Engine was not running above 3100 rpm under load so I broke it down and rebuilt the fuel pump and all carbs. It’s a 2004 90 hp 2 strk mercury. Fuel pump and carbs were pristine. No debris, no residue. Rebuilt everything anyway as I have never done it and wanted to know how. It appears now the issue is purely that it’s running only on 2 cylinders. Bottom isn’t firing and the plug looks brand new. Switched the plugs around and bottom still not firing. What would be the next part to replace/check? An audible click is coming from the boot when removed from the plug, but it doesn’t appear any spark is making it to the cylinder. All cylinders compression tested fine. Thanks!
spark check to make sure
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OK I was wrong. The bottom cylinder is firing fine. I removed top and middle boots and motor still ran so the bottom is firing. I still don’t understand why the bottom plug looks brand new. I replaced them all a couple months back. The top is black, middle half black, and the bottom is brand new still. The motor now idles too high at about 1100 rpm. I didn’t adjust any idle screws so what could be causing the high idle? Motor too clean now and getting the gas it’s supposed to and I need to adjust the idle down?? I still haven’t tested it under load so I don’t know if it’s still running on low RPM. Any insight on the high idle?
Idle it down with the cables!
running rich on top cylinder
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changing the cable lengths won’t make a difference that i can see as the throttle arm or whatever its called is flush on all bumpers and appears to be in the correct “idle” position. what needs to be adjusted now to impact running rich or fixing the high idle? idle adjust on the carbs or just the idle adjust on the throttle arm?
should be a idle air mixture screw on each carb, unless that motor has the EPA presets
then you can also adjust idle timing to bring down the idle speed.
you also need to synchronize the carbs.
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