How do you do a compression test on a 1985 140 hp Johnson outboard.all spark plugs out? Ground the tester?

Answer 1

If the compression is within specifications, then there is no need to do a second wet check. Make sure you ground the plug wires for safety so as not to ignite any gas fumes!

Answer 2

To do a compression test, there is no ground on the tester. It should have a threaded end on it. You just screw the tester into the hole where the spark plug goes, turn it over a few times, record which cylinder you are testing and write down the test results, then do the same thing for each cylinder. You need to know the correct specks for that engine in order to know what psi you are looking for.. Good luck to you.

Answer 3

go to your automotive store and buy a compression gauge. ground all 4 plug wires to the engine. install the gauge in a plug hole and spin the engine 4 or 5 turns. you need 100# to be good. also, the dodgeman is right, no more than 10-12# difference between any 2. do all 4.

Answer 4

no,,you need to screw the hose part of the gage in to the cylinder that you want to check,and crank the engine over several times,and the look at the reading,also do a wet check on it,this means take out the gage,and then squirt a small amount of oil from a can in to the cylinders,and do the test again,and compare the readings, do this on all the cylinders ,and then compare all of them,they shouldn't be more than 10 pounds difference in any cylinder,and if there is ,somethings wrong on that cylinder,the wet check will boost the compression a little,that's why you need to do a wet and dry check on it, then compare all of them,good luck,i hope this help,s.

Answer 5

agree with above, but make sure choke and throttle are wide open, ground ign wires, dont create sparks around plug holes or flames may shoot out!