so this is the config now:

{
  "Permission": "quicksmelt.use",
  "Use Permission": false,
  "Speed Multipliers": {
    "furnace": 1000.0,
    "furnace.large": 1000.0,
    "refinery_small_deployed": 1000.0,
    "campfire": 50.0,
    "skull_fire_pit": 50.0,
    "fireplace.deployed": 50.0,
    "bbq.deployed": 50.0
  },
  "Fuel Usage Speed Multipliers": {
    "furnace": 0.01,
    "furnace.large": 0.01,
    "refinery_small_deployed": 0.01,
    "campfire": 0.01,
    "skull_fire_pit": 0.01,
    "fireplace.deployed": 0.01,
    "bbq.deployed": 0.01
  },
  "Fuel Usage Multipliers": {
    "furnace": 1,
    "furnace.large": 1,
    "refinery_small_deployed": 1,
    "campfire": 1,
    "skull_fire_pit": 1,
    "fireplace.deployed": 1,
    "bbq.deployed": 1
  },
  "Output Multipliers": {
    "furnace": {
      "metal.fragments": 1.0,
      "sulfur": 1.0,
      "charcoal": 10.0,
      "metal.refined": 1.0
    },
    "furnace.large": {
      "metal.fragments": 1.0,
      "sulfur": 1.0,
      "charcoal": 10.0,
      "metal.refined": 1.0
    },
    "refinery_small_deployed": {
      "lowgradefuel": 1.0
    },
    "campfire": {
      "bearmeat.cooked": 1.0,
      "chicken.cooked": 1.0,
      "deermeat.cooked": 1.0,
      "fish.cooked": 1.0,
      "horsemeat.cooked": 1.0,
      "humanmeat.cooked": 1.0,
      "meat.pork.cooked": 1.0,
      "wolfmeat.cooked": 1.0
    },
    "skull_fire_pit": {
      "bearmeat.cooked": 1.0,
      "chicken.cooked": 1.0,
      "deermeat.cooked": 1.0,
      "fish.cooked": 1.0,
      "metal.refined": 1.0,
      "horsemeat.cooked": 1.0,
      "humanmeat.cooked": 1.0,
      "meat.pork.cooked": 1.0,
      "wolfmeat.cooked": 1.0
    },
    "fireplace.deployed": {
      "bearmeat.cooked": 1.0,
      "chicken.cooked": 1.0,
      "deermeat.cooked": 1.0,
      "fish.cooked": 1.0,
      "metal.fragments": 1.0,
      "horsemeat.cooked": 1.0,
      "humanmeat.cooked": 1.0,
      "meat.pork.cooked": 1.0,
      "wolfmeat.cooked": 1.0
    },
    "bbq.deployed": {
      "bearmeat.cooked": 1.0,
      "chicken.cooked": 1.0,
      "deermeat.cooked": 1.0,
      "fish.cooked": 1.0,
      "sulfur": 1.0,
      "horsemeat.cooked": 1.0,
      "humanmeat.cooked": 1.0,
      "meat.pork.cooked": 1.0,
      "wolfmeat.cooked": 1.0
    }
  },
  "Whitelist": {
    "furnace": [
      "metal.ore",
      "sulfur.ore",
      "hq.metal.ore",
      "can.tuna.empty",
      "can.beans.empty",
      "bearmeat",
      "chicken.raw",
      "deermeat.raw",
      "fish.raw",
      "horsemeat.raw",
      "humanmeat.raw",
      "meat.boar",
      "charcoal",
      "wolfmeat.raw",
      "crude.oil"
    ],
    "furnace.large": [
      "metal.ore",
      "sulfur.ore",
      "hq.metal.ore",
      "bearmeat",
      "chicken.raw",
      "deermeat.raw",
      "fish.raw",
      "horsemeat.raw",
      "humanmeat.raw",
      "meat.boar",
      "wolfmeat.raw",
      "can.tuna.empty",
      "can.beans.empty",
      "crude.oil"
    ],
    "small.oil.refinery": [
      "crude.oil"
    ],
    "campfire": [
      "bearmeat",
      "chicken.raw",
      "deermeat.raw",
      "fish.raw",
      "horsemeat.raw",
      "humanmeat.raw",
      "meat.boar",
      "wolfmeat.raw",
      "can.tuna.empty",
      "can.beans.empty"
    ],
    "skull_fire_pit": [
      "bearmeat",
      "chicken.raw",
      "deermeat.raw",
      "fish.raw",
      "hq.metal.ore",
      "horsemeat.raw",
      "humanmeat.raw",
      "meat.boar",
      "wolfmeat.raw",
      "can.tuna.empty",
      "can.beans.empty"
    ],
    "fireplace.deployed": [
      "bearmeat",
      "chicken.raw",
      "deermeat.raw",
      "fish.raw",
      "metal.ore",
      "horsemeat.raw",
      "humanmeat.raw",
      "meat.boar",
      "wolfmeat.raw",
      "can.tuna.empty",
      "can.beans.empty"
    ],
    "bbq.deployed": [
      "bearmeat",
      "chicken.raw",
      "deermeat.raw",
      "fish.raw",
      "horsemeat.raw",
      "sulfur.ore",
      "humanmeat.raw",
      "meat.boar",
      "wolfmeat.raw",
      "can.tuna.empty",
      "can.beans.empty"
    ]
  },
  "Blacklist": {
    "global": [
      "bearmeat.cooked",
      "chicken.cooked",
      "deermeat.cooked",
      "fish.cooked",
      "horsemeat.cooked",
      "humanmeat.cooked",
      "meat.pork.cooked",
      "wolfmeat.cooked"
    ]
  },
  "Smelting Frequencies (Smelt items every N smelting ticks)": {
    "global": 1
  },
  "Debug": false
}​

