C.R. Miller Asks… Why Does My Corvette 350 Small-Block Miss and Stall Out When the Engine Gets Hot?
Q: I have a 1969 Corvette with a 300hp 350 engine. The engine was rebuilt several years ago with just enough bore to clean up the cylinders. It has the stock cam, stock heads with stainless steel valves, and a stock Rochester Quadrajet carburetor. It runs a 160-degree thermostat, a new heavy-duty water pump, and a nearly-new fan clutch.
When the engine temp nears 200 degrees Fahrenheit in heavy traffic, it starts missing and will shut down if I do not get off the road to let it cool down. It seems as if it’s experiencing vaporlock or the fuel is boiling out of the carburetor. In an attempt to isolate it from engine heat, the carburetor has three gaskets under it: fiber on the intake, a thick stainless steel plate, and another fiber gasket between the stainless and carburetor.
I went through the diagnosis steps in your recent engine vacuum troubleshooting article (“Your Vacuum Gauge is Your Friend,” Aug. ’19) and could not find an issue. I measured idle vacuum at just over 18 in-Hg and 22 in-Hg at about 1,500-2,000 rpm. I am
