No power - spitting and sputtering

First, put in a known good spark plug, preferably a Champion or NAME BRAND.
 
Second, next to the red on/off switch is a small squarish part.  It's a low oil switch.
If it detects low oil, it'll kill spark.  They do go bad...  Un-plug it and see if it helps. 
It won't hurt anything.  YOU just have to keep an eye on the oil level.  
 
Advise back..
 
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Can you advise what type mower this is? (rider, walk behind, zero turn, etc)
 
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There should be a model # on the ENGINE itself.  Please post that..
 
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That #'s showing the entire mower, not the engine specifically:
 
https://www.ereplacementparts.com/snapper-2812523bve-7085622-125-rear-engine-rider-series-parts-c-207777_207778_208141.html 
 
There should be a model # on the engine itself..
 
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Much better..
 
Your engine, an approx 18 HP Brigs, OHV engine: 
https://www.partstree.com/models/219907-0131-e1-briggs-stratton-vertical-engine/ 
 
I would check valve clearances first, make sure their not too tight..
https://outdoorpowerinfo.com/engine_specs/briggs_valve_gaps.asp 
 
Check and see if the spark plug is too wet.  I know you changed the carb but the NIKKIs 
are known to flood...
 
If all the above is ok, within spec, you'll need to do a leak down test.
If the engine was over heated, it can blow a head gasket and/or drop 
a valve seat..
 
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