Compression and Spark Plug Diagnosis Help

[doubleyellow]

1970 440, stock, fully rebuilt, couple hundred miles since going in the Challenger.

So been chasing a vibration/roughness issue. Idle is OK, but over 200 RPM, engine get progressively worse in regards vibration/roughness.

Checked timing, dwell, plug wires, tuned carb, multiple times. No real improvements.

Although engine fully rebuilt top to bottom, decided I should do a compression test.

Here are the numbers (in psi):

1 - 210, 3 - 205, 5 - 210, 7 - 212, 2 - 210, 4 - 200, 6 - 198, 8 - 202

Hopefully did the check correctly with all plugs out, and throttle wide open

Now here are pictures of the plugs (not 100% perfect focus)

Looking at 1-3-5-7

Here are 2-4-6-8

Overall the compression range from 198 to 212 should be OK, but you guys tell me if that range is OK for a fully rebuilt engine.

What is concerning is that the lowest compression cylinder #6 (at 198 psi), also has the spark plug that is has carbon and not looking normal (or at least similar looking) to the other plugs

I do have an overkill carb (750 CFM ProForm) and engine still running too rich.

Any expert feedback on the Compression data, and, the spark plug diagnosis would be greatly appreciated. Not sure if I need to start digging deeper into the engine to find something, or, I've still got external thigs to chase (ignition, vacuum leak, fuel, etc)

Thanks

 

[Chryco Psycho]

The compression is fine , depending on the mileage you have now the rings & valves could still be seating causing the variance .
The tuning is off , plugs are far too rich , unless you just started the engine with the choke on those plugs should be a light tan . I let the engine tell me where to set timing & never use a light , at 2500+ rpm keep advancing the timing until the rpm stops rising then back it off until the RPM just starts to fall . you should be around 16* at idle with a peak of 36-40* above the advance curve , if you are set anywhere near stock around 5-6* this is not good !
Next you need to fully adjust the carb , float levels first , idle mix then start working on the jetting I would start about 4 jets sizes lower although timing may help clean up the plugs , you will probably have to change air bleeds if the cam is different from factory & makes lower vacuum as well .
How are the vacuum hoses connected , Power brakes should come from the intake runner & test to be sure you don't have a leak in the booster by plugging the port in the intake to see if it runs differently . PCV should be connected to the base of the carb so it is distributed evenly to all cylinders .
IMO the Proforms are one of the best carbs you can buy but on a 440 a 750 is too small , I would use a 700 on a 340 & 750 on a 383 .