V TWIN 18HP Brigs with ohv on each cylinder misfire only under heavy load

I have the 18hp v twin on my zero turn cub and I can run around with it and it wont miss, but once I turn the mower on it is lacking power and misfires. I have compression checked each cylinder and each were around 160psi Just for kicks I opened up both overhead valve covers inspecting the springs and rotating the motor slowly to make sure everything was moving and smooth. I have check the spark on each side and found them to be putting out spark although I did notice that one side had a weaker orange spark verses a nice blue spark. I have run sea foam through the carb. I also took my temp gun and shot the exhaust pipes going into the muffler. I did have one side over 300 degrees hotter than the other after a little bit of run time. I have also sprayed carb cleaner by the cylinder to intake off of the carb connection at idle to see if there was a surge meaning the gasket was cracked and leaking. Any other suggestions that I may be missing here?

first start by pulling the blower housing off of the engine, and make sure the gap between the flywheel and the ignition module is within the .010-.014. After that you may have to install an inline spark tester and check the spark under load. Maybe ignition module cutting out under load. Or possibly just a plug cutting out under load.

Have you tried adding a little choke to see if that makes a difference? Also might disconnect BOTH kill wires from the base of each coil and see if that makes a difference.

Strongly suggest you post engine model number when asking advice.

Walt Conner

Check for a pack rat nest under the shroud. 300 degrees exhaust temperature differential is not good.

Agree with Senior, different combustion temps. Read plug colors.