Long story short the piston ate the*cylinder*walls. Took jug off, replaced with over sized piston and had jug machined to new piston. Got it all back together and crank timing is kicking my tail. I turn the 17mm bolt on the crank to the TDC timing mark per service manual, set cam to straight up to align with*cylinder head*mark andinstall timing chain. When I crank it it will back fire and not hit a lick. Not even hit good one time. Spark is good. Carburetor is brand new. I’ve checked TDC with a straw to see if*flywheel*keyway is there and it is where it should be. What am I missing?