I have an occasional miss in my Merc 1150. It happens at all different RPM's. If I move the throttle a little either way it goes away. I did some inspecting and noticed the wires coming out of the stator have crumbling insulation and the wire inside looks corroded. Could this be the problem or another one?
I haven't had a chance to dig into it yet, but being December in Wisconsin with snow already on the ground I have all winter to look into it. I won't be able to tell if that was the problem until the ice goes out in the spring. Bill
1968jetflite wrote: Did you ever figure out what is wrong with your motor? I believe I am having the same problem with my 1972 140hp merc as well. Any help would be appreciated.
Pull the distributor cap, inspect & clean. I've seen many a cap with "trash" in there and it'll cause a misfire or crossfire. Spray the cap out with carb cleaner.
Note the condition of the spring-loaded carbon center-contact. It should freely spring back when you push it into the cap. If not, it's gunked up. Twist and pull to remove; clean & reinstall.
Run the motor in the dark and see if there are any ign hi-tension wires arcing to ground. Check the spark plug boots for the same.
Clamp an inductive timing light around the coil wire and see if you can spy a misfire. Do the same with the individual plug wires. If it only misfires underway, you may have to have someone in the back of the boat, clamping the timing light on the various ign wires. A "spark indicator" that you lay alongside the wire will work too, but they're pretty faint in daylight and hard to see. Timing light is nice 'n bright and you'll catch any misfire for sure.
Pull the plugs and inspect for an off-color plug. Carbon deposits on most of the plugs but one or more clean-as-a-whistle might indicate the plug(s) being steam-cleaned from a water leak.
How old are the plugs? Those Perma-Gaps are long-lived but they don't last forever. A new set of Champion L76V's or ACV40FFM's might perk it right up.
I have replaced the plugs a couple times in the last couple years to see if that helped. First with Champions, then with NGK's. No change. I was going to check the cap when I tear into it to repair/replace problem with the stator. Thanks for all the help. We are all very lucky to have a site like this with the knowledgeable people and professionals such as yourself to be willing to help.
Take a close look at your coil.
I believe it will be the small black coil - not the earlier, invincible red coil.
Check the coil for cracks, which cause sporadic misfiring under different levels of load.
Doc has a good point, those smaller coils are more prone to cracking than the old Dinosaur Orange/Red coils that mount in the cowling. Pull the coil off the crankcase cover, peel the rubber back a bit and check all over for cracks.
The orange coils found on Merc Twins and various 3, 4, and 6-cyl ADI models have a really nasty habit of cracking. The diagnosis will drive you Nutz!! Cheers.........ed
I will check it out when I get a chance. Right now I have a few extra things stored in our garage until next week when our son closes on his house. And also the Mississippi is a little hard up here in Wisconsin this time of year, so I am going to wait until after the holidays to dig into it. I have until about April to be able to take it for a test ride after the ice goes out, so no big rush.