Very nice! I did make a bit of a change, just bc I wanted furances and large furnaces to burn wood a bit faster for charcoal. This is amazing though! I've messed with this config SOOO many times and never seem to get it right. It's so very confusing! 

 "Fuel Usage Speed Multipliers": {
    "furnace": 0.1,
    "furnace.large": 0.1,
    "refinery_small_deployed": 0.01,
    "campfire": 0.01,
    "skull_fire_pit": 0.1,
    "fireplace.deployed": 0.01,
    "bbq.deployed": 0.01
  },​

Hello there! I have tried to use this modded version of your json file:

{
  "Permission": "quicksmelt.use",
  "Use Permission": true,
  "Speed Multipliers": {
    "furnace": 100.0,
    "furnace.large": 100.0,
    "refinery_small_deployed": 100.0,
    "campfire": 50.0,
    "skull_fire_pit": 50.0,
    "fireplace.deployed": 50.0,
    "bbq.deployed": 50.0
  },
  "Fuel Usage Speed Multipliers": {
    "furnace": 0.01,
    "furnace.large": 0.01,
    "refinery_small_deployed": 0.01,
    "campfire": 0.01,
    "skull_fire_pit": 0.01,
    "fireplace.deployed": 0.01,
    "bbq.deployed": 0.01
  },
  "Fuel Usage Multipliers": {
    "furnace": 0.1,
    "furnace.large": 0.1,
    "refinery_small_deployed": 0.1,
    "campfire": 0.1,
    "skull_fire_pit": 0.1,
    "fireplace.deployed": 0.1,
    "bbq.deployed": 0.1
  },
  "Output Multipliers": {
    "furnace": {
      "metal.fragments": 5.0,
      "sulfur": 5.0,
      "charcoal": 1.0,
      "metal.refined": 5.0
    },
    "furnace.large": {
      "metal.fragments": 10.0,
      "sulfur": 10.0,
      "charcoal": 1.0,
      "metal.refined": 10.0
    },
    "refinery_small_deployed": {
      "lowgradefuel": 5.0
    },
    "campfire": {
      "bearmeat.cooked": 2.0,
      "chicken.cooked": 2.0,
      "deermeat.cooked": 2.0,
      "fish.cooked": 2.0,
      "horsemeat.cooked": 2.0,
      "humanmeat.cooked": 2.0,
      "meat.pork.cooked": 2.0,
      "wolfmeat.cooked": 2.0
    },
    "skull_fire_pit": {
      "bearmeat.cooked": 1.0,
      "chicken.cooked": 1.0,
      "deermeat.cooked": 1.0,
      "fish.cooked": 1.0,
      "metal.refined": 1.0,
      "horsemeat.cooked": 1.0,
      "humanmeat.cooked": 1.0,
      "meat.pork.cooked": 1.0,
      "wolfmeat.cooked": 1.0
    },
    "fireplace.deployed": {
      "bearmeat.cooked": 2.0,
      "chicken.cooked": 2.0,
      "deermeat.cooked": 2.0,
      "fish.cooked": 2.0,
      "metal.fragments": 2.0,
      "horsemeat.cooked": 2.0,
      "humanmeat.cooked": 2.0,
      "meat.pork.cooked": 2.0,
      "wolfmeat.cooked": 2.0
    },
    "bbq.deployed": {
      "bearmeat.cooked": 3.0,
      "chicken.cooked": 3.0,
      "deermeat.cooked": 3.0,
      "fish.cooked": 3.0,
      "sulfur": 3.0,
      "horsemeat.cooked": 3.0,
      "humanmeat.cooked": 3.0,
      "meat.pork.cooked": 3.0,
      "wolfmeat.cooked": 3.0
    }
  },
