25hp not running full speed

[pulledabill]

Early 90s 25hp Merc 2 stroke. Always ran 25mph with me only and 20mph with buddy. Ran fine when put away with fuel stabilizer during winter.

Added Perko switch, new lower unit oil and added elect troller few weeks ago. All seemed fine when I backed in to ramp few days ago just to run it. Added 3 gallons of fresh fuel before heading over to lake Thursday. Trolled only with gas motor that night. Friday morning it ran a bit rough so I put out wind socks to run higher RPM. Ran in full thottle but could only get 9mph out of it.

Checked plugs looked okay but ran into town for fresh plugs and some additive.

Started and idled great and no wind socks needed. Throttled up and same issue of only 9 mph. Fuel filter looks good.

Thoughts and ideas?

 

[racerone]

Check spark.-----Sounds like it is running on 1 cylinder.

 

[pulledabill]

Just checked spark which was good. Backed in to ramp by house and disconnected 1 plug at a time which resulted in poor idle of course but it ran. Checked primer bulb in bucket of water which showed no air bubbles.

 

[racerone]

Does spark jump a gap of 3/8" or more on both leads ?----Checked fuel pump diaphragm ?---Checked flywheel key ?