Why does your riding mower backfire and lose power when you engage the blades?

It sounds like your enigne needs a tune up. An engine that is not running as strong as it should will have little effect while running without the blades engaged. Once you engge the blades and put that extra strain on the engine it will show that there is something wrong.

You can start with just a new set of spark plugs. You might get by with just replacing them. If not, you may have to have a mechanic look at it for carburetor cleaning, carb adjusting, coil cleaning or replacement...