That is true for this engine. 426 PSI is the lower limit in the manual.For what it is worth, this is the compression specs for the YM220/222. A little larger than yours but I feel it would be real close to your 186. Specified pressure 568 to 639 psi. Lower limit 426 psi.
There's 3 considerations:
-Manual does not tell you if this is in cold or hot condition.
-The tools for pressure measurement enlarges the volume of the combustion chamber a bit, not shure how much this affects it
-I have no idea how much rpm the cranckshaft is running on the starter motor, if it is too low you wont get the max pressure.
Anyone had a value between 568 and 639 PSI on a compression test...?