I have a kohler courage pro 26hp. Model # sv735-0016. The exhaust tube with glow red at half throttle up to full throttle under no load. I've checked for intake leaks and replaced the carburetor with a new oem replacement. I've pulled
both heads and replaced the headgaskets and relapped the valves. Put it all back together and set the valves at .004&.006 intake/exhaust. I've checked the shear key several times. I've pulled the muffler as well and let it run with just the tubes. I'm at a loss for what could be causing this!! Any help???????

 

Is it running poorly? Is the exhaust glowing bright even in daylight or are you seeing this in the dark? The pipes get very very hot, glowing red. Not usually enough to see in the day time though.