Re: Read these spark plugs...
On the street there is a long old argument whether to run an open or closed spacer on a dual plane. The major DIS-advantage is a little less low RPM throttle response while upper RPM power may have a slight increase as each cyl can 'see' more carb.
If it was advantageous, Merc engineers would have done it.
As for the plugs, lay them ALL facing the sun to get a better pic.
They look very close to just fine.
Curious, is that a "Marine" Performer? It shouldn't need any spacer.
A very old street racer trick to gain more complete combustion is to add a 1 inch closed spacer with a double gasket underneath with window screen between the gaskets. The theory here is at WOT fuel is literally a steady stream pouring in. Flowing thru the screen the fuel is forced to break into smaller streams/droplets sooner, thus forcing the fuel to disperse quicker and better atomize with the air. better atomization, better combustion, more power. No more RPM but quicker acceleration to WOT.
Edit; One benefit of this installation is reduced possibility of a back fire/carb fire. Fire can NOT rise thru a metal screen, it is contained within the intake and quickly burns out or is suffocated.
CAUTION, ALWAYS check to be SURE throttle plate have clearance to the screen as the throttle will stick if contact occurs.
