'94 200 Mercury missing

garbubba · #1 10-14-2013, 06:47 PM

Had a great day out on the boat today, ran 25 miles out (&back!) but when I slowed at the launch she was missing, not like i've heard before. It was irregular, not one cylinder I'm pretty sure, no smoke. Put it up & brought it home, when I flushed it it was still missing, not bad, but missing

Where do I start to trouble shoot this one?!

Plugs first?

I've been through the entire fuel system recently.

Replaced both power packs two years ago.

Thanks in advance,

Doug

spareparts · #2 10-14-2013, 07:53 PM

as always, start with a compression test. Then check to see which cylinders are not firing

draglink · #3 10-15-2013, 07:13 AM

mine did this one weekend this past summer. Mine is older...right around early 90s I think. Anyway it was one of the boxes on the side of the block(there are 2, one mounts on top of the other). Not sure what they are called.....ignition box, ignition module something like that

phatdaddy · #4 10-15-2013, 07:37 AM

happened to me one time also, turned out a spark plug boot popped off. (easiest fix i ever had on a boat)

1224bret · #5 10-15-2013, 08:50 AM

Check to see which cylinders are misfiring if your sure its not fuel related then check plugs or replace if needed if you still have the issue then if it's only one cylinder it's probably a coil if its one full bank it's probably the switch box for that bank (the two boxes mounted on the right side of the engine one on top of the other) one switch box controls one bank the other controls the opposite bank. If its two cylinders on separate banks then its probably the trigger or trigger wiring. (The trigger is mounted under the flywheel) I've seen a lot of older mercs with broken wiring right at the trigger. The trigger moves and advances the timing when you move the throttle over time with it moving back and forth the wires break. You can repair them sometimes if the aren't broken to high up but it's a temporary fix. If it were no fire on all cylinders it would be a stator issue but that's obviously not your problem.

1224bret · #6 10-15-2013, 09:24 AM

Do a compression test first but if ign and compression are good and your sure your fuel system is good it could also be a broken reed valve or reed valves not sealing properly. They will cause more of a issue at idle speed than full throttle. And they can make a odd noise if not sealing right because you will have some crank case pressure coming back though the carb/carbs effected. Just something else to check if all else looks ok.

draglink · #7 10-15-2013, 02:02 PM

switch box....that's what they are called! Thanks bret!

1224bret · #8 10-15-2013, 07:09 PM

No prob man after busting knuckles for years on my old bass boat I got awful friendly with the merc terminology

garbubba · #9 10-15-2013, 10:29 PM

I replaced both switch boxes a few years back. Half the engine would just quit, then come back. All I got done today was a good scrubbing of the boat & I split some firewood.

I'll get on the motor tomorrow, thanks for the input!

Doug