90HP Evinrude has a miss after getting warmed up.

[TPDINAZ]

I have a 1981 Evinrude 90HP, model E90MLCIM. After the engine warms up it starts to miss. It loads up and the only way to clear it up is to run it at full throttle. After a while even that doesn't help. I've changed the plugs, no joy. Anyone have any ideas as to where to start the diagnostics? I have ordered a OMC repair manual for reference.

Thanks,

Tim

 

[racerone]

Start with a compression test.

 

[TPDINAZ]

Start with a compression test.

Are you thinking that low compression is fouling the plugs with unused fuel/oil?

 

[racerone]

A compression test is the first thing to do in trouble shooting that motor !

 

[flyingscott]

A compression test needs to be done first because those motors are notorious for breaking rings. Does the primer ball on the fuel line get firm when you pump it up?

 

[TPDINAZ]

Yes it does. The boat is 90 miles from here. I'm going to bring it down to my home the weekend after 4th of July and start the diag and repair process.

 

[TPDINAZ]

The broken ring thing is starting to make sense. For reference; what should the compression be?