What Causes Ignition to Fire early on Distributor Cap?

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66fyssh

66fyssh

Don't Stop Believin'
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What causes the spark on the leading edge of the distributor cap contacts? 1966 Barracuda, 273, Pertronix Igniter II, Flamethrower coil. I'm about 19* BTDC, 35* all in at 2500. close to 50* with vacuum advance connected.

The car runs great. Starts up quickly every time. Runs clean. Spark plugs look fine.

Should it be centered? The first picture is an old cap I replaced. The second pic is the new cap with about 800 miles on it.

Thanks for your input!!

Old Dist Cap.jpg


New Dist Cap.jpg
 
rotor phasing. Drill a hole in the cap so you can see the spark jump as it advances using a timing light.
Are you using a brass terminal cap? Aluminum does not cut it for longevity.
 
"Rotor phasing" is indeed what this is called. I'm not familiar with Pertronix, so I don't know how you would adjust / change that. In effect, the trigger point of the ignition, ---which is the Pertronix device--is not in sync with the rotor / cap.

If this were a factory points setup, and was doing this, it would have to be the advance plate is misaligned somehow with the rotor and cap.

Phasing DOES change some with vacuum advance. You might make certain you have the correct vacuum can Normally, the change from vacuum advance is "taken care of" within the width of the rotor / cap contacts.

The rotor and cap are not the problem unless they are just plain manufactured wrongly or you have the wrong cap....not the problem I would say.

Make certain the Pertronix parts you have are proper. Is the Pertronix kit different between BB and SB? I don't know, but the distriutors turn opposite between those engines
 
I can't add much to what has been said. It looks like the rotor tab is too high. If the magnet wheel is not properly seated on distributor cam, it will interfere with rotor seating down. Might be good to check index alignment.

The SB vs BB, and vacuum advance linkage or correct parts suggested by Del are likely too.
 
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The cap in the top picture has the insulating ribs on it, where the second done does. This helps prevent spark jumping...
 
Good catch Karl also is it me or is that terminal in the top left of the second pick turned around? and the insulation cracked? Do not have the beer goggles tonight.
 
halifaxhops said:
Good catch Karl also is it me or is that terminal in the top left of the second pick turned around? and the insulation cracked? Do not have the beer goggles tonight.
Click to expand...

Its just the lighting...and you without your beer googles!!:D

After researching phasing, it is definitely off. It very well could be a worn bushing, hops. More than likely the distributor is original and never rebuilt.

I have my next project!! At least I have an old cap to drill a hole into for troubleshooting.

Thanks again!
 
It is not pushed up and turned around? I need new glasses for sure from a 40. Take a look at the cap and make sure. Really looks that way to me and a small part of the back shoulder is missing and a crack towards the middle, really weird lighting any one else see it? Where is @ben drinking when you need him.
 
halifaxhops said:
It is not pushed up and turned around? I need new glasses for sure from a 40. Take a look at the cap and make sure. Really looks that way to me and a small part of the back shoulder is missing and a crack towards the middle, really weird lighting any one else see it? Where is @ben drinking when you need him.
Click to expand...

I'll pull it off and have a closer look. Yeah, where is @ben, LOL!!
 
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