How do I get more power from a 4 cycle push behind mower?

Turbo! Nitrus! Cold-air intake! Headers!

But really.. sometimes you can adjust the tension on the governor spring to squeeze a little more out of it. This just keeps it running closer to it's maximum all the time, it doesn't increase the maximum. But it can be enough to get you through a spot of tough grass sometimes.

The downsides? You'll use more gas, it'll be noisier, and the mower will die sooner. At which time you'll just do the simplest thing; buy a bigger one.

i do not think that a 7 year old mower will give you the power that you expect. by the way, why do you want so much power? i am a gardener and have no problem with a 6.5-7.0 mower. if you really need more power, buy a commercial use honda lawn mower. when you know the price, you might think about keeping the one you have, $1000-$2000. remember that mowing the lawn too short is bad, so your mower should be good enough if you mow it high.

Go to the Briggs racing site and check it out. It is probably a bit expensive for a lawn mower. I am not sure what you think can be done to get 2hp increase. Changing cams, boring, racing pistons etc can be done but like I said, costly.

drop it off a bridge and get yourself a push mower