hei plug gap
Thread Starter
Racer
Joined: Oct 2009
Posts: 280
Likes: 1
From: cleveland Ohio
hei plug gap
my 68 has a 1406 edelbrock carb with a edelbrock intake, its a 327-4 speed with a mallory hei distributer, runs good,but it doesnt always just start rite up,wondering if i should change my plug gap from 35 to 45 or 55 for better starting and or better performance. what do you guys think. thanks tom
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
You should set the plug gap according to the ignition module and coil that you are using. The stock GM HEI system requires .060" plug gap. You can set it lower, but then you just lose the benefit of the higher spark potential that the HEI system can provide. Set the gap as wide as the module and coil will allow.
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Race Director
Joined: Aug 2004
Posts: 10,628
Likes: 132
From: Duvall, WA
Why do you suspect your spark gap as being the cause of the car "not starting right up"? Does it do this after it's been sitting a couple of days? It could just be that the fuel in your Edelbrock carb is evaporating and you have to crank it until the fuel pump fills the bowl back up. Modern fuel evaporates pretty quickly.
Race Director
Joined: Jul 2001
Posts: 15,892
Likes: 42
You will notice NO positive change, maybe a possible misfire if the ignition system can't handle a .060 gap.
Thread Starter
Racer
Joined: Oct 2009
Posts: 280
Likes: 1
From: cleveland Ohio
my whole reason for this thread was because when i got the 68 in oct. 09 it can with the engine freshly rebuilt,only 300 miles on the engine,i would drive it every day for about a half hour,and if i would shut it off to get say , gas. it would either start right up, or become tempremental and have to crank and crank it,then you would have to pump the pedel abit, alittle bit,or it would be on the verge of flooding it,making it real hard to restart.since then ive changed the plugs,still runs real good,but still tempremental, espically at restart.thats why i was wondering if the plugs needed gaped to 60 with hei system. ill just have to have the carb dialed in and the timing checked,otherwise she flies real good. thanks again for all replies tom
Advanced
Joined: Sep 2005
Posts: 83
Likes: 0
From: Santa Barbara Calif
Sounds like a Vapor Lock to me. Turning the engine off when warmed up and time to add gas and restart is enough time for vapor lock to occur. Make sure gas lines are away from engine block and you may have to add heat shield gasket under carburator. I also added an electric fuel pump near the gas tank. End of my problems on hot restarts.
Advanced
Joined: Sep 2005
Posts: 83
Likes: 0
From: Santa Barbara Calif
Carb Gasket to insulate from heat .
Gasoline evaporates (boils) at a lower temperature than it use to. Its not as important with fuel injection. You need to find out which one fits your carb. They are usually a metal gasket between two regular gaskets
Edelbrock #9266 Carburetor Gasket- Heat Insulator, Square Bore.
E11-9266
These Edelbrock heat insulator gaskets are designed to help prevent fuel percolation in Performer series carburetors exposed to extreme underhood temperatures. They're available in both open and ported styles, and come complete with extended-length carburetor studs.
Instructor
Joined: Jan 2006
Posts: 228
Likes: 1
From: Warwick New York
Spark plug gap is variable depending on motor components and is usually determined by proformance and reading of the spark plugs themselves. Racers in the past would gap plugs different for each cylinder. Starting in 73 GM went to HEI and there gap started at 40 and progressed over the years to 60. a under gapped plug could fowl and cause poor starting. Get an old service manual that has a color spark plug chart and try to match it to the good ones.
