[TR] TR-6 won't run below 1500 rpm.

[drew at graybealdesign.com (Graybeal Design)]

I went out to start the 6 up and although it started kind of hard, it ran fine
for about a half mile and then decided to not run below 1500 rpm. The plugs
all look the same (light tan) and there is fuel in the float bowls. It runs
smooth and healthy above 1500 but not below. I have electronic ignition. Any
suggestions?

Thanks,
Drew Graybeal