  "Whitelist": {
    "furnace": [
      "metal.ore",
      "sulfur.ore",
      "hq.metal.ore",
      "can.tuna.empty",
      "can.beans.empty",
      "bearmeat",
      "chicken.raw",
      "deermeat.raw",
      "fish.raw",
      "horsemeat.raw",
      "humanmeat.raw",
      "meat.boar",
      "charcoal",
      "wolfmeat.raw",
      "crude.oil"
    ],
    "furnace.large": [
      "metal.ore",
      "sulfur.ore",
      "hq.metal.ore",
      "bearmeat",
      "chicken.raw",
      "deermeat.raw",
      "fish.raw",
      "horsemeat.raw",
      "humanmeat.raw",
      "meat.boar",
      "wolfmeat.raw",
      "can.tuna.empty",
      "can.beans.empty",
      "crude.oil"
    ],
    "small.oil.refinery": [
      "crude.oil"
    ],
    "campfire": [
      "bearmeat",
      "chicken.raw",
      "deermeat.raw",
      "fish.raw",
      "horsemeat.raw",
      "humanmeat.raw",
      "meat.boar",
      "wolfmeat.raw",
      "can.tuna.empty",
      "can.beans.empty"
    ],
    "skull_fire_pit": [
      "bearmeat",
      "chicken.raw",
      "deermeat.raw",
      "fish.raw",
      "hq.metal.ore",
      "horsemeat.raw",
      "humanmeat.raw",
      "meat.boar",
      "wolfmeat.raw",
      "can.tuna.empty",
      "can.beans.empty"
    ],
    "fireplace.deployed": [
      "bearmeat",
      "chicken.raw",
      "deermeat.raw",
      "fish.raw",
      "metal.ore",
      "horsemeat.raw",
      "humanmeat.raw",
      "meat.boar",
      "wolfmeat.raw",
      "can.tuna.empty",
      "can.beans.empty"
    ],
    "bbq.deployed": [
      "bearmeat",
      "chicken.raw",
      "deermeat.raw",
      "fish.raw",
      "horsemeat.raw",
      "sulfur.ore",
      "humanmeat.raw",
      "meat.boar",
      "wolfmeat.raw",
      "can.tuna.empty",
      "can.beans.empty"
    ]
  },
  "Blacklist": {
    "global": [
      "bearmeat.cooked",
      "chicken.cooked",
      "deermeat.cooked",
      "fish.cooked",
      "horsemeat.cooked",
      "humanmeat.cooked",
      "meat.pork.cooked",
      "wolfmeat.cooked"
    ]
  },
  "Smelting Frequencies (Smelt items every N smelting ticks)": {
    "global": 1
  },
  "Debug": false
}​​

But every time I reload the plugin, it does not work and I have a 823 bytes QuickSmelt.jsonError file along the QuickSmelt.json default file.

What am I doing wrong here???? I am really puzzled. My json file is validated.

The plugin is broken at the moment, wait for a fix

I got it working. It's weird, tho: it seems that it does not accept the "0.01" values. I had to set them to "1" and I don't understand why. Do you have an explanation? Does those values work for you instead?

I just read your answer! Ok, it seems I circumvented it somewhat. I will wait for the fix. Thanks for the explanation! :-)

if it works for you im curious about your config, can you share it?

