80s mercs run half speed at first

[Nickstoyz]

Hello, so two outboard same problem . A 25 and 35 hp. First start of the day, starts right up and sounds great. go to give throttle and maybe only get half power at wot. The motors sound ok when doing this but no power. Turn them off to fish for a bit start back up no change. After a while of running they will spudder or studder and you can hear that the engine wants to go fast then just like that the motor runs great!! New plugs. Fresh gas. This is the best way I could explain it. short version of above is like they run on one cylinder at first then just like that two cylinders. I guess I should mention that they both run great with muffs. I'm lost.

 

[JDusza]

Sounds like not running on all cylinders. Do a spark test with an air gap spark tester and look for spark to jump 3/8" gap.
With the engine running and with insulated pliers, pull one spark plug wire at a time. If cylinder's ignition was working then engine will die. If ignition is not working, there will be no change in engine sound.
Runs great on muffs because there's no load requiring power...
If you have ignition everywhere then you could be looking at fuel starvation.

 

[Nickstoyz]

Thanks JD! I will check that. And what if it is an ignition problem? CDI?