C3 Vette Registry - The Best Resource on the Net for C3 Vettes! C3 Vette
Forums -> C3 Engines
Not Logged In! Login or Register!  Users Online: 18 / Help 
Features  Find C3 Parts on ebay in only 2 or 3 clicks!  | Add YOUR C3 to the Registry

Supporting Vendors
Volunteer Vette Products
Bair's Corvettes
Mid America Motorworks

C3 of the Month
None Current
Enter Yours Today!
Online C3 Show
C3s are Registered

Vanity Plates
Featured Links

Buy Now
Corvette by the Numbers
Corvette by the Numbers

Corvette Fifty Years (Hardcover)
Corvette Fifty Years (Hardcover)

Motor Trend - $5 for 12 issues.
Motor Trend
Only $5 for 12 issues.

How To Rebuild Corvette Rolling Chassis 1963-1982
How To Rebuild Corvette Rolling Chassis 1963-1982

| Hide Signatures and Profile Pics

 New Topic New Topic Post Reply Reply New Poll New Poll Search     Search Page [1]  
10/25/12 3:47pm - Original Message: 'spark plugs'
Former Member
- Send Private Message


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.
 Reply Reply  Quote Reply w/Quote
Support C3VR!
Suport our advertisers
10/25/12 4:53pm - Reply: 'Re: spark plugs'
Former Member
- Send Private Message

Frederick, MD - USA

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!

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

Click image for larger pic
 Reply Reply  Quote Reply w/Quote
10/25/12 9:52pm - Reply: 'Re: spark plugs'
rod7515 Lifetime Member
Lifetime Member
- Send Private Message

Red Lion, PA - USA

1974 White 350 Corvette, TH400 Automatic 1972 Tangerine /Go Mango Convertible 383 Stroker, 2004r Automatic

Joined: 10/27/2006
Posts: 1180
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,


 Reply Reply  Quote Reply w/Quote
10/26/12 7:57am - Reply: 'Re: spark plugs'
manchestershark Lifetime Member
Lifetime Member
- Send Private Message

Equinunk, PA - USA

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: 1943
One heat range up is not out of the question, providing the HEI is in good order.


Click on image for full view
 Reply Reply  Quote Reply w/Quote
 New Topic New Topic Post Reply Reply New Poll New Poll Search     Search Page [1]  
 Forums -> C3 Engines
(Moderator: Adam Wartell, Norsky, Adams' Apple)

Official C3 Vette Registry Community:
Home | Forums | Email | Who's Online | Clubs | Events | Member Stats

Other Official C3 Vette Registry Areas:
Members | Research | Shop | My Account | About C3VR

Corvette is a registered trademark of the General Motors Corporation(GM) & Chevrolet Motor Division. Vette Registries, LLC is responsible for all site content (except for member submitted content or where otherwise noted) and does not claim or imply that Chevrolet or GM is responsible for Official C3 Vette Registry content. Vette Registries, LLC is independent from GM and is not affiliated with, sponsored or supported by GM.  Copyright/trademark/sales mark infringements are not intended, or implied and are in fact used to support GM, Chevrolet and Corvette

Official C3 Vette Registry content is Copyright 2001-2018, Vette Registries, LLC. Content may not be reused without written consent. All Rights Reserved. NS

Corvette (Vette) Model Years on this site: 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 30