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10/25/12 2:47pm - Original Message: 'spark plugs'
sippy208
Standard Member
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Vette(s):
1981

Joined: 1/21/2006
Posts: 25
I need some help on selecting a plug for my 1981.  Its a 350 cu in. with a Holley Q Jet replacement carb, true dual exhaust ( no cat) MSD 6 AL ignition.  I currently have Accel 576 plugs, I recently put an alum. radiator in it.  The engine now runs alot cooler arround 170 degrees.  I pulled a plug and it was really black, i think its running too rich.  I was told to try a hotter plug.  Anyone out there that can give me some suggestions as to what plugs to use.
 
Thanks
Fred  
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10/25/12 3:53pm - Reply: 'Re: spark plugs'
Gunslinger
Former Member
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Frederick, MD - USA

Vette(s):
1969 convertible L71 427/435 4-speed black interior

Joined: 9/8/2003
Posts: 3398
If, in fact, it is running rich, changing spark plugs isn't going to fix it...adjusting the carburetor will.  

Using a CD ignition like the MSD usually recommends opening the spark plug gap up a bit.  Try opening it .005" and see how it runs.  If you feel that's OK...stick with it.  You can try opening the gap .010" and can see if there's any high rpm miss...if there is, close the gap back .005".  If there's no miss just stick with that.

As far as heat range, with an otherwise stock engine stick with the spark plug maker's recommended spark plug heat range.  You need to change the heat range to meet specific conditions or a modified engine.  

The brand of the spark plug shouldn't matter as long as it's the proper reach and heat range...and I know most have their favorite brand of spark plugs.  I wouldn't bother with exotic spark plugs...just what is equivalent to oe.  Buying exotic spark plugs for a car not using them as original equipment only serves to lighten your wallet and pad the wallets of the spark plug maker and their ad agency...but...you might get a nice decal to put on your car to tell everyone you use their super duper product!


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Poet...Mystic...Soldier of Fortune. As always...self-absorbed, adversarial, c o c k y and in general a malcontent.

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10/25/12 8:52pm - Reply: 'Re: spark plugs'
rod7515 Lifetime Member
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Red Lion, PA - USA

Vette(s):
1974 White 350 Corvette, TH400 Automatic 1972 Tangerine /Go Mango Convertible 383 Stroker, 2004r Automatic

Joined: 10/27/2006
Posts: 1172
I would agree with the "gunslingers" advice using the stock OE heat range. As for the black burning plugs I would ask how long have they been in and when you pulled them was it after a good run or after just starting it and warming it up. Does it load up when you first fire it up? My guess would be old plugs or something else causing it. Check your timing, make a carb adjustment if needed and see what happens. Keep us informed on what you find.
Best of luck,
Rodney

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10/26/12 6:57am - Reply: 'Re: spark plugs'
manchestershark Lifetime Member
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Equinunk, PA - USA

Vette(s):
1972 conv, 4-speed, 350, 200hp, numbers match, rally wheels, war bonnett yellow w/white top. good condition, nice driver.

Joined: 10/31/2007
Posts: 1901
One heat range up is not out of the question, providing the HEI is in good order.

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