Couple of weeks ago a friend and I took my 912UL powered RV12 out for breakfast at an airport about 100 miles from my hangar. We arrived and the ramp temp was in the high 90s. Went to the FBO restaurant only to find out they were closed for the week. Less than 15 minutes after shutdown we restarted the RV12 and while taxing to the run up area I noticed it appear "sluggish" for lack of better term. As I started to runup for the mag check I noticed the cylinder heads climbing into the yellow, a short taxi back to the ramp and shut down followed. There were no visible leaks, oil level was fine, and so was the coolant level. Also no noticeable fuel in the carb float pans, floats have been checked about 50 hours prior. After an hour of trying to arrange ground transportation home one of the mechanics on the field recommended a restart. We started it back up, all appeared normal and flew it back home with no problem. The local opinion is it was vapor lock. Anyone experienced this situation with the 912UL?