Toro V-twin backfires, does not start when hot

[dtestin]

2015 24.5hp Toro Loncin 708cc engine, 240 hrs. Backfires, does not start when hot. Gas was fresh. Cleaned carb and it was clean inside, don't seem to be any adjustments. Coils seemed to be good using an inline tester. What else should I be looking for? Vacuum leaks? There are a couple of black plastic nipples that press into the top of the carb. What do those do? They have small green o-rings on them.

 

[Rivets]

Two things I would check. First is the valve clearance. Second would be coil air gap. This manual goes through the procedure. https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&ved=2ahUKEwiph6K-7sGEAxVqg4kEHRFaCWsQFnoECCMQAQ&url=https://www.tractorforum.com/attachments/loncin-v-twin-pdf.70838/&usg=AOvVaw0WcGZ7va_PJRH_ChYA7sRR&opi=89978449 One thing I should add, make sure the choke is wide open.