Clean the plug again and switch the plug and wire (if long enough) with cylinder # 2 and drive it again.  ALSO have a really good look at the Cap pickups to make sure it is not damaged in any way.  New parts should always work, but the reality is sometimes they can be defective.

 Regards
Graham

I know a little about everything

I know alot about very little.

Thank You in advance!

Stieve

Grumpy: I'm bettin' The Joker told you to kill me soon as we loaded the cash.
BOZO;The Joker: No no no no, I kill the bus driver.
Grumpy: Bus driver? What bus driver?

Cleaned plug drove 100 miles, plug about as sooty as before. Could cam followers/lifters cause this type of problem? Valve clearance measured correctly-

Thanks, Murray 

Thank You in advance!

Stieve

Grumpy: I'm bettin' The Joker told you to kill me soon as we loaded the cash.
BOZO;The Joker: No no no no, I kill the bus driver.
Grumpy: Bus driver? What bus driver?

Start with the easiest. Dist cap, ignition lead, plug.

1993 stock Tahiti mini ~40k miles, 1275 with the HIF38 carb. I've recently replaced the manifold with a Minispares intake manifold, and a Maniflow cooper style header to an RC40 exhaust. K&N air filter in original filter housing, with holes drilled underneath to allow in more air. New NGK plugs, wires, cap, rotor, 1.5ohm flamethrower coil. Has the original (stock) electronic ignition distributor.

Timing seems good, no pinging, runs sort of surgey but has ok power and pickup, bucks sometimes for no seeming reason, especially when cold (choke setting dosen't effect this much.

The main question though, is that after a few hundred miles, plugs 1, 2, and 4 are light grey with no soot and plug 3 is all black (but dry) soot!  Compression check was 150, 145, 148, 150 (1, 2, 3, 4). The brake boost vacuum is hooked up to the Minispares intake manifold sort of where cylinder 3 is, could that do anything?

 Any ideas of what I should check?