Small Engines (Lawn Mowers, etc.): Honda, riding lawnmower, carborator

Question
I have a Honda HT4213 riding lawnmower that loses power. It runs good when first started up and as soon as I engage the mower it starts to bog down. If it's good after I engage mower, then as soon as I put it into gear it bogs down. I checked timing, plugs, fly wheel, drag or bad bearings on deck. On the carborator the needle valve you can adjust doesn't seem to do anything. Like I said it sounds great when running by it's self and I adjust the needle valve screw it doesn't change the engines performance. Any Help?

Answer
there could be two things here that it could be one that I would think it is without looking at it is a safety switch somewhere is bad or a wire that is only if the engine runs perfect before you engage anything and the other thing that I would guess is that maybe you need a valve job thanks let me know