John Deere 160 lossing power when mowing

[trx250r]

Hello, I have a John Deere 160 tractor with a FB460V Kawasaki. The motor runs well, and has 83 pounds of compression. But when I cut my lawn it dies right down, I have rebuilt this mower all winter long and it looks good, and runs good, but has no power under a load. If anyone has any ideas I would greatly apreciate them. Thanks -Walter

 

[trx250r]

Also the exhaust sounds louder under a load.