help. i have compression gage,need to know the procedure to go through.checking comression on 1987 mercury,45 hp .. thank you very much

Quick and dirty description:

Remove all spark plugs. Screw compression testing guage into one cylinder, have a friend turn the motor over 4-5 times, record compression, reset guage, repeat on next cylinder, until all cylinders are checked.  Depending on your motor, you may need to ground the spark plug wires to prevent damage to your ignition system.

There is also a "wet" compression test, where oil is sprayed into each cylinder, to see if compression increases dramatically over "dry" test, indicating a "blow-by" condition.

Techs also use "running" compression tests, and "leakdown" tests.

There are a number of causes of low comression; I'd suggest you get a manual for your motor. It will explain not only how to do the test, but how to troubleshoot the results.

Remove spark plug, insert the gauge, trip the emergency shut down(safety kill switch), open the throttle, crank the motor over, read the gauge, replace the plug and move to the next cylinder. If you don't have the kill switch then just remove all the plug wires. If you want to go a little farther then squirt a few drops of oil in the cylinder after the inital compression test crank the motor over a couple of times and check the compression again and compare the readings, if a significant difference in these readings (between 10-15%) would indicate worn rings

thanks guys for your reply ,i will post what i find ,may need more help,,,bassman101,GETTHENET

On a two stroke, you should also have the trottle wide open and make sure your battery is fully charged.  You will also probably find that if you take all the plugs out, the starter bendix will keep kicking out every time it hits on the cylinder with the guage in it.   I most cases,  you will find if you only remove one plug at a time and put you guage in that hole it works just fine.  I usually like to make six hits on each cylinder I'm checking.