912 uls bing 64 issue

Yep, you definitely want to get rid of your winter blend mogas before flying in hot weather.  Summer blend should be just fine in most applications, though.  I'd think you'd have to have a pretty big under-cowl heat issue before requiring 100LL would actually become necessary.

I have come to believe that operating the RV-12 when OAT is over 70F with winter blend fuel is likely to be problematic. 

We use auto fuel with 10% (actually only 6% - 7%) all year long in Arizona. Temps right now are 110F.
80F  for lows. We have several RV12’s and many LSA aircraft and we all use it.

See if this helps,

Try taking off shallower, less flaps and faster and don’t sit a long time trying to pre-flight and taxi.

Have made 3 more flights this past week with 95 degree heat and now using a mixture of 100LL and Shell nitro which checks at 10% ethanol.  No issues to report.