Yamaha Wr400-444 big bore crankcase oil

Ok so i figure i would try my luck with you all. My story is a 1998 wr400f with a full new top and bottom rebuild including Lukes Racing 444 big bore kit including piston, rings,replated and honed cylinder, remachined head, new valves and wiseco bottom. Also needed to replace one of my hotcams.

So long story short, after all this work, done at mechanics and machinists, not myself ha ha, my bike now backfires hard on starting and i have excessive oil blowbye out of the crankcase breather? Any tips on where to start. Spent a decent amount of cash on this rebiuld and wasnt expecting to come out of this with more issues.

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