What is the compression supposed to be on cylinders. On a 97 Mercury 40 hp 4 cylinder? 
 

thanks,

More importantly, the compression should be "close" between all the cylinders.

 

 

Karl

 

Here's a general compression check answer:

 

A compression test reveals the condition of your engine's valves, its valve seats, and piston rings and whether these parts are wearing evenly. Healthy engines should have compression over 100 psi per cylinder, with no more than 10 percent variation between the highest and lowest readings.