Briggs 500E series mower engine surging

[nbpt100]

Note the engine speeds
Could not find a 500e spec sheet but I do not have access to the Briggs portal where that information is .
These are the later fixed speed engines found on mowers that do not have a throttle, just a bail.
I seriously doubt that a mower spinning at 1750 would actually cut grass.

https://www.smallenginesuppliers.com/shop/html/pages/products/briggs_vertical_shaft_engines4309.html
https://www.smallenginesuppliers.com/shop/html/pages/products/briggs_vertical_shaft_engines4299.html

Thanks for the info. I guess my inductive tach is not working properly. It does jump around a bit. I will have to dig out my optical tach and pick up the blade speed to get an accurate reading.
1750 rpm does sound pretty slow.
Thanks again for the help.