It’s all in the timing
The long start lane on the Red layer is to offset the first delivery of Carbon.
The 4th loop rotates a complete Methane molecule; I’ve tried to grab it just before, but had to settle for this solution.
The Blue-layer sync-loop also keenly timed to be just in time to grab the molecule and deliver it to the exit port.
With a 34 symbol 518 cycle reaction, it’s on the ‘cheap’ side, which is good, but I feel there’s still room for improvement.