Smokin' 420 SEL

[E150GT]

Hey guys and Gals,

I got an 86' 420 Sel that sometimes when I nail the throttle produces large amounts of what looks like white smoke coming from the tailpipe. It does not smoke on any other occasion the a full throttle downshift that I have seen. I alson have only noticed it a handful of times. The car has about 200,000 mile almost and the heads were rebuilt about two years ago. I have a full engine crankase with clean mobil delvac 15w40 and I dont need to add oil between 3 month oil change intervals. Im not sure if its burning oil or maybe just blowing accumulated carbon or something. Are these engines suseptible to carbon buildup? Should this be a major concern? Any input would be appreciated. Thanks.