting once a week which when this hunting and stop starting etc gets a bit tiresome ! I’ll look further into the suggestions . Thanks for the replies !
 
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