Hello,I have 08 yfz450 that won’t start. All it does is pop/backfire. Things I have done and checked. Just had head done by shop, valve clearances are set, timing is correct 14 teeth between, lobes at 45s, compression 90, leak test good. TPS unplugged still won’t start, flywheel key isn’t broken, has spark obviously, won’t start if put gas in cylinder which should eliminate carb. Running out of ideas I have tried pull starting as well. I have also swapped cams with no luck thinking gear moved position. I tried cam mod only backfired louder. PSI dropped to 40 when I tried cam mod. Any ideas?