{
"Permission": "quicksmelt.use",
"Use Permission": false,
"Speed Multipliers": {
"furnace": 100000.0,
"furnace.large": 100000.0,
"refinery_small_deployed": 100000.0,
"campfire": 50.0,
"skull_fire_pit": 50.0,
"fireplace.deployed": 50.0,
"bbq.deployed": 50.0
},
"Fuel Usage Speed Multipliers": {
"furnace": 0.01,
"furnace.large": 0.01,
"refinery_small_deployed": 0.01,
"campfire": 0.01,
"skull_fire_pit": 0.01,
"fireplace.deployed": 0.01,
"bbq.deployed": 0.01
},
"Fuel Usage Multipliers": {
"furnace": 1,
"furnace.large": 1,
"refinery_small_deployed": 1,
"campfire": 1,
"skull_fire_pit": 1,
"fireplace.deployed": 1,
"bbq.deployed": 1
},
"Output Multipliers": {
"furnace": {
"metal.fragments": 1.0,
"sulfur": 1.0,
"charcoal": 10.0,
"metal.refined": 1.0
},
"furnace.large": {
"metal.fragments": 1.0,
"sulfur": 1.0,
"charcoal": 10.0,
"metal.refined": 1.0
},
"refinery_small_deployed": {
"lowgradefuel": 1.0
},
"campfire": {
"bearmeat.cooked": 1.0,
"chicken.cooked": 1.0,
"deermeat.cooked": 1.0,
"fish.cooked": 1.0,
"horsemeat.cooked": 1.0,
"humanmeat.cooked": 1.0,
"meat.pork.cooked": 1.0,
"wolfmeat.cooked": 1.0
},
"skull_fire_pit": {
"bearmeat.cooked": 1.0,
"chicken.cooked": 1.0,
"deermeat.cooked": 1.0,
"fish.cooked": 1.0,
"metal.refined": 1.0,
"horsemeat.cooked": 1.0,
"humanmeat.cooked": 1.0,
"meat.pork.cooked": 1.0,
"wolfmeat.cooked": 1.0
},
"fireplace.deployed": {
"bearmeat.cooked": 1.0,
"chicken.cooked": 1.0,
"deermeat.cooked": 1.0,
"fish.cooked": 1.0,
"metal.fragments": 1.0,
"horsemeat.cooked": 1.0,
"humanmeat.cooked": 1.0,
"meat.pork.cooked": 1.0,
"wolfmeat.cooked": 1.0
},
"bbq.deployed": {
"bearmeat.cooked": 1.0,
"chicken.cooked": 1.0,
"deermeat.cooked": 1.0,
"fish.cooked": 1.0,
"sulfur": 1.0,
"horsemeat.cooked": 1.0,
"humanmeat.cooked": 1.0,
"meat.pork.cooked": 1.0,
"wolfmeat.cooked": 1.0
}
},
"Whitelist": {
"furnace": [
"metal.ore",
"sulfur.ore",
"hq.metal.ore",
"can.tuna.empty",
"can.beans.empty",
"bearmeat",
"chicken.raw",
"deermeat.raw",
"fish.raw",
"horsemeat.raw",
"humanmeat.raw",
"meat.boar",
"charcoal",
"wolfmeat.raw",
"crude.oil"
],
"furnace.large": [
"metal.ore",
"sulfur.ore",
"hq.metal.ore",
"bearmeat",
"chicken.raw",
"deermeat.raw",
"fish.raw",
"horsemeat.raw",
"humanmeat.raw",
"meat.boar",
"wolfmeat.raw",
"can.tuna.empty",
"can.beans.empty",
"crude.oil"
],
"small.oil.refinery": [
"crude.oil"
],
"campfire": [
"bearmeat",
"chicken.raw",
"deermeat.raw",
"fish.raw",
"horsemeat.raw",
"humanmeat.raw",
"meat.boar",
"wolfmeat.raw",
"can.tuna.empty",
"can.beans.empty"
],
"skull_fire_pit": [
"bearmeat",
"chicken.raw",
"deermeat.raw",
"fish.raw",
"hq.metal.ore",
"horsemeat.raw",
"humanmeat.raw",
"meat.boar",
"wolfmeat.raw",
"can.tuna.empty",
"can.beans.empty"
],
"fireplace.deployed": [
"bearmeat",
"chicken.raw",
"deermeat.raw",
"fish.raw",
"metal.ore",
"horsemeat.raw",
"humanmeat.raw",
"meat.boar",
"wolfmeat.raw",
"can.tuna.empty",
"can.beans.empty"
],
"bbq.deployed": [
"bearmeat",
"chicken.raw",
"deermeat.raw",
"fish.raw",
"horsemeat.raw",
"sulfur.ore",
"humanmeat.raw",
"meat.boar",
"wolfmeat.raw",
"can.tuna.empty",
"can.beans.empty"
]
},
"Blacklist": {
"global": [
"bearmeat.cooked",
"chicken.cooked",
"deermeat.cooked",
"fish.cooked",
"horsemeat.cooked",
"humanmeat.cooked",
"meat.pork.cooked",
"wolfmeat.cooked"
]
},
"Smelting Frequencies (Smelt items every N smelting ticks)": {
"global": 1
},
"Debug": false
}

