View Full Version : 240 Merc is Missing again!

08-10-09, 11:01 PM
2000 Speedster
Ok so heres the low down....
I did some work on the boat to address my engine miss firing under load. I installed Fresh plugs, wires, water/fuel filter, fresh premium merc 2 stroke oil.

So heres how it goes... Got to the lake at 6pm headed out boat was running stronger the ever 57mph (speedo) with 3 adults and 500lbs of ballast... She was running great, we picked up our 4th and headed out to wakeboard.
We wake boarded strong for 2hrs without a single issue when the boat started to miss while on take off with or without boarder being towed.
The missing could sometimes be avoided if you you avoided WOT and slow started, but if you tried to throttle up to turn or plane fast the missing was there but once to plan the boat would miss less frequently and still run 50mph into the wind.
So I need to hear some suggestions on what to check next...

Keep in mind the new parts installed and the fact the boat ran without issue for almost 2hrs of hard boarding..

Im lost and need advice

08-11-09, 04:12 PM
If it's a 2000 then the exhaust hoses should problably be replaced. The hoses can delaminate on the inside and block the exhaust flow. Do the hoses feel soft in any place? They should be very firm from top to bottom. They need to be removed and inspected to be sure they aren't coming apart on the inside. See the photo on the left to see what happens to old hoses. My boat would start fine but couldn't get above 3000 rpm. I checked everything on the engine and was near giving up when we discovered the exhaust hose expanding when I lost rpm.

08-11-09, 04:41 PM
I do not think the hoses are the issue, I will however check them out. Rpms are not my issues though Even when missing Im able to run at 5500-6000 rpms and speeds ranging from 45-55mph its just not as smooth as it could be...

08-11-09, 09:06 PM
Since it was performing like it should after changing the plugs and wires, I would suspect a weak coil, or a coil with a hairline crack in the tower. When you replaced the plugs were there any that looked different than the others? If there was, pull the coil off that fires them and have a good look at the tower. Then do a resistance check and compare it to the others.


08-11-09, 10:57 PM
Ok Aaron... As Coil do you mean the CDM module?

08-11-09, 11:05 PM
One more question...
Why does the boat only miss after 2hrs or more usage?
Do the coils packs get hot and cause this issue...
I mean the boat was perfect and then gradually got worse... but never to a point where we couldnt get to plane and top speed..
Im really scratching my head here and 75 a pop the CDM's are going to again drain the Tower fund lol..

08-12-09, 01:36 AM
When I was troubleshooting my boat the local mercury dealer suggested it might be the stator coils under the flywheel. Sometimes when they get hot they fail after a while. When they cool down they work again. Maybe you could spray some coolant from a can on the coils when it fails to see if the problem goes away. I had found a company that remanufactures the coils in Alabama. I think it was called CDI.

08-12-09, 01:48 AM
See attached.

08-12-09, 01:51 AM
The CDM's don't have coils. The coils are under the flywheel (tower). I understand you need a special tool to remove the flywheel.

08-12-09, 10:22 AM
thanks for all the info... Ill look into this weekend

08-14-09, 01:47 PM
Whats the part number for the ignition coils? having issues locating a good diagram to show me what to do ...

08-14-09, 02:36 PM
On your 240 they actually call them a capacitor discharge module. Part number 13 in this link.


08-14-09, 03:05 PM
roger that!
Im going to inspect them all tonight and see what comes up....
Thanks again Aaron..