Small Engines (Lawn Mowers, etc.): Lawn mower power, thick grass, filter clean

Question
I have a small gas mower.  It starts ok.  But today we were cutting thick weeds and the power dropped to where it almost wouldn't work.  It cuts fine on small grass.  But power was ok on thick grass before.  Does not surge.

Answer
Hi Raul,
Easiest things first. Is the air filter clean? Did it hit any solid object like a stump or big rock? If so, it may have sheared a flywheel key and is out of time. When not under load, does the RPM seem lower than it was? Sometimes pushing into thick weeds can bend the governor spring lever in the front of the engine on B&S Quantum engines. Look for a little tab with a small spring attached to it. If you bend it out it will increase the RPM. Other than these thing it will have to be checked out at a shop.
Thanks,
Keith