Piston Slap: Stalling Stude’ requires second opinion?


Jeff writes:

I have a ’63 Studebaker Avanti which will start up, run for five seconds, and then shut down. I have changed filter and use gas preservative. Car will continue to start up and shut down, many times. Fuel pump is working (has an electric as well as a mechanical pump). Any thoughts? My mechanic has replaced the condenser several times recently, not sure why; would this do that? Or is the float not opening up the needle valve? Thanks for any suggestions.

Sajeev answers:

Great question! By any chance do you have a fuel-pressure gauge on the fuel line, or one that you can connect to monitor the pressure as the motor stalls out? We need something like this to 100 percent rule-out a weak/failing fuel pump (or pumps). Or perhaps there is too much fuel pressure and the carburetor is flooding itself … but odds are that would be very noticeable.

Anyway, once the fuel pressure is confirmed to be within spec (usually 5 to 10 psi), we can consider an issue with ignition. Tell me what you think.

Jeff replies:

I am not a car mechanic, so don’t really have ability to do that. However, it seems to me that the chances of two fuel pumps failing at the same time would be like winning the Powerball. I can hear the electric one. I don’t think it is flooding out, no strong gas smell.

Sajeev concludes:

Perhaps my initial request to check for fuel pressure isn’t necessary, but that’s usually where I start. Voltage drop(s) can take both pumps out, but maybe the stalling Studebaker needs another opinion.

You can take apart the carb, give it a good clean, or a full rebuild. Or, don’t touch the carb yet and check for vacuum leaks (via smoke testing) or check the resistance of parts of the ignition system. Odds are it isn’t a vacuum leak, because it runs for a few seconds. The ignition could be an issue, especially if it’s been upgraded with non-standard parts that are either used (i.e., worn out when removed from the junkyard) or of poor aftermarket quality.

But, again, ruling out fuel pressure makes it easier to determine if whether you’re facing a fuel, spark or vacuum leak. And a drop in fuel pressure really feels like the first place to look.

What say you, Hagerty Community? Is fuel pressure the first thing you’d look for?

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    I would troubleshoot the electrical and ignition system by observation. Look under that distributor cap. Do the points look good. Is the vacuum line to the distributor soundly connected.
    Next consider that your carb float bowl is empty because the inlet valve or float got hung up. 12v systems that vintage have a capacitor on the way to the distributor.
    Switch it out with your spare (you have one right?) Fuel line blocked with corrosion? You use non ethanol right? Ethanol promotes rust in seldom used cars. Not always but a neutral safety switch can be a bad connection. Bypass it to test. I think the fuel delivery is your issue. There is my three cents worth from driving antique cars for 50 years including three Studebakers.

    Connect with the Avanti community via the Studebaker Driver’s Club. Could be some quirk their membership would advise you on in moments…

    Some Avanti have fancy supercharger setups iirc? Who know what other weirdness is there…

    Studebaker has been gone since mid 60s and wasn’t exactly a huge seller. Brand specialty knowledge isn’t going to be a part of many modern mechanics work history so things they may not think of might be the “this is how you fix that”.

    If you aren’t comfy with installing a fuel pressure gauge (nor have the tools to do it), there is another way to check for fuel delivery issues. Have you tried to bypass the fuel system with the old “dribble some fuel into the carb” method? You disconnect and plug off the fuel line (if it’s a rubber hose, you can maybe just double it back on itself and clamp it). Then, remove the air filter so you can see down into the venturis (throat of the carb). Have someone dribble a trickle of gas into that throat as you start the car. It takes a little coordination to drip enough but not too much. If the car continues to run for longer than those few seconds, your problem is fuel-related. If it still stalls out, it’s more likely electrical – at least you will have maybe ruled out one problem option.
    I’m voting for an in-carb issue, though. Sticking floats and needle valves have been, in my experience, far more responsible for the type of behavior you describe. I’m betting that Sajeev’s advice of a carb service or rebuild will prove to be the solution.

    If this was a Chrysler of this vintage, I would say that it has a failing ballast resistor. It has all the symptoms.
    I’m not sure if Studebaker used a similar arrangement.

    I was going to go along the ignition circuit line as well – starts and runs on resistor bypass but stalls shortly thereafter…

    It’s been a while but isn’t the symptom of a bad ballast resister that the engine only runs when the starter is engaged?

    As the starter spins down, it will backfeed electricity to the distributor for a few seconds. At least on an old Chrysler.

    If this happened suddenly – like it ran fine day or so before and no changes had been made – you could check for fuel starvation by having a helper carefully spray gas into carb to see if it keeps it running and check for spark with a spark tester (sparks when it runs for the 5 seconds and then disappears?). That could at least narrow it down to fuel or spark.
    Hope you have good luck and it is something simple to repair.

    I have no professional background, but my degree from YouTube points me more toward ignition rather than fuel. But the advice to check with the owners group is a good one. I bet someone there has had a similar issue.

    Based on the symptoms provided, I would check the ignition system as others have suggested. Check the temperature of the ignition coil at the point when the engine shuts down. If it’s very hot to the touch, it’s probably on the way out.

    Check the adjustments for the choke unloaded, it may be opening choke too wide after initial startup. The usual adjustment is about 1/8”use a 1/8 drill bit between carb body and choke plate.

    Several already mentioned, a failed ballast resistor will do this. this is pretty common on Jet boat motors with Mallory ignition systems, point style. To drip feed the carburetor is a good idea to diagnose fuel delivery on start up. Use an old-fashioned pump Oil can to pump the gas in one squirt at a time. Small engine squirt slowly big rat motor squirt fast!

    My Camaro would run for about 10 minutes then inexplicably stall and not start. I couldn’t figure it out then I noticed a small drop of fuel on the garage floor and lo and behold the fuel pump was taking suction but drawing a little air until finally the float bowl was empty and the car would stop. It is also possible that the fuel suction pipe inside the tank has a small leak and can’t bring the level all the way down.
    To determine if it is fuel or ignition run a hose from a gas can to the fuel pump. Also check the original fuel pump diaphragm for leakage, and smell the lube oil particularly if the level goes up. It’s possible the electric fuel pump is blowing gasoline in the sump.
    If it is ignition make certain all connected are clean and tight, and that the wires going from the coil are well insulated at the distributor.

    Here’s a real easy way to tell if the carb is starved. After it stalls, look down the throat of the carb and pump the throttle. If it squirts gas out the accelerator nozzle, then I don’t think starvation is the issue.

    Check the condition of rubber hoses between your fuel tank and the carburetor.
    These hoses deteriorate by age and new fuels with ethanol with a serious risk of pumping false air in the fuel lines. I lived this problem with a 1961 Impala. New hoses and problem solved !
    Herman De Ploey-Antwerp-Belgium

    It’s not the ignition system. As Kevin stated it’s probably in the pump jet circuit. It could be clogged, the seal can be bad, or could have a gummed up, or missing/ misplaced check ball. It’s not likely to be the float because that usually happens when it’sl warm causing a vapor lock in the carburetor.

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