1988 Mercury Black Max 135 hp compression

kimcrwbr1 said:

Do a decarb on it first before you do anything else. Get a can of seafoam spray and take it on the water and bring the engine up to tem first and at a high dle speed spray seafoam into the carbs until it starts smoking real good and quickly shut it down. Wait half an hour and then point it toward the big part of the lake and run it WOT for about 1/2 an hour and then see how well it idles. The compression should be within 10% between high and low numbers and your just a little above that. After the engine fully cools down then do the compression test again 1-6 1-6 1-6 and use the high numbers for each cylinder. Allways check compression engine cold and three times through to account for any mistests. Make sure the battery is fully charged and the spark plug wire are grounded to prevent damage to the switchbox. Does the engine start and is the engine misfireing is the question you cannot diagnose a misfire it it has not been started? A spark gap test with a spark gap tester will eliminate the spark variable but the cylinder drop test will identify a cylinder that is not firing.

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