Heat soak is what happens when your engine has run up to operating temperature ( hot ) and is then shut off. The cooling effects of the circulating coolant, air flow and fuel flow all stop, and the heat from the engines combustion looks to escape through radiation. This takes time, and the engine's external parts heat up as the heat is transferred outward. Aluminum is a great heat conductor ( as in an aftermarket intake manifold and your carb body ) and therefore heat is conducted up into the body of the carb. The Q jet has a small centrally located fuel bowl, all nicely insulated and surrounded by radiant heat. As the heat increases, the fuel in the bowl boils away. When you come to re-start, you have to crank the mechanical pump over ( if you don't have an aftermarket electric pump ) to get fuel back into the bowl and re-start.
Resin block insulators are good, as they have a higher insulation effect then just a gasket. They will also raise the carb by a corresponding amount, so check you will have enough hood clearance. A large single central hole will also act like fitting a tunnel ram ( ie more flow at high rpm ( 4,500 upwards ) and boggy at low "driving rpm ( 1,500 - 3000). An insulator with the 4 holes would help, however make sure they fit your secondaries ( ie spreadbore to match the carb, not squarebore ). You may need to re-jet also.
The fuel supply / return is also important. As mentioned check your fuel pressure, fitting an inline gauge next to the carb will help. Also consider both an electric pump ( eliminates cranking on re-start ), and a return valve that will manage and prevent any vapour lock when it is hot and left standing.
Experimentation is your friend, as everyone's set up and driving needs are different.
Please post any changes you make, and the resulting effect. Will be interesting to know.
I am planning to experiment with both the new Edelbrock AVS II, and a re-built thermoquad for both around town driveability and moderate performance.
Cheers - A.
