Re: 1991 25 merc hardstart + bad idle
Have you pulled thay top plug wire with the engine running? You can remove the wire and see if engine runs any different, if it don't then you isolated the problem to that wire/ coil assembly. If it does change and runs rougher or whatever the case may be then you have more complex problem. For instance, if your confident the bottem plug is the only one firing, and you remove that wire, the engine should die, if both are are firing, and you remove one wire, the engine should struggle. If you pull a wire and theres no change, than thats the one thats bad. Then you need to check the voltage from the trigger to the coil and everything in between to see where the power stops, then you identify the faulty part. And as mentioned before, a compression check would'nt hurt. Engine at operating temps...throttle open and the plugs removed. Pull it about 6 times per cylinder. If you find you do have good spark, and the ignition system is good.....tune her up....link and sync, carb rebuild.
