Briggs and Stratton surging

I have a Briggs and Stratton engine on my riding mower that surges at full throttle and does not run at any lower speed. It seems to be fine when the blades are engaged.  I've changed the carb, fuel filter, governor springs, fuel, and spark plug. Not sure what do do next.

A MODEL # for the engine would help.
 
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31r9070062g1

Did this issue just arise, (used to run fine), been sitting for awhile with e fuel in it?
 
What you describe is a fuel related issue.  I gather you put on an aftermarket carb.
That, I would remove and go thru the original carb.  All orifices and jets must be clear.
 
Make sure fuel is getting to the carb(good flow) and that the solenoid, on the bottom of the carb
is fully retracting with key on (12 volts to it).  That solenoid STOPS fuel from flowing when you loose 
12 volts...    I'll often cut the needle off, disabling it altogether.  It's supposed to stop back firing. 
Removing the needle won't hurt anything..
 
Here's your engine in general:
https://www.jackssmallengines.com/jacks-parts-lookup/manufacturer/briggs-stratton/briggs-stratton-engine/200000-399999-series/31r900-to-31r999/31r907-0062-g1 
 
 
Here's you carb:
https://www.jackssmallengines.com/jacks-parts-lookup/manufacturer/briggs-stratton/briggs-stratton-engine/200000-399999-series/31r900-to-31r999/31r907-0062-g1/carburetor-and-fuel-supply-group
 
Part #147 is your pilot jet.  Has this been pulled and checked (main jet as well)?