Too often my 454 is dieseling when I turn of the ignition. There is no carbon to speak of on the plugs, and I looked at the pistons with a borescope, there's little carbon in there (from what I can see). At this time, it idles fairly lean. Could that lean idle be super heating the plugs and causing this? I'd have to take notice again, but I don't think it will do it if I just come to a stop and turn it off right away. Aluminum heads. Compression is I think in the low 9's. Running 87 octane with no pinging. My old cure in other cars used to be to leave it in gear (automatic) when turning off the engine, but after a pretty hot ride yesterday it still did it while in drive. It's bad enough at home, but in public it's embarrassing!
55 Tony
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Yes, since dieseling can often be a combination of low octane gas, plus hot spark plugs, timing that's too advanced when running can result in even hotter spark plug electrodes. So the hotter the spark plug is more apt it to diesel after turning off the key.
A cooler plug, higher octane gas, and backing off the timing can all help avoid detonation, and dieseling after the key is turned off. Since the idle setting adjusts throttle plate position, it's going to have the same gas/air mixture with the key off or on. So if it idles with the key on, it can also diesel with the key off. But your engine idle speed doesn't sound too high at 750 rpm's, so not likely it's too high an idle speed.
A cooler plug, higher octane gas, and backing off the timing can all help avoid detonation, and dieseling after the key is turned off. Since the idle setting adjusts throttle plate position, it's going to have the same gas/air mixture with the key off or on. So if it idles with the key on, it can also diesel with the key off. But your engine idle speed doesn't sound too high at 750 rpm's, so not likely it's too high an idle speed.
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A cooler plug is a cooler rated plug, with less electrode exposed below the threads. So it runs cooler simply based on the recessed electrodes. It will run cooler regardless of timing, etc. than an extended electrode hotter plug.
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I had a car with an electric fan wired into the car via a simple on/off toggle switch. If I turned the key off with the fan switch on, the engine kept running! If I got out and disconnected the main battery cutoff switch, the engine still ran!
But if I switched the fan switch off first, the engine stopped as soon as I shut the key off. I installed a relay for the fan, and no more issues.
But if I switched the fan switch off first, the engine stopped as soon as I shut the key off. I installed a relay for the fan, and no more issues.
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Yes. Sorry, just forget the TS part. Should be an R44 for resistor plug, and #4 heat range.
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Holley specs say to size the power valve at 1/2 or less than the vacuum at idle. So what it does at higher rpm's isn't considered when sizing them. I've often found the idle vacuum isn't all that steady on most engines, so I look at the range it varies within, and go halfway from the middle. On my car it idles between 10"-12", so 11" is what I chose as my reference of what I'd go halfway from. And if I fudge it's towards a lower number, so instead of a 5.5 I'd drop to a 5 if I had them.
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Since you've already posted the Holley specs for power valve sizing, I wont need to go over them again. I simply set them the same way. I have a vacuum gauge permanently mounted in the dash of all my cars. Something I've done for decades on every build I've done as engine vacuum is such an important part of tuning pre computerized carbureted engines.
Once I've selected a power valve size based on the Holley way, I install them. Then I drive the cars to see how they feel, and smell. I check plugs visually to see if they have the color I want, and then based on the plug readings I select a larger or smaller jet size.
This has always worked fine for my tuning, and I've never considered spending the money for an air/fuel ratio gauge. I'd need one permanently plumbed in, as just sniffing the exhaust at idle wouldn't tell me what it's doing in all types of driving. So I am still doing it old school, and my engines seem to run fine.
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It is old, but it's also the same thing Holley has stated about tuning for decades. And it's the same recommendation others besides Holley, who built Holley style carbs, like Demon, and Quick Fuel also recommended.
Sometimes old info doesn't change.
I've never heard the 4 sizes smaller, and it seems odd to my thinking.
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Whatever happens during short acceleration is very tough to compensate for by changing power valves. The vacuum can vary greatly depending on the camshaft profile, and the load on the engine. So stabbing the throttle means very little towards choosing a power valve. Just like reading the vacuum after letting off the throttle and closing the butterflies in the carb means little. Either will result in huge swings of very low vacuum, and very high vacuum. So I don't choose a power valve based on either of these wide swings. I choose it as recommended, by idle vacuum.
For a race only drag car, one should be concerned about a lean mixture at full throttle, since those cars spend most of their life at wide open throttle, and constantly lean under that scenario could result in engine meltdown.
So drag racers rarely use a power valve at all. and prefer to block them off, and build and tune their carbs for wide open use.
For the street a carbureted engine often goes lean under acceleration, and wont usually harm the engine, unless it's extremely lean, and that way all the time.
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I think you know way more about Holley carbs than me. Guess I can't help you.
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