2000 200hp evinrude ficht surging/misfiring under load

[searay2003]

Hey all, I have a 2000 200hp evinrude ficht I just picked up. engine starts and idles fine. When I put the boat in the water as soon as I shift into gear putting the motor under a load it starts to kinda surge or misfire. I've ran a diagnostic and there are no faults. compression in all cylinders is good. I indexed all new spark plugs and after I ran it for a bit I pulled the plugs and the one on cylinder #5 is clean and looks covered in gas. the rest all have black soot. What could cause this?

 

[racerone]

Check for spark on #5

 

[searay2003]

Check for spark on #5

I should have added that, it has good spark

 

[searay2003]

one other thing, when I take the intake cover off, when running all of the other intakes seem to have good suction. What I think is #5 seems to blow air out of the air intake

 

[faztbullet]

Blown reed block gasket or cylinder scored

 

[RoyceLiving]

But what causes the surging? I am having the same issue with a Suzuki 140. Starts and idles fine, but at about 50% throttle, it starts this surging high rev, low rev, high rev, low at a very fast frequency. Like for iterations per second.