Clouds of black smoke upon acceleration with black velvet sparkplugs on '86 760T. Car was running very well after I put in new injectors, ECT and AMM, set base idle and did many other things a few months ago. Sparkplugs ran very clean. A few days ago I put a Dawes device set at 10 psi and car ran very nicely. I briefly used the power once or twice but did not abuse it. Last night I took a fist long drive and felt misfire like from running too rich. When I came home I took out the Bosch platinum sparkplugs and they looked like black velvet. This morning I put in a set of new NGK BPR6ES. Took a drive and accelerating in hilly country the car was without power and put out clouds of thick black smoke. All I can think of oxygen sensor. It is one thing I have not changed. Moreover, I put some silicone on a couple of turbo hoses recently to replace them after I did some work on the car. Silicone, I hear, can damage the sensor. I checked the sensor this morning with a voltmeter and I thought voltage change was a bit slower than I remembered, but I am not sure. Any and all help with be greatly appreciated.