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I have a 1954 Convertible with the 359 engine and the original aluminum head. I'm using Champion RJ8C spark plugs, which would seem to be the lineal descendants of the J8 listed in the shop manual. I use premium fuel. The pinging happens only when under load, never when revving in park or neutral. I can eliminate the pinging by retarding the distributor several degrees, but the idle is very unsteady, vacuum gauge fluctuates between 13-15 inches until the RPMs go over 600. I have disconnected and plugged the vacuum advance, that made no difference.

I'm wondering if a colder spark plug might help, but it looks like Champion doesn't make a colder plug. The only other plug they recommend is the RJ12YC; the 12 in the part number indicates that it is hotter than the RJ8C. If anyone has solved this problem, I'd appreciate knowing what the solution is. Thanks.

Does the pinging occur at highway speeds and climbing a hill? And if you back off the throttle a bit it will stop pinging?

Could you be running too lean?

Running lean due to carburetor issues or a vacuum leak could cause it. A low carburetor float level could cause lean out and pinging, as could a restricted fuel supply. A problem with the distributor vacuum or centrifugal advance mechanisms could cause it. A stuck manifold heat valve could contribute to it.

A problem with the water distributing tube, if present, could cause it.

Be sure the plug wires are in the correct firing order. The engine should idle and run smoothly even with the initial timing set a few degrees later than spec.

Vacuum leaks can occur at the intake manifold gaskets, carburetor gaskets, throttle shaft, vacuum booster pump, and anywhere in a vacuum windshield wiper system or any other vacuum device, including the vacuum advance or an automatic transmission vacuum modulator.

***Overheating or heavy carbon deposits can also cause pinging. In the case of carbon deposits, driving the car on the open road for a few dozen miles at 50 to 60 MPH will usually get rid of it. Avoid hard acceleration or driving with continuous pinging.

Stale gasoline can lay down heavy combustion chamber deposits in a hurry, and stale gasoline may have much lower octane than it did when fresh. Be sure your gasoline is fresh.

I haven't brought it up to highway speeds. It starts pinging when starting off slowly up gentle inclines. On steeper inclines I try to get a running start and feather the gas pedal. This stops the pinging for the most part, but not completely. This limits speed to 20 MPH or less. The pinging will stop if I let up on the gas pedal. Thank you for your questions.

Thanks, Big Kev for your question. I don't think it's running lean. The carb was professionally overhauled in October by a shop that's been around for 52 years and is very highly regarded. I have richened both screws on the carb, didn't see any difference so I set them back to 2 1/2 turns out.

This sounds like more that just a little pinging, sounds rather extreme.

Did it used to be okay and then something changed? If so can your correlate it to any work?

Is your vacuum advance the correct one and functioning? I think the ones for those years are not reproduced, so maybe your vacuum advance is not the correct model?

Has your distributor ever been serviced? Maybe the mechanical advance isn't working?

I wonder if there is a possibility that your timing is off? Maybe your pointer shows it's set at 6 degrees, but the pointer is off? That is maybe what shows as TDC is not TDC.

To me this sounds like bad timing. Maybe some plug wires mixed up? Maybe bad plug wires? Maybe the little screw connectors on the top of the plugs are loose?

The other thing that can mess up ignition is a bad coil. I had to replace a NAPA coil that was only a year old because it was doing crazy stuff after the oil leaked out. Generally bad coils get worse as they warm up.

And it could be a combination of a couple of things.

You'll find it, just gotta keep hunting!

Have you looked at the combustion on an exhaust gas analyzer?

Thanks, TxGoat for your suggestions. The vacuum gauge didn't detect any vacuum leakage. In checking things over, I found one of the four carb mounting nuts was a half-turn loose but tightening it didn't make a difference. Since I had no idea how old the vacuum advance was and it may have a tiny pinhole in the diaphragm, I bought a rebuilt one from Max (new ones are NLA) and that made no difference. The carburetor was run-tested by the rebuilder in October, so I doubt the problem is carb-related. I also don't think there's a fuel supply or a centrifugal advance problem as it revs up fine and doesn't ping in park, only under load does the condition appear. I always add stabilizer when refueling and the fuel that was in the tank over the winter passed the sniff test so I don't think it was stale. I filled the tank in May so most of the fuel is fresh. The heat riser valve works fine, moves smoothly through its travel. The weight drops as the engine warms up and comes back up when the engine cools.

The plug wires are in their proper order and they all Ohm out within specs, so it's not a wiring problem. As an FYI, there is no timing pointer on this engine so I time it by watching the vacuum gauge. A correctly-timed distributor will have the vacuum advance mechanism level and pointing straight ahead, so in the 9:00 position. I've experimented with the distributor at different positions, the pinging is eliminated at the 7:30-8:00 position. This, however, gives a low vacuum reading at idle and the gauge reads "late ignition timing." I drove it this way in a July 4th parade. I had to drive up a fairly steep hill to get there with three passengers aboard and it didn't ping at all. It went through the parade fine although I shifted into neutral and gave it a little gas to overcome the unstable idle when the parade came to standstills.

I'm toying with the idea of backing off the plug wires one terminal at the distributor cap which would give a 45 degree retard, then reset the distributor back to the 9:00 position to see what happens. Thanks for reading this diatribe.

The thing that jumps out at me is no timing pointer. I get timing by vacuum, but my next step would be to get, or make, a pointer so you can also use a timing light so you know where your timing is set for sure. I would be suspicious that you're timing may be more advanced than it should be.