Urgent!!Beta 250rr engine trouble help!

Hi all, I recently did a top end rebuild on my beta 250rr 2016 (replated barrel and new piston). After running it in, it was running and starting perfect, but after the fifth time riding it she just bogged and died. Electric start wouldn’t start nor would kicking. Tried everything inc cleaning carb and checking electrics and eventually I bump started her on a hill and she rode okay.. but while ticking over I noticed a bit of a rattle, she now won’t start again! Any help appreciated, I’m planning on racing this weekend so I’m trying to fix it before then. ??ANYONE have any help... getting desperate!