Neighbor's 70 HP

My neighbor's 70 HP Johnson is fouling the center spark plug and don't have any power.
Accordant a good buddy cleaned the carbs and it ran ok. I think there has been to much shade tree guessing what to do without the aid of a manual.
I look at the welch plug on top of the motor to get the model and serial number. The nomenclature plate is missing.
J70TLCCA
G776099
I am betting it is a 70 HP 1988 20" shaft. I will check the link/sync, spark and compression.
Any other thought or suggestions.

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I would check the compression on all the cylinders right off the bat. Go forward from there. Just my opinion.

Ya on the right track Melvin!!

As suggested check the compression and the ignition MR. Hatcher, also look at the overboard discharge hose (pee tube) make sure if it starts low on the port side (from behind) it runs up over the cylinder head before is exits the motor pan.