2007 Honda 150 power loss

"I've got Honda twin 150s

"I've got Honda twin 150s on my Tomcat
I've been gradually losing power in my port Honda 150... it was only at 75% power when running..It was Idling fine.
They had 350 hrs on the plugs so I changed them all.
It runs fine now...but looking at the old plugs from port engine the # 4 plug was all black compared the others.
On my fuel use computer it shows that now at 20mph my Starboard 150 is using 1 gph more than the port 150(the one with blackened plug)
which means the Port is not performing as well as the other causing starboard engine to use more fuel to take up the slack.

What could be wrong with my port engine?
valve adjustment...fuel injection? ignition coil?

Any advice...help would be deeply appreciated

DickE
Orinda,Ca
"

I would be leaning to a dirty

I would be leaning to a dirty or faulty fuel injector as it is only rich on 1 cylinder. A coil would show up as a distinct miss and the engine would be running rough.

all black means
running rich

all black means
running rich

sticky injector
bad valve seats
in correct valve lash
no spark