I’ve been noticing that my valve covers are starting to blister on my 440. The engine temp for the coolant is a nice 170*. When I took an infrared thermometer to the exhaust manifolds it was around 400-500* on the exhaust manifolds at idle. What are normal exhaust temps for idling? Also, the engine is not misfiring or anything. Is my carb the problem?

Thanks for the help.