Outdoor Power Equipment and Small Engines - PLEASE HELP -- Ferris ISZ Power Loss

I need some help. I have an older Ferris ISZ 61" deck with a Kawasaki 23hp engine. What is happening is that after 5 minutes, when the engine has warmed up, of load (blades engaged) the power drops off significantly. To the point that the engine almost stalls. When I disengage the blades, the motor revs right back up. Also, the engine has developed a backfire when I back off the throttle. Here is what I have done so far:

1) Rebuilt the deck (New spindles, pulleys, spring, belt, blades)
2) Rebuilt the carburetor
3) New fuel pump
4) New battery
5) New electric clutch
6) New plugs
7) Good compression
8) New muffler
9) Good fuses
10) New fuel filter (Installed correctly)
11) New and correct air filter

From this point forward, I don't even know what to look at??

Could it be a sticking valve, dirt in the fuel system, clogged exhaust, a bad hydraulic pump????

Please HELP.

David

Sounds to me like it's not getting the fuel needed to bog into the load. You might spend some more time with the carb or put on a new one. Try choking it a little to see if that helps it take the load better. If so, the carb is the problem.

I am leaning more to carbuator issue there either main jet is clogged up a little otherwise the govener is not set up right { that is possible }

Merci,Marc