Piston Slap: A Stovebolt starving from a lack of fuel?


Larry writes:

I have a 1938 Chevy 1/2-ton pickup with an inline six-cylinder engine and manual transmission. The truck has an erratic problem. At times it starts, runs, and drives perfectly for months at a time. Then it begins to stall while driving and will not re-start until I prime the carburetor. Sometimes after priming, it will go dead again as soon as the prime is burned, and I have to re-prime. At these times, it will sit in the garage and run perfectly until I get it on the road and then the stalling returns, repeatedly. I am lucky to make it back home.

I have replaced the carburetor twice and also replaced the fuel pump, fuel lines, and fuel filter. I have replaced the spark plugs and plug wires. I am at my wit’s end. Can you help me?

Sajeev answers:

I have seen drivability issues like this before with classic cars, and the problem is usually exacerbated by the availability of ethanol blended fuels. But even if you are lucky enough to have pure gas in your area, modern fuels can still wreak havoc on your on-road performance. More to the point, gasoline has evolved over the years. Here are a few things you need to do to mitigate the problem, in no particular order:

  1. Install an in-line fuel pressure gauge in an easy-to-read location. This helps you monitor pressure when the motor starts to misbehave.
  2. Consider #1 but doing so with a gauge integrated into an adjustable fuel pressure regulator.
  3. Consider #2 but doing so while also installing a 12-volt electric fuel pump.
  4. Run heat insulation around your fuel lines.

Odds are there is no single fault with your truck’s fuel system, only that it wasn’t designed for the world we now live in. And even if these items aren’t enough to make your Stovebolt six-cylinder run like it did back in 1938, I reckon it will make a big difference. What say you, Hagerty Community?

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