2002 Mercury 75 Carb Question

[Hvymtl]

I have the top cylinder not firing at idle and to about 1/2 throttle -- at half to full it runs fine. Turning the low speed screw in/out has no effect on engine. Can I assume the carb only needs cleaning or can there be electrical gremlins causing this? I have cleaned and rebuilt lots of cars and motorcycles - should this carb be any different?

Update: plugs are new and gapless. Top plug was extremely wet when I pulled it but others didn't look much better.......

 

[enginepower]

I had similar issue on my 90. One of the triggers ohmed within spec but would intermittent lose fire at idle. Replaced it and has fire at idle now. Go here for spec on checking your trigger wires.http://www.cdielectronics.com/support/ Really supposed to check DVA voltage on them but if you have one that ohms way different than the other 2, need to replace the trigger.

 

[Faztbullet]

Your motor has CDM modules and it sounds like one is bad, the way these work you need the CDI testing manual as the one not working can be good and another that is working be bad effecting the one not working.....confusing huh??

 

[Hvymtl]

Really confusing - guy I bought it from said carbs were rebuilt...so if he was telling the truth, Then the next step would be to check the CDI/CDM.

So this module failing would work fine at mid to high speed but not idle??

 

[Hvymtl]

Is the CDM the coil pack?