Dies After 45 Minutes Running

[Fnu Lnu]

Briggs and Stratton Engine 12H802-2677B1 Engine on a lawnmower starts and runs. However, after about 45 minutes of running full speed, depending upon the outside temperature, it will die and not start until it is full cooled off.

I have;
• de-carbon the head and top of the piston
• buffed the rust & corrosion off of the armature / magneto and the flywheel; gapped & reinstalled

But it ran the same.

I suspect a weak armature / magneto because the engine is 24 years old.

Am I heading in the right direction?

 

[Bertrrr]

Make sue it's not fuel related first , your tank vent possibly is plugged off , then check for fire if / when it happens again , still have fire , it's fuel related In my opinion

 

[Fnu Lnu]

I really do not believe that the issue is fuel related because the carburetor is a new OEM Briggs & Stratton, the fuel cap is clean, the fuel tank is clean and rust free (I only use real gasoline, not car gas), the in-line fuel filter is new, the air filter is new, and the spark plug is new.

The issue seems to be heat related because while mowing 1/4 acre, full throttle, during the heat of the day after about 3/4 hour or so it will die and cannot be restarted for about an hour or more of letting it cool off in the shade.

The mower was purchased new back in 2000, so it is 24 years old. However I stopped using this mower (self-propelled Snapper) back in 2017 when I bought a lawn tractor. Then last year I broke a mandrel (hidden rocks) and punctured too many holes in one of the steering tires (hidden thorns) while helping my elderly neighbor by mowing their property (no good deed shall go unpunished). So while waiting for the new parts to come in I decided to use the 23 year old Snapper on our property. That was when I experienced the "dies when hot" issue, which is why I am questioning about the possibility of the armature / magneto being weak.

 

[Bertrrr]

Coils can stop working after getting hot ,sorta rare but happens sometime , when it happens again , see if there is still a spark at the plug , if not it's probably the coil

 

[GearHead36]

the fuel cap is clean

Unless you took it apart, the vent could still be plugged. Next time it does it, remove the fuel cap, and see if that fixes it.

 

[DaveTN]

Just curious what color spark is at beginning cold and when it’s hot and quits. Does
it start to cut out and miss or lose power and die all at once?

 

[Skippydiesel]

".........the fuel tank is clean and rust free (I only use real gasoline, not car gas)"

All metal fuel tanks can/will rust.
All fuel tanks "sweat" ie condensation develops . This is especially so in climates that have a wide daily temperature range, at certain times of the year. The condensat collects in the bottom of the tank. Plastic tanks will not rust of course however metal ones will - it may take along time but nature will take its course.
The only long term preventions are:

• Drain tank regularly (at least once per season)
• Keep tanks a minimum of 75% full

Water may be worse with ethanol blends due to the hygroscopic nature of the ethanol.

 

[Fnu Lnu]

SkippyDiesel,
I really should have said that the fuel tank is plastic. I misspoke. Also, as to your comment; "Water may be worse with ethanol blends"; thus the reason that I only use real gasoline.

At the local small town source for "real gasoline"; one day last year (2023) I was buying more fuel because I had finally used up the absolute last of the fuel that I bought back in 2021. I asked the owner how long this gasoline will last, explaining that what I was currently burning (remember that this was last year) was two years old. He asked another customer, an older gentleman; "You know better than I do, how long does this gasoline last?". The old man answered; "At least seven (7) years.".

That is why anyone I am visiting with and the conversation gets around to small engines, I highly recommend that they avoid using automobile gas and then tell them of a few places where they can get the real gasoline.

Thank You for reminding me about metal fuel tanks. Of the 7 or so small engine units that I have, 2 of them have metal fuel tanks. I will be more careful about Winterizing them this year because of your advice.

 

[Fnu Lnu]

Just curious what color spark is at beginning cold and when it’s hot and quits. Does
it start to cut out and miss or lose power and die all at once?

Dave,
I have not tested the spark because when it dies I wear myself out pulling the starter rope.
It dies as if it had a "Kill Switch" or an "On / Off Switch" and someone turned the engine Off while I was mowing.

 

[DaveTN]

Dave,
I have not tested the spark because when it dies I wear myself out pulling the starter rope.
It dies as if it had a "Kill Switch" or an "On / Off Switch" and someone turned the engine Off while I was mowing.

If you’re getting good bluish white spark at beginning and end the coil should be fine. Weak
orange reddish spark means coil weak and going out. That’s why I asked about color of spark.