Once witnessed a 3.0SC that bent valves with a missed shift doing a similar thing as unburnt fuel went to vapor straight out the tailpipe.
From personal experience I had a fuel distributor in a '74 911 I owned develop a pin hole in the metering plate. Looked like a mosquito fogger. UNBURNT FUEL and some blue smoke.
Regarding sitting up for a while:
Years ago I bought a barn find BMW R69S. It has sat for a few years and while it cleaned up beautifully, it did not run.
The gas tank was a mess and I spent 2 weeks cleaning it. Care had to be exercised as the bike was a rare color and the paint was original. Used acid, nuts and bolts and a lot of neutralizer. It was re-coated with a PPG 2 part expoxy product I've had good luck with. FWIW, the coating is now over 15 year old and is still in perfect condition.
The engine had little compression. I loosened all the valves and took a dead blow hammer to the stems to knock off any debris/carbon/rust. Did a complete tune up (points, condenser, valve adjustment, oil change and brand new (now NLA) Bing carburetors.
Pumped 30 weight oil into the cylinders and spent about 15 minutes kicking it over. Re-checked compression and deemed it was enough to get it started. It did start and smoked like freight train while blowing out rust and other debris in the mufflers.
Next came the "Italian Tune Up". I had already decided to do a top-end if necessary but thought the bike deserved a chance. These are very robust machines.
I took it out and ran it up to redline (7,000+rpm) in 1st an 2nd and then cruised in 3rd for a cool down. This was repeated for about a half dozen times.
Rode back to the garage and dumped the oil. Re-filled the sump and rode it for an hour or so. It performed flawlessly.
To this day this bike is still one of the strongest running vintage BMWs I've ever ridden and I've had a few. FWIW: It's with a close friend who considers it one the best bikes in his collection of vintage BMW motorcycles.
AND
IT DOES NOT SMOKE AT ALL