86 Mazda B2000 Carbon Build up on Spark Plugs

I have a '86 Mazda B2000, 2.0L. I recently rebulid the engine, new rings, head job, main bearings, red., alternater,carb., and fuel pump. After all of this I continue to get carbon deposits on my spark plugs.

I have tried putting some B-12 in the gas tank on three differnt occasions, no help, I have also put some sea foam in the carb. and gas tank.

My bother told me that I might be getting to much gas in my carb. I have now Idae what is going on, could some one please help? What color is the carbon build up, whitish gray or black? Also how thick is the build up, thin, thick or clumps? Is it on all of the plugs? Carbon fouling is caused by too-rich carburetion, a sticking manifold heat control valve, or a clogged air filter. Check your manual to see if your carb has a mixture adjusting screw. Some have 'em, some don't. It is possible your jets are worn.

Carbon fouling can also result from low-speed driving and long periods of idling, which keep plug temperatures so low that normal combustion products are not burned off the plugs. In such a case, switch to a hotter plug. Check with the guy at the parts counter. The color of the carbon is black, and it is on all of the plugs. The build up if fairly thin, because I can wipe the pluck with a rag and come of the carbon comes off. Thanks for any help you can give me Stevefl, my carb. does have mixture adjusting screw, but I do not know which way to turn it in order to adjust it.

Is there a way to check to see if my jets are worn.

FYI - The truck had been sitting up for close to two years before I got it back, and I have put about 800 miles on it since, about 250 miles are highway. In addition to what Steve said make sure the choke is coming all the way open when the engine is fully warm.

The mixture screw turns in to lean the idle mixture and out to richen the mixture. Keep the idle speed below 850 rpm when adjusting the mixture. Thanks Venturi and stevefl for you help I will try adjusting the mixture screw tomorrow, and let you know how it turn out. Again thanks for the help.