My buddy just bought a t-1 engine, (1973, DP 1600, full compliment of 
emmissions junk), and found somthing that neither of us is 
familiar with (perhaps because we try to stay pre-'68 in our 
seemingly neverending quest to avoid Utah's emissions restrictions 
on simple to maintain and diagnose powerplants).  There's a line 
leading from the driver's side heat riser pipe to the manifold at the 
base of the carb.  I haven't seen it yet, but he says it looks stock. 
Any ideas as to what this might be?