B.A.R.T. perpetual motion model...methane from the exhaust routed into intake>combustion>exhaust>intake ?

Sorry, but it won't work. All B.A.R.T. models come equiped from the factory with cranial/rectal insertion as standard equipment.

Problem is, exhaust is mostly CO2. CO2 doesn't burn. If you recycle it once, you might have some unburned fuel left that will still burn, but probably not. And definitely not an infinite number of times.

The problem with perpetual motion engines is, there's energy loss every time it runs. If you're using a fuel, you're taking energy from the fuel to move the engine. The exhaust doesn't have the energy in it anymore. And no engine is 100% efficient, so you're always losing some energy. I think most engines lose about 90% of the energy from the fuel as heat. Only about 10% of the fuel's energy actually goes to running the engine.

I thought all B.A.R.T.S used Fred Flintstone Manual Foot type of motion measured in "Foot Pounds" instead of Horsepower !!

You know he thrives on all this attention, right ?

Get over him or get a room.