Spark Plugs that wont Foul Out?

[medicinal motorcycle]

My bike keeps fouling out the #1 and #4 spark plugs. I just overhauled the carbs with complete carb kits and set the fuel adjustment screws underneath the float bowls at 1.5 turns out, so I do not think it is that. There is no sign of oil in the combustion chambers either. I am using the recommended NGKB8ES spark plugs. They will only last for about a day, then they will foul out and the bike will run like crap on the other 2 cylinders. Sometimes cleaning them will temporarily fix the problem, but usually I have to buy new spark plugs. Is there a spark plug I can buy that will not foul out until I can figure out what is causing the problem? thanks

[Nibblet99]

When you say they're fouling, are we talking

1. A black sooty residue (caused by either a fuel rich mixture, or a weak spark)

2. A grey ash colour (I think this is caused by burning oil)

3 A blistered look? (caused by a weak fuel/air mixture)

Assuming the case number 1...
a) Are the leads running to the spark plugs looking old? - old leads loose there electrical insulation, causing some of the energy which should go into the spark plug, to leak to earth instead.

b) I believe the screw only really affects idling revs. if you dismantle the carburettor, on the needle there should be a clip, which if you move it up the needle (point of the needle facing the ground) will weaken the fuel air mixture when the throttle is opened

Assuming the case number 3...
do the reverse of option b, above