I have a 25 year old Briggs and Stratton engine that I'm using on a slightly newer frame. I basically put this mower together myself from scratch. I junked the air filter and removed the governor. I have manual control over the throttle just like a weedeater. Once you get used to manual control, there's no going back to having a governor to control the throttle. The engine still runs like a champ. The cylinder looks pretty damn good last time I pulled the head.

Anyway. I was mowing the lawn and I ran out of gas and didn't have the money to get more gas. So, since I had a little bit left to do, I decided to put in some charcoal lighter fluid in the gas tank. After I put it in, it fired right up. Now with gasoline in the tank, if I jam the throttle wide open from idle, the engine stalls. But with lighter fluid, if I jam the throttle wide open, I get an instant response. Now this is unbelievable! It seems to rev higher with lighter fluid too. One drawback I have though is that the torque seems to be lower. If I bog it down in the grass, it'll start knocking and smoking until it stalls.

Interesting.
I used to have a 21 inch Sears 5 hp self powered mower. (with the "Eager Beaver" engine!! )

It would not cut so well in longer grass so I wired the governer open and used a hand throttle. It cut much better, but after 1 1/2 seasons the engine threw the rod through the side.

These Briggs engines will rev much higher and produce bags more power without a governer, but they will not last too long.

I also have an 8 hp riding mower. (Tecumseh engine) I couldn't find a carb rebuild kit, so I tossed it and bolted on an old carb from my Honda XR185 dirt bike. Lots more power, and so long as I dont rev it like mad it seems to run fine.