A fine looking bike. Good job.
I'll make a suggestion; Move the chain tensioner from the engine chain to the pedal chain. On that side it needs to hang upside down.
Adjust engine chain tension by moving the wheel (axle, really) back and forth in the slots. On the pedal side you'll likely need to add enough links to get enough slack for the tensioner.
This way there is far, far less strain on both chains and on the tensioner.