Spark plug gap

[Anonymous]

Without going into the engine details, I have a 200 six I built, cam etc., I have the MSD 6A, blaster coil, had the dura spark built. I am using Autolite AP 46 plugs. My question is, what gap should I be using, I have heard everything from .50 to .65. They are set a .55 now and seem to be a little cold. Any suggestions?

Thanks in advance for any information.

 

[pro94]

thats a large gap. i would close it up alot. to 40-45 and try that. it takes a hot ignition to run that big of gap. dont get me wrong msd makes the best ignition componets in my opinion. but i dont think a 6a will run a 55 gap.

 

[JackFish]

Running a .050 gap on my fairmont, stock.

 

[cfmustang]

Wow, Pro94.

That is a nice looking car, but you need to shrink that avitar a bit!

 

[wsa111]

Jud, .045-.050 gap should be fine.

The AP-46 plug is a hot plug in the heat range.

I think you need to lean your idle mixture or even your cruising mixture?

I am very lucky to have an Innovate LM-1 air fuel ratio tester to check air fuel ratio's.

With the proper carburetor settings this spark plug should burn very close to an ivory color on the insulator to even a white color.

If you are using a vacuum guage to set your idle mixture you are adjusting your mixture way too rich.

Throw your vacuum guage away when you set your idle mixture.

The correct way to get the proper idle air fuel ratio is a slight lean drop method. A drop of even 15-50 rpm drop when setting your idle air fuel ratio will put you above 13-0 air fuel ratio for correct performance & proper idle air fuel ratio.

If you want the best fuel miliage use this lean drop method. William

 

[wsa111]

Readers, I have always had the use of an air fuel ratio tester.

I ran a tune up shop in the 70's

Then I used a marquette analizer which had an air fuel tester, now I have the innovate LM-1 air fuel tester.

This is a very hard question to answer, because of different sensitivity of the idle mixture screws on different carburetors.

As a starter set the desired idle 15-50 rpms above your desired setting then turn in the idle mixture screw to cause a lean drop in idle speed to a speed where you still have a decent idle quality.

Without the proper test equipment this will put you in the 13-1 & above range to achieve close to the proper air fuel ratio.

I would bet most of the readers have their idle air fuel ratio's in the 12-1 area, way to rich.

The idle mixture continues throughout the transfer range of throttle opening till the main jets take over above 2500-3000 rpm's cruising, that is why the idle mixture is very critical.

On the newer cars with a computer this adjustment is controlled electronically to over 14-1 & above to achieve proper emissions & fuel miliage which will follow with the leaner fuel mixtures.

With a carburetor you will not match a computer controlled vehicle, but you will come close on fuel miliage & power output. William

 

[xt falcon]

i had my carb tuned by feel just drive and adjust. when i hooked the wide band up it showed mid13:1 so i was not to bad now its at 15:1 but have not tuned the rest of the circutes yet.

my gaps are at between 2 and 1.8mm and dont seem to have any probs. i have msd cdi-6.