Small Engines (Lawn Mowers, etc.): Engine will not start., compression gauge, head gasket

Question
I had asked the quest ot Eric jones.  He had replied with the following question.

Answer:  How did you check the spark?  If you use a spark tester with .166 inch of a gap, most are pre-set, then the ignition is fine.  If you just used the spark plug by grounding to the engine block and see spark then the ignition is probably alright.

What concerns me is that you see spark, replaced the ignition module, but when it does not start on starting fluid then there is a serious problem (maybe).

Does the engine have compression?

__________

My answer is that I had pulled the plug from the engine.  Put the Armature back on the pulled plug and touched it to the engine.  I did see a spark.  I did not use a spark tester.  He asked if the engine has compression.  How do I verify that the engine has compression?

Thank you,
Rich

Answer
For this test you will need a compression gauge. the typical compression reading should be somewhere in the 80 to 100 psi range. If it is testing below this range, the repair may be as simple as a bad head gasket, or it may be that the rings a wearing out, as these are usually the most common problems with low compression.