Um I dont think the pull start slipping would imitate loss of compression.
When a pull start goes bad they are usually intermittant. In that a pull may turn the engine over a couple of times then slip through the remainder of the pull. Or Turn over, slip, Turn over, slip etc.
Its not a unoticeable thing, this is when a lot of people cut up the fingers because the bearing is letting go then catching.

If the pullstart is in good order and there is very little compression you should still hear the motor rolling over, no matter how much loss is there you should still get friction from the internals.

If there is some compression you should get a good plop plop plop plop plop when you yank the cord.
Thats the compression stroke.

Just like on a dirt bike when you kick it over. Dirt bike is simple test, put thumb over the plug hole and compression will bump your thumb right off. Same shows true on R/C engines however its of course much less pressure.


Dbow