I remember when I was a kid that heat riser problems were a common cause of poor engine performance, especially in winter when they were stuck open.
I guess I AM lucky because it doesn't cause me any problems. I remember as a kid that most of the heat riser problems I heard about were from too much noise. Just this morning I fired her up & let her warm up because the weather's been too bad to take her out for a drive. Other than cranking a bit slow because of the cold oil she lit right up & ran fine.
