Are the spark plugs removed? If not, it's possible you could have liquid in one of the cylinders, causing a hydraulic lock. Recently, I've been using a very nice little borescope that plugs into a USB port on my laptop, and it gives a very clear full-screen view of what's going on inside an engine. The probe will fit into any hole that's at least 5MM in diameter, even a .22 caliber rifle barrel. Going through a spark plug hole gives me an excellent view of a cylinder and there's even a 90 degree mirror available to attach to the lens. I've also used it through an oil drain plug hole to inspect a crankcase.
The nice part- - - -the whole setup is available on Ebay with a CD setup disc to interface with the computer and only cost $35.00!
Jerry
