I'M STUMPED ON THIS ONE on 340

[dpcd67]

340, ten to one CR.  Comp 268 cam. ED 2176 intake. ED 1406 carb. Champion N-11-Y plugs.
Runs great, but some richness/black smoke out the left exhaust.  I pulled the plugs and all are nice tan color, EXCEPT the #1 and #7 which are sooty black. No oil.
How can this be?
Help, please.

[Chryco Psycho]

Seems like the left side of the carb is tuned rich the shortest runners from the plenum are 1 & 7 so fuel would run downhill into these cylinders I have always had trouble with the 1406 carbs they seem to be the lowest quality even from  edelbrick , anything is better !
 Have you disassembled the carb checked float levels etc they are never right from the factory IIrc it it 7/16 - 3/8" float level  , make sure the jets are tight etc .

[dpcd67]

Thanks; I have not checked inside the carb but I will check float levels. I guess I believed the Edelbrock advertising about being able to "bolt on and run".  It did do that......

I forgot to add that I put on a fuel pressure regulator and set it at 5.5 psi, but it did not help the smoke thing.

[cudabob496]

bad valve guides?
Leaking intake manifold gasket, which can suck
oil from crankcase into intake valve, then cylinder.
been there.

[dpcd67]

It ain't oil that is burning; it is not burning the gas on two cylinders; I now suspect plugs, or wires.  Checking those today.

[jimynick]

If you could find one of the old oscilloscopes, you could check the ignition function on every cylinder- while it's running. Failing that, I'd swap another cylinders plug wire and stick a new plug in the dark hole and see if it improves. Check the gap as well and have a look inside the cap for any nastiness there as well. Just my 

[Chryco Psycho]

A thermal reader will measure temp from each cylinder but like will only tell you what you know that the 2 cyliders with blackened plugs are running colder

[cudabob496]

If you could find one of the old oscilloscopes, you could check the ignition function on every cylinder- while it's running. Failing that, I'd swap another cylinders plug wire and stick a new plug in the dark hole and see if it improves. Check the gap as well and have a look inside the cap for any nastiness there as well. Just my 

or check temps of exhaust header pipes

[brads70]

A thermal reader will measure temp from each cylinder but like will only tell you what you know that the 2 cyliders with blackened plugs are running colder

What about running a different heat range plug in those two cylinders?

[dpcd67]

I changed all the plugs to N12Ys; I was running 11s; just to make sure I didn't have any bad plugs. I changed the cap and rotor. I have not fired it up yet, but when I do, I will check the wires too, for bad wires.  I tried to check the wires with a volt/ohm meter but I could not figure out how to do it.

[Chryco Psycho]

Set your ohmmeter to 50 k scale , the wires shoudl read between 7-22 k depending on the length

[dpcd67]

WILCO
thanks

[dpcd67]

I set it on 20K, and got 1.2 reading on all the wires.  I have no idea what this means. I think I will just run it; it does run great and will smoke and scream the radial tires for 50 feet, which is not easy to do. From a rolling car at idle.

[HP_Cuda]

What kind of wires are you running?

[dpcd67]

MSD black wires I got from autozone; nothing special.