Fuel fouling (rich/spark) or oil leak?

[boatdude100]

1 and 4 cylinders get black fouled plugs.... almost immediately

I would say closer to sooty ... not wet or shiny

Single barrel Holley carb- 3L/ Compression good-avg 160

Any clues if I should I be looking towards
1) Carb adjustment (previous owner did mess with the settings, but wouldn't this affect all cylinders?)
2) Cap/wires (visually in good condition- spark it supplied at each cylinder but how strong?
3) Timing (can/should I do this myself without engine damage as a first timer?)
4) Engine/valves (valve guides as suggested on this forum (thanks!)

All suggestions appreciated!

 

[boatdude100]

UPDATE:
Pulled distributor cap and found significant crud on each terminal. Rotor tip not great either. Cleaned with screwdriver & dremel carefully and started it up. Still idled rough, after 8 min test run and same plugs were black again!

Swapped witres with Mercruiser 3L. No change

** Do plugs described in first post sound like fuel fouled or oil fouled please?*

 

[itsathepete]

1 single barrel 4 cyl should feed all cylinders the same, but front and back have longer runners so might fill a little better at low speed
2 use sandpaper to clean all terminals on cap and rotor (dremel can work) and make sure all wiring connections on coil and distributor are clean and tight and voltage is consistent when running. replace cap and rotor if you want to be sure or if you don't know how old they are
3 yes you can but you will need a timing light. harbor freight advance timing light will work fine for little money. many youtube videos will instruct you. check initial timing at idle and maximum advance (around 2500-3000rpm) checking timing doesn't change anything. Moving distributor changes timing, don't do it until you know what to do.
4 leaking valve seals typically cause a little smoke at start up but not instant dirty plugs. If cylinders 2 and 3 have intake manifold leaks, they will run lean and 1 and 4 will run rich. Spray carb cleaner around intake manifold connection to engine block when running. If idle picks up/smooths out you have a intake leak. Do it around carb base too to make sure you don't have a carb vacuum leak.

 

[itsathepete]

you can swap positions of plugs in 1 and 4 with cylinders 2 and 3 and see if fouling stays with cylinder or follows plugs. if it follows the plugs, get new plugs. done.