Cams in these mower engines are so small, think you are barking up the wrong tree. These are low rev Diesel like engines. Put the valves in factory spec and look elsewhere for your slow revs. As in 97% of all complaints are dirty carbs and or neglected fuel systems.
To more directly answer your question, you should never be at a low/slow 1750rpm like idle. Unless your engine is water cooled with full pressure lube and oil filter. These are not car engines. They are made to immediately go from 0 to 3600rpm all day long. Briggs states for MAX engine life and durability, run at MAX revs ALL THE TIME. At low revs you get way reduced air cooling and lubrication. Slam her at 3600 and never look back.