Running on one cylinder

[Silence888]

My 98 mercury 4 stroke 50hp is firing on one cylinder, it has spark, compression is 80 psi on all, spark plugs are good, I cleaned the carbs but maybe not well enough and haven't done a vacuum test yet. This outboard hasn't been used in over a decade. Please help

 

[Texasmark]

Fuel varnish or rats in the wiring would be my guesses for starters. Put a new impeller in your water pump. Put new oil in your powerhead and lower unit. Get a troubleshooting manual. Goat to Boat Parts & Accessories at the top of this page and dig around for Seloc manuals. You can rent time online and have a manual in front of you as fast as you can give your CC number. Look in the ignition troubleshooting section.