Oil would be bluish or black smoke. Did you notice this after just filling up? Even if it was just a reasonably short time of driving? if so, then it might be vapor lock from a hot tank and cooler gas. I have had this experience with my motorcycles after a fill in the hot summer-no other time. The first time it scared me, huge plume of smoke, then when I figured it out I learneed not to fill the tank to normal fill to give the gas some expansion room. Only happens in the hot summer. I had filled it the night before I took it to work, it had been hot, and I got about 20 miles in when it occurred. It didn't occur to me that what i put in the night before would give me the trouble the next morning, but it did. 2nd time was about 10 miles after I filled it up, again on a hot day. Basically a huge fart, then it died on the road, after sitting a biut it started right up and never did it again.