![]() Read the paragraph "Vapor Lock Volatility". No question about it, this is what's causing the OP's hard start issue. Heat soak, allowing the fuel to boil, or simply evaporate, is technically "vapor lock". ![]() Hot rod fix, dual exhaust moved away from fuel line Pull over and let it cool down and hope you had enough battery to reprime the pump when it was cool.īest fix, install electric fuel pump to push the fuel, instead of sucking it. Pulling a hill on a hot day the exhaust heat would warm the supply line until the partial vacuum between the tank (rear) and pump (front, engine) would allow the fuel to change state to vapor. 1940's and 50's Chevy's were famous for this. Vapor lock is vaporizing the fuel in the supply line from the tank. You don't have to buy one part or spend more than 2 minutes on this test.īoiling fuel out of the carb is not vapor lock. If they shoot good and strong and the engine still fails a hot restart, then we know it's something else. If they're not spraying correctly under the typical failure situation, then we know your carb is evacuating fuel. ![]() If you don't know what I mean, post a pic of your carb with the flame arrestor removed and I'll circle the accelerator pump arm and the pump Jets. See if you get good, strong shots of fuel from your pump Jets, or if it looks piddly or you get nothing at all. It does have a thick black gasket at the bottomĮasy test: Give a push on your accelerator pump on the carb once the engine is in a state where it would usually fail to start. There are two spots on each side if the manifold where the paint is flaked off from the heat. You also don't have an engine bay baking with 200° heat after shutdown like a car. Your engine doesn't have bare exhaust manifolds glowing with exhaust heat. Unless you have some serious restriction in your fuel lines, I wouldn't worry about that or insulation. Your carb engine almost certainly does not have a fuel cooler, so I wouldn't worry about that. Phenolic carb spacer or the "thick" carb gasket (if Quadrajet) is the next thing to do. I've watched water boil off of the intake manifold where the crossover comes through. Easy way is to use one of the FelPro intake manifold gasket kits that includes stainless restrictors and block-offs for the crossover. If your intake manifold has an exhaust crossover, that is the first thing that needs to go. Vapor lock can still happen, but that would take a ridiculous amount of restriction in his lines. Hence my greater suspicion that he in fact has fuel boiling or vaporizing out of his carb. Vapor lock is pretty much unheard of on the carb systems. On shutdown, the raw water flow path becomes convection heated by the engine oil cooler (if applicable) power steering cooler, engine, or heat exchanger, and also the fuel pump. Once the brass/copper cooler takes on a good bit of corrosion layer in the raw water flow, the battle between the heater (pump) and the cooler (fuel cooler) becomes a losing battle for the cooler. The pump itself has a thermal bond to the fuel cooler body, but runs seriously hot, being a single stage high pressure pump. The module itself is also enclosed with no water or fuel jacketing. In the middle of all of this, there is no vapor separator tank (nobody does this either) and fuel is being constantly recirculated onto itself. ![]() The pump has to suck fuel all the way from the fuel tank into the engine mounted fuel water separator, and then across the engine to the fuel pump module mounted on the other side. ![]() The "cool fuel" vapor lock problem mostly came about from Mercruiser using a single stage high pressure fuel pump for fuel injection duties (nobody does this). True enough, but we have so many guys using ethanol and carb without this issue that I can't really say that's a given in this situation. ![]()
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