Mike is 100% correct. The fuel pump has a one way check valve. After the engine is shut off, the trapped fuel in the lines between the pump and carbs expands from the heat under the hood. If the pressure exceeds 6 psi, the needle/seat will not stay closed. I have seen this occur on several Tri-Powers.
Adding a return vent like the A/C cars have is not a simple task. Setting the float levels slightly lower than spec sometimes cures this issue, You may also be aware that the center carb (pre '66) has a smaller float than end carbs. The float bowl on the small center carbs is the same size as the end carbs. Try using a larger float in the center carb. This results in added resistance to fuel pressure overcoming the needle/seat. I've done this with success.
Quote:
Originally Posted by mike w
This is usually related to fuel pressure. Fuel will not flow backwards through your pump. Under hood heat will expand fuel in line and increase pressure.
Try putting a gauge on the line and watch pressure raise after engine is shut off ; it will.
These carbs can only handle 4-5 pounds of fuel pressure. Most new mechanical pumps push 6-8 #.
A good fuel regulator should solve this issue. Holley makes a good 1-4# regulator for less than $50.
Your throttleshaft may be worn, but replacing it will not solve your problem. Fuel should not be dripping onto the throttle blades after shut off.
|