Yes of course but if you read my previous message, I explained how I circumvented the probem. It seems that the *.json file do not accept values like 0.1 or 0.01 or, generally speaking, values below 1.0. Hence I just replaced them with 1.0

Here is my QuickSmelt.json:

{
  "Permission": "quicksmelt.use",
  "Use Permission": false,
  "Speed Multipliers": {
    "furnace": 100.0,
    "furnace.large": 100.0,
    "refinery_small_deployed": 100.0,
    "campfire": 50.0,
    "skull_fire_pit": 50.0,
    "fireplace.deployed": 50.0,
    "bbq.deployed": 50.0
  },
  "Fuel Usage Speed Multipliers": {
    "furnace": 1.0,
    "furnace.large": 1.0,
    "refinery_small_deployed": 1.0,
    "campfire": 1.0,
    "skull_fire_pit": 1.0,
    "fireplace.deployed": 1.0,
    "bbq.deployed": 1.0
  },
  "Fuel Usage Multipliers": {
    "furnace": 1.0,
    "furnace.large": 1.0,
    "refinery_small_deployed": 1.0,
    "campfire": 1.0,
    "skull_fire_pit": 1.0,
    "fireplace.deployed": 1.0,
    "bbq.deployed": 1.0
  },
  "Output Multipliers": {
    "furnace": {
      "metal.fragments": 5.0,
      "sulfur": 5.0,
      "charcoal": 1.0,
      "metal.refined": 5.0
    },
    "furnace.large": {
      "metal.fragments": 10.0,
      "sulfur": 10.0,
      "charcoal": 1.0,
      "metal.refined": 10.0
    },
    "refinery_small_deployed": {
      "lowgradefuel": 5.0
    },
    "campfire": {
      "bearmeat.cooked": 2.0,
      "chicken.cooked": 2.0,
      "deermeat.cooked": 2.0,
      "fish.cooked": 2.0,
      "horsemeat.cooked": 2.0,
      "humanmeat.cooked": 2.0,
      "meat.pork.cooked": 2.0,
      "wolfmeat.cooked": 2.0
    },
    "skull_fire_pit": {
      "bearmeat.cooked": 1.0,
      "chicken.cooked": 1.0,
      "deermeat.cooked": 1.0,
      "fish.cooked": 1.0,
      "metal.refined": 1.0,
      "horsemeat.cooked": 1.0,
      "humanmeat.cooked": 1.0,
      "meat.pork.cooked": 1.0,
      "wolfmeat.cooked": 1.0
    },
    "fireplace.deployed": {
      "bearmeat.cooked": 2.0,
      "chicken.cooked": 2.0,
      "deermeat.cooked": 2.0,
      "fish.cooked": 2.0,
      "metal.fragments": 2.0,
      "horsemeat.cooked": 2.0,
      "humanmeat.cooked": 2.0,
      "meat.pork.cooked": 2.0,
      "wolfmeat.cooked": 2.0
    },
    "bbq.deployed": {
      "bearmeat.cooked": 3.0,
      "chicken.cooked": 3.0,
      "deermeat.cooked": 3.0,
      "fish.cooked": 3.0,
      "sulfur": 3.0,
      "horsemeat.cooked": 3.0,
      "humanmeat.cooked": 3.0,
      "meat.pork.cooked": 3.0,
      "wolfmeat.cooked": 3.0
    }
  },
  "Whitelist": {
    "furnace": [
      "metal.ore",
      "sulfur.ore",
      "hq.metal.ore",
      "can.tuna.empty",
      "can.beans.empty",
      "bearmeat",
      "chicken.raw",
      "deermeat.raw",
      "fish.raw",
      "horsemeat.raw",
      "humanmeat.raw",
      "meat.boar",
      "charcoal",
      "wolfmeat.raw",
      "crude.oil"
    ],
    "furnace.large": [
      "metal.ore",
      "sulfur.ore",
      "hq.metal.ore",
      "bearmeat",
      "chicken.raw",
      "deermeat.raw",
      "fish.raw",
      "horsemeat.raw",
      "humanmeat.raw",
      "meat.boar",
      "wolfmeat.raw",
      "can.tuna.empty",
      "can.beans.empty",
      "crude.oil"
    ],
    "small.oil.refinery": [
      "crude.oil"
    ],
    "campfire": [
      "bearmeat",
      "chicken.raw",
      "deermeat.raw",
      "fish.raw",
      "horsemeat.raw",
      "humanmeat.raw",
      "meat.boar",
      "wolfmeat.raw",
      "can.tuna.empty",
      "can.beans.empty"
    ],
    "skull_fire_pit": [
      "bearmeat",
      "chicken.raw",
      "deermeat.raw",
      "fish.raw",
      "hq.metal.ore",
      "horsemeat.raw",
      "humanmeat.raw",
      "meat.boar",
      "wolfmeat.raw",
      "can.tuna.empty",
      "can.beans.empty"
    ],
    "fireplace.deployed": [
      "bearmeat",
      "chicken.raw",
      "deermeat.raw",
      "fish.raw",
      "metal.ore",
      "horsemeat.raw",
      "humanmeat.raw",
      "meat.boar",
      "wolfmeat.raw",
      "can.tuna.empty",
      "can.beans.empty"
    ],
    "bbq.deployed": [
      "bearmeat",
      "chicken.raw",
      "deermeat.raw",
      "fish.raw",
      "horsemeat.raw",
      "sulfur.ore",
      "humanmeat.raw",
      "meat.boar",
      "wolfmeat.raw",
      "can.tuna.empty",
      "can.beans.empty"
    ]
  },
  "Blacklist": {
    "global": [
      "bearmeat.cooked",
      "chicken.cooked",
      "deermeat.cooked",
      "fish.cooked",
      "horsemeat.cooked",
      "humanmeat.cooked",
      "meat.pork.cooked",
      "wolfmeat.cooked"
    ]
  },
  "Smelting Frequencies (Smelt items every N smelting ticks)": {
    "global": 1
  },
  "Debug": false
}​​

