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reading spark plugs?
https://www.slantsix.org/forum/viewtopic.php?t=7982		 Page 1 of 1
Author:  guest [ Fri Jan 02, 2004 12:08 am ]
Post subject:  reading spark plugs?
It was time to tune up the old Dodge, I only have to do that every few years (low annual mileage). I seem to remember that plugs 3 and 4 should be a little darker (carbon, richer) than the rest. This time I was supprized to see 2 through 5 look great but 1 and 6 had some carbon buildup (dry, black). Now why might I see that? (or have I forgotten and they are the richer ones) One thought is that I often warm it up for 5 minutes before driving.

Its a stock '65 225 slant, rebuilt 50k ago. Holley 1920 carb, about 10 degrees initial advance, and I have disconnected the vacuum advance (it idles better without it).

Paul
Author:  Doctor Dodge [ Fri Jan 02, 2004 9:22 am ]
Post subject: 
Cylinders 1 & 6 can run rich because of "boundary" fuel washing down into those runners. This is caused by wet fuel that condenses on the outer walls of the manifold then flows right along the wall as liquid. It is hard to get this fuel to vaporize once it has "stuck" to the wall(s), especially if the engine never gets to proper operating temp.

The factory manifolds have a real short back wall so this is not a real big problem with them, the H. Pak manifold is bad about this to the point of washing-out plugs 1 & 6 if too much fuel is dumped into a cold manifold.

Best thing for you to do is to be sure the manifold heat riser is working and set the choke to come-off as fast as the cold engine will handle it.
Hot air intake also helps reduce the amount of fuel that condenses on the manifold walls. Getting you vacuum advance working again will also help keep the plugs burning cleaner.
(It sounds like your vacuum advance is pulling-in all the way at idle, that will make the engine idle rough, it can't handle 23+ degrees of initial timing, (10 degrees initial + all the vacuum advance)
Be sure you are plugging the vacuum advance into a ported vacuum source (not manifold vacuum) and see if the vacuum advance is the adjustable type, you nay need to add a little more spring tension to it, that will delay it's "tip-in")
DD
Author:  Paul [ Sat Jan 03, 2004 10:18 am ]
Post subject:  Re: reading spark plugs?
Doctor Dodge wrote:
>>Best thing for you to do is to be sure the manifold heat riser is working and set the choke to come-off as fast as the cold engine will handle it. <<

Got those taken care of. I don't put alot of miles on it so I do watch those, espcially the heat riser.

>>(It sounds like your vacuum advance is pulling-in all the way at idle, that will make the engine idle rough, it can't handle 23+ degrees of initial timing, (10 degrees initial + all the vacuum advance)

Be sure you are plugging the vacuum advance into a ported vacuum source (not manifold vacuum) and see if the vacuum advance is the adjustable type, you nay need to add a little more spring tension to it, that will delay it's "tip-in") <<

I'm not sure about adjusting the vacuum can, but its pulling in at idle. I only have one port to plug a vacuum line into. Its an old Holley 1920 carb.

I guess I forgot what holes get to much fuel. I should run it on the freeway more often too. Its life is so easy its hard :-)

Thanx,
Paul
Author:  Slant Cecil [ Sat Jan 03, 2004 3:28 pm ]
Post subject: 
Here's a link to reading plugs, but only after a full wide open throttle blast.
http://cochise.uia.net/pkelley2/sparkplugreading.html

Cecil
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