Did you ever run it hot during those three gallons? Associateds run hot you really have to stay on top of the with a raytech gun or comparable . I think you might of lost your pinch when she gets good n warm. The cylinder expands with heat it might have enough compression to crank when you cool a little but looses it when heated up. Thats one thing to keep in mind after you have tried & checked every thing. Mine was always running hot even adjusting on the needle "Richining it up" that led to premature wear and the same thing your going throug. When it dies right away turn engine over chech for compression if it spins considerable with out much resistance , Start looking for a new engine. I ve had a bunch of OS Engines, 12 cvrs hold needle settings good not always chasing them with heat gun, they have almost 1 Hp. They are great for racing with . 12 & 15 cvx's are good sport engines with same reliability but not near the power of the cvr 's HOPE THIS HELPS THANKS