As you can see, there's nothing changed but the Fuel Usage modifiers (and some little tweaks here and there). This works 100% on my server. No errors, no compatibility issues (I also use k1lly0u's Night Lanter). Perfect.

Of course it would be rad if I could tweak the fuel usage a little bit down like 0.5 or something like that but I will wait. I am quite satisfied like that, so far.

"Fuel Usage Speed Multipliers": {
"furnace": 0.01,
"furnace.large": 0.01,
"refinery_small_deployed": 0.01,
"campfire": 0.01,
"skull_fire_pit": 0.01,
"fireplace.deployed": 0.01,
"bbq.deployed": 0.01

Does these values work for you???? Uhm....
Would you be my "guinea pig"? :-)))))

Would you try these values for me?

"Fuel Usage Multipliers": {
"furnace": 0.1,
"furnace.large": 0.1,
"refinery_small_deployed": 0.1,
"campfire": 0.1,
"skull_fire_pit": 0.1,
"fireplace.deployed": 0.1,
"bbq.deployed": 0.1

Because if the FUEL USAGE SPEED MULTIPLIERS don't give any errors to you, then whe have spotted what gives the errors.... The FUEL USAGE MULTIPLIERS! :-D

Me, on the other hand, will test your FUEL USAGE SPEED MULTIPLIERS values to check if they will crash the plugin.

I just tested your config and it only seems to make things even more slow!

Still it only adds like 3 metal fragments every X seconds. Not Quick at all. Feels like it's running on vanilla.

Any idea how to make it go faster? No matter if I use 100.0 or 1000000.0 it will go slow

NICE!!!! Your FUEL USAGE SPEED MULTIPLIER work like a charm so I guess that the problem is in the FUEL USAGE MULTIPLIER that gives an error.....

NICE NICE NICE! :-D

That's odd because I have just tested it and it's all but slow! On my server is crazy fast, the fuel (wood) consume really slow....
I cannot help you here, I am sorry.

Why don't you try to login on my server and test it there? 136.243.150.28:28016 I am online right now, I can help you out

Fuel usage speed multiplier only makes it burn wood faster and create more charcoal. But the actual smelting of the ore turning it into metal frags still goes super slow.

As I said, I totally don't know what's going on there. I am running smelting test and I am having 2k sulfur, hq metals, metal frags in less than 30 seconds. The only thing I can do is to invite you on my server and see it for yourself how it works. You have the address, you have my *.json file.

Too bad I am not a programmer and I am not the writer of the plugin... I don't know how to help you more than this. :-(