Engines NEED that exhaust heat to keep the mixture uniform- - - -all the time- - - - -it's not just a warm-up thing. Once the heat riser valve opens up the flow is reduced drastically, but there still needs to be some manifold heat, even at full coolant temperature. If all you're doing is racing, and the carb is jetted rich enough that uniform mixture distribution between cylinders is a moot point- - - -then disable the heat riser. Street engines need at least some manifold heat all the time. Like I've claimed quite often- - - -doing race engine stuff on a street machine is going to be frustrating at best, and downright dumb at worst! Put a wireless BBQ grill thermometer sensor under the hood sometime to see what the whole engine compartment temp is- - - -you'll get a real education.
Jerry
