CM570 compression in fuel

[Rawze]

Things that come to mind...

* Bad Injectors.

* Leak in fuel lines (pressurize fuel tanks to 10 psi and see if it clears up).

* Cracked or worn out head.

* Bad fuel pump that is sucking air.

It is normal to get some bubbles into the return line. It is due to cavitation at the regulator. -- It will usually stop if you pressurize the fuel tanks a bit.

Have you boroscoped the engine while the injectors were out? -- Check for cracked valves, head, and signs of washed out cylinder walls or washed out carbon ring.

Also check temps at exhaust ports. that will usually reveal a lot too, and run the engine on only one cylinder at a time to see how it does.