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Old 06-07-2021, 11:13 AM   #1
Charlie ny
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Default spark plug recommendation

Guys,
I'm running Autolite 216's in my 286. Under sustained highway driving
I think the 216's are breaking down, the motor begins to run rough. The rough

running gives the effect similar to a wheel out of balance. All plugs are a reddish brown...the motor runs an L100 cam, lots of comp and a Stromberg
48 with # 50 jets. I've always preferred Autolites but I'm open to suggestions. The Autolite tech guy was no help.
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Old 06-07-2021, 11:36 AM   #2
flatjack9
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Default Re: spark plug recommendation

I use NGK B6L gapped at .025.
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Old 06-07-2021, 12:00 PM   #3
deuce lover
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Default Re: spark plug recommendation

X2 on the NGK
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Old 06-07-2021, 12:08 PM   #4
uncle max
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Default Re: spark plug recommendation

Another NGK fan here! B6-L for short reach and B5-ES for longer reach like Baron or Flatattack.
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Old 06-07-2021, 01:06 PM   #5
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Default Re: spark plug recommendation

After trying the H-10 and the 216 with not the best of luck I converted to the NGK and all is now good. The NGK B6L is the equivalent heat range to the H-10 and 216. The B-4-L can also be used if a slightly hotter plug is needed. With NGK the lower the number the hotter the plug for a gap with 12 volts go to .035
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Old 06-07-2021, 02:15 PM   #6
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Default Re: spark plug recommendation

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X3 on the NGK's
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Old 06-07-2021, 03:22 PM   #7
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Default Re: spark plug recommendation

I run the NGK B4L in my 286 CI Flathead. Seems to have eliminated my carbon buildup.
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Old 06-07-2021, 03:47 PM   #8
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Default Re: spark plug recommendation

Please help a Dummy here. I have a 1941 stock Flathead in a Coupe. What number NGK should I buy?
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Old 06-07-2021, 04:57 PM   #9
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Default Re: spark plug recommendation

Quote:
Originally Posted by Joe Immler View Post
Please help a Dummy here. I have a 1941 stock Flathead in a Coupe. What number NGK should I buy?

B6L unless it is a tired oil burner,then B4L.
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Old 06-07-2021, 05:27 PM   #10
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Default Re: spark plug recommendation

What does the reddish brown color on the insulator tell me ?....I'm thinking lean. ?
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Old 06-07-2021, 06:29 PM   #11
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Default Re: spark plug recommendation

Quote:
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What does the reddish brown color on the insulator tell me ?....I'm thinking lean. ?
Charlie ny
Usually in a lean condition the insulator will be white. Lean conditions cause lots more heat the high heat burns the material off the insulator showing its original color. The best color is a light brown the reddish coloring is odd possibly caused by the brand of gas your using.
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Old 06-07-2021, 08:41 PM   #12
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Default Re: spark plug recommendation

Thanks Ronnie......
NGK's on the way, very eager to file a report.
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Old 06-07-2021, 09:02 PM   #13
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Default Re: spark plug recommendation

Back in my snowmobiling days, reading plugs was very important. We wanted to go as fast as possible, and that meant "leanin' 'em down" as far as it was safe to go. Of course, if you went too far, you ended up with a hole in a piston, which wasn't good. In those days, we said that if you bought a Hershey Bar and broke a piece off, the color of the broken part was what you wanted your plugs to look like.

These days, gas isn't what it used to be, and Hershey Bars probably aren't either.
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Old 06-07-2021, 10:38 PM   #14
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Default Re: spark plug recommendation

It's close to Hershey chocolate.
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Old 06-08-2021, 07:49 AM   #15
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Default Re: spark plug recommendation

Quote:
Originally Posted by tubman View Post
Back in my snowmobiling days, reading plugs was very important. We wanted to go as fast as possible, and that meant "leanin' 'em down" as far as it was safe to go. Of course, if you went too far, you ended up with a hole in a piston, which wasn't good. In those days, we said that if you bought a Hershey Bar and broke a piece off, the color of the broken part was what you wanted your plugs to look like.

These days, gas isn't what it used to be, and Hershey Bars probably aren't either.
In as much as snowmobiles are 2 cycle and are oil burners, would you apply the same standards to a 4 cycle flathead that did not burn oil?
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Old 06-08-2021, 08:16 AM   #16
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Default Re: spark plug recommendation

Charley: Back in the day with a 239 with my foot in it, I ran H-9 plugs with good success. The stock jet for the Stromberg 48 is .048 and I am thinking your use of .050 is too rich, hence the color of your plugs. JMO.
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Old 06-08-2021, 09:25 AM   #17
Charlie ny
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Default Re: spark plug recommendation

Hi Bill,
The motor is a 286 cu in 8BA......L-100 cam.....max comp EAB heads. The rule
of thumb is no more than 2 #'s over stock so there's where I stopped. I will definately
check the color of the NGK's after another run on the freeway.
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Old 06-08-2021, 09:46 AM   #18
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Default Re: spark plug recommendation

NGK plus they are indexed, meaning the hexes are all
oreneted in the same position. G.M.
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Old 06-08-2021, 10:29 AM   #19
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Default Re: spark plug recommendation

Quote:
Originally Posted by 34PKUP View Post
In as much as snowmobiles are 2 cycle and are oil burners, would you apply the same standards to a 4 cycle flathead that did not burn oil?
I would. That color matched the pictures of the desired color in an old Motor manual I had. It's much easier to describe a Hershey bar to most people than to carry motor manual around with me every place I went.
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Old 06-08-2021, 10:52 AM   #20
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Default Re: spark plug recommendation

Coco brown is a good color on spark plugs but they can be a lighter shade toward gray and still be good. White or yellow would be too lean and of course black is too rich or too much oil loss into the cylinder.

The best way to check them is to motor down the road for a good bit and then shut down the engine and coast to a stop. This will give a good running color. If the engine is idling too long then the color can change on you.
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Old 06-08-2021, 10:59 AM   #21
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Default Re: spark plug recommendation

You'll find that with most of today's gas, that plugs don't "color like they used too". It is difficult to achieve a nice chocolate brown color . . . just never seems to happen for me. I tend to see colors that are a much lighter brownish/grey when the mixture is right.

As RoTo mentioned, you should do a test on the highway . . . is the only real way to do it. If you drive around, then come to stops and idle the engine . . . you'll find they almost always look too rich. So, you can't check the plugs after you go home - you'll not have accurate coloring . . .

Or, put some O2 sensor bungs in your exhaust and use a meter to tell you what is really happening.
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Old 06-08-2021, 05:55 PM   #22
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Default Re: spark plug recommendation

I had a similar issue at cruise speed, good advice on the plugs. In my case, the driveshaft was severely out of balance. Had a driveline shop balance it and all good.

JB
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Old 06-09-2021, 11:14 AM   #23
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Default Re: spark plug recommendation

anyone using autolite 386s? seem to work fine in my orig 37 flathead.
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Old 06-11-2021, 10:37 PM   #24
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Default Re: spark plug recommendation

Ronnie, I’m curious why you recommend a larger plug gap for 12 volts. Is the secondary voltage of a 12 volt system higher than a 6 volt system?
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