Hello, I have a ‘59 Ford Skyliner with a rebuilt engine (7000 miles and 10 years ago) and the old carb was shot. Or so we thought...
Thanks for your detailed query, Craig. There are many reasons why carbureted vehicles run poorly in this age of ethanol-blended fuels. But assuming it still cranks easily (i.e. not from a bad starter or battery cables), let’s narrow it down to a pair of potential problems...
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I think the fundamental problem is that we have forgotten how to drive carbureted cars! When carbureted cars are parked after driving, the engines and carbs are hot, and the fuel in the carb evaporates. It may even boil. (And, yes, ethanol boils at a lower temperature.) The fumes—or liquid gas— winds up in the intake manifold and creates a too-rich mixture that will not burn.
When restarting a hot engine, hold the pedal down 1/4 to 1/2 way and crank. When the engine fires, continue to hold the throttle open a bit until the engine “clears its throat” and runs smoothly.
Pumping the gas pedal while cranking activates the accelerator pump, and makes the problem worse. For a severely flooded engine, it may be necessary to hold the pedal all the way to the floor while cranking in order to clear the fumes. Don’t over-rev the engine, but hold it at a fast idle until it clears.
I've run into the same problem on many carbureted vehicles these days, and a quick check will determine where the problem is. When the vehicle is up to temperature and has been running for the amount of time when the hard-start problem occurs, open the hood and remove the air filter lid. Manually operate the throttle and see if the accelerator pump shot is there. If it is, then there is enough fuel in the float bowl(s) to fire the engine. Replace the lid. Next, with some assistance, check for spark. I pull the coil wire and let it dangle near something metal, and have the assistant twist the key. The coil output should be visible even in daylight. If both of those items are present, fuel and spark, it should run. Is the ignition base timing correct, and does the distributor advance move freely? The ultimate solution that has cured 95 percent of the the old-car blues here in the Mojave desert is to fabricate a return-style fuel system. Hot engine compartments tend to vaporize the alcohol in the fuel line, and with the fuel deadheading at the needle and seat, it takes a while for the fuel pump to move enough vapor away before the cooler liquid fuel is introduced again. The downside to the return style system is that a non-vented fuel tank will over-pressure the carburetor when a hot engine is shut off, causing a flooding condition. Alleviate that with a vented fill cap, or as we have done, rig up a charcoal canister from a mid-70's GM truck, and vent the tank that way. Yes, it takes some effort, but your car will start better!