What is the model number of that engine?
Is this a engine you've had and used for some time... OR... is it new to you?
Has this engine been sitting for some time?
Some history on the engine is needed.

First step is to remove all spark plugs, then to take a compression check. What is the compression psi of the individual cylinders?

Second step is to take a spark test. You can purchase a air gap type spark tester at most auto parts stores. or easily build the following. The spark must jump a 7/16" air gap with a strong blue lightning like flame... a real SNAP!

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(Spark Tester - Home Made)
(J. Reeves)

Most auto part stores have "air gap" spark testers... OR..........

You can use a medium size philips screwdriver (#2 I believe) inserted into the spark plug boot spring connector, then hold the screwdriver shank approximately 7/16" away from the block to check the spark or build the following:

A spark tester can be made with a piece of 1x4 or 1x6, drive a few finishing nails through it, then bend the pointed ends at a right angle. You can then adjust the gap by simply twisting the nail(s). Solder a spark plug wire to one which you can connect to the spark plug boots, and a ground wire of some kind to the other to connect to the powerhead somewhere. Use small alligator clips on the other end of the wires to connect to ground and to the spark plug connector that exists inside of the rubber plug boot.

Using the above, one could easily build a spark tester whereas they could connect 2, 4, 6, or 8 cylinders all at one time. The ground nail being straight up, the others being bent, aimed at the ground nail. A typical 4 cylinder tester follows:

..........X1..........X2

.................X..(grd)

..........X3..........X4

Let us know what you find.

Hi thank you. Yes this engine has been used every year for commercial fishing

Hi one cylinder compression is lower than the other a friend have the engine at his house soo I'm asking him going on with the engine

Hi can you please send me drawing of your spark plug testers

That tells me nothing.... I need the actual compression readings. No, I don't have a drawing... if you can't build it, they're available at auto part stores.