Is this really a hot start problem?

Question:

I really enjoy reading the Mechanic on Duty column in Auto Restorer.

As a newcomer to the hobby, I’ve found that your advice has been quite helpful in solving similar problems I’ve had with my first project.

I’m writing in hopes that you can help me with a “hot start” issue I have with my 1973 Dodge Dart. I’ve installed a 225 slant six ignition, and installed a new pickup in the distributor. The car runs extremely well with no hesitation or high speed drivability problems. It starts great in the morning and the choke seems to be working normally.

But if I drive the car 20 miles or so and stop, cut it off, and try to restart it within a 10or 15-minute time frame, the engine has to turn over several revolutions before it starts. After it starts, it takes a few seconds for it to “clear itself out,” then it runs beautifully.

I’m told this is a heat issue. I’ve tried all sorts of insulation around the model 1910 Holley carb with no results. The spec for the timing is correctly set at 0 degrees TDC, with the idle speed set at 750 rpm in neutral. I’ve even tried using two thicker gaskets under the carb to dissipate the heat.

I’ve also experimented with higher and lower heat range spark plugs. I’ve even thought about lowering or raising the float level in the carb. I feel the problem lies in the fuel system due to fuel “boiling” in the float bowl. Does anyone such as Holley, Edelbrock, Carter, etc., offer a better carburetor I can use to remedy this problem, or am I looking in the wrong direction?

Answer:

I’m not convinced that you actually do have a problem with starting your engine when it’s hot. You state that the engine has to “turn over several revolutions before it starts” but how many revolutions are we talking about here? Three or four is “several,” and in my opinion there’s nothing wrong with a decades-old carbureted engine taking three or four revolutions to fire up when it’s hot and then take a few seconds to smooth out.

If, however, there is a problem then it is most likely fuel related. A “better” carburetor is not the answer. Insulating the fuel system and reducing under hood temperature would, however, help.

Using two thicker gaskets under the carburetor may not help as much as you think. An insulator in addition to the gaskets will help keep the carburetor cooler. High quality heat insulation for the fuel lines and external filter, if your car is so equipped, is also highly recommended. You can buy this at many auto parts stores and speed shops or from many different Internet sources (such as Heatshield Products, heatshieldproducts.com).

And if you want to go the extradistance, install a thermostatically controlled, high-volume electric fan in front of the radiator and set it to go on at a low enough temperature so that it remains on for at least a few minutes after the engine is shut off when at full operating temperature.