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whats the right spark plug?

3K views 21 replies 10 participants last post by  Cutlass327 
#1 ·
I have a 1984 jeep cj7 with a 4.0l punched out to 4.6l and its carbureted, but the spark plugs don't burn enough fuel, so does anyone now the number of a spark plug that burns hotter? please respond!:wink2:
 
#3 ·
What do you mean, the spark plugs don't burn enough fuel? Spark plug heat range has nothing to do with the spark temperature, but rather the rate at which the plug body dissipates heat. It won't necessarily run better with hotter plugs, though use of too low a heat range may cause more deposits to build up and foul the plugs. Is it running rich (black exhaust smoke)? Sooty deposits on the plug kusually low ignition output)? Oil fouled plugs?
 
#4 ·
HI, you have other problems..if its not burning all the fuel.. punched to a 4.6 tells us nothing about the motor, like cam, carb, ignition ect.. need more information .. stock plugs should work fine ... if not you have other problems.. more information please. maybe fill out your profile ...
How did you get .6 L increase ? I .30 overboard my 460 cu. and only got .1 L increase.
good luck
tim
 
#10 ·
Answering your question: (Which might not solve the problem) RC14YC.

The number indicates the heat range of the spark plug For Champion the higher the number the hotter the heat range. Generally speaking, a colder heat range is used under high temperature conditions such as racing, while a hotter heat range is used under colder climate conditions. It is best to use the heat range specified by the manufacturer.

R= Resister
C= 14MM Thread, 3/4" Reach/ 5/8" Hex, Gasket Seat
12= Heat Range
Y= Projected Tip
C= Copper Core

There you go. Trivia you probably don't need, but now you're ready for Jeopardy!

Could be anything from a messed up carburetor to a blown head gasket. (Hope not)

Fill out your profile! Include your altitude if you know it. As mentioned, it could be jetted wrong, or your choke could be messed up or a leaky needle valve or...

Is your coil putting out enough voltage? How old are the plug wires? What ignition system are you running?
 
#14 · (Edited)
It's at least a 3.94 bore (likely 3.95 which is .075 over) with a 3.89 stroke to hit 4.7L so it's definitely bored and stroked, not that it's relevant to his spark plug question :)


Shawn

Edit: My bad. I was thinking 4.7L. 4.6L would be at least a 3.9 bore 3.89 stroke so .25 over. Likely .030 over but bored none-the-less.
 
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#18 ·
Doe's anyone know where I can find RC14LYC champion spark plugs? I looked almost everywhere and can't find any for my cj.
If there are any cross references to if any are out there.
Levi.
I suggest you check the jets in your carb before tossing plugs at it. The 12's should work just fine, they are on the hot end, I think you are over rich.
 
#20 ·
I may have missed it, but what is your gap setting on your plugs?
Look at your plugs, that can be very telling of your issues. Replacing plugs may not solve your issues.

Are your plugs sooty? Wet? Tan color, brown/black? Pitted or eroded?
Do you have the original Duraspark ignition module? Original coil?

Plugs may not be your issue. If all your fuel is not burning in combustion, it is either too much fuel, or poor spark that is late. Have you checked your timing? What is it set at?

Info info info.
 
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