2005 200 hp Merc; Dirty Carb?

When the motor is cold, it starts fine, idles fine and has plenty of power taking off. While running comfortably at 5000 rpm and 45 mph, after several minutes the motor clearly starts "jumping" (i.e random, quick bursts off power every couple of seconds). Sometimes when this happens I can hear definite "knocking" in the motor. After a minute or two of "jumping", the motor then will only run at 4000 rpms and 35 - 40 mph. While running at this reduced speed/power, it rarely, if ever, "jumps". I've checked plugs/wires etc. I ran some fuel injector cleaner through the motor and that helped for a couple of short trips, then the motor starting "jumping" again. It almost always runs great while cold. Does this sound like a dirty carb issue? Could it be a coil randomly misfiring? Other suggestions?

Re: 2005 200 hp Merc; Dirty Carb?

Any thoughts on this issue would be greatly appreciated. I've never taken carbs apart before, but I'm willing (and able I think) if it sounds like that may be causing this problem. I've removed the carbs, partially taken them apart and sprayed carb cleaner throughout and I hope to take the boat out today or tomorrow for a test run. If the problem continues, and if someone with more knowledge/experience thinks this may be caused by a dirty carb, I will attempt the total carb cleaning (removing jets etc).

Re: 2005 200 hp Merc; Dirty Carb?

Fill out the profile.Always put in the serial# along with the make and model.
First do a compression and then a spark test.If they are OK.
You have inline filters or fuel/water seperating filter?Change them.Then start with the fuel pump.Get a rebuild kit.
Then start taking the carbs apart.The jets might be clogged.
Check for soft hoses and crap in the system.
Ethanol is messing with a lot of motors.J

Re: 2005 200 hp Merc; Dirty Carb?

Thanks Jerry! I dont have the serial # with me now, I'll add that info tomorrow. I hope to run the boat today since I made a "preliminary" carb cleaning this weekend. I'll post additional info tomorrow.

Re: 2005 200 hp Merc; Dirty Carb?

serial number is 0T922318 I was not able to take the boat out yesterday. I'll run it today and HOPE it's okay!

Re: 2005 200 hp Merc; Dirty Carb?

Sounds more like a electrical problem such as a bad CDM module or a defective trigger....

Re: 2005 200 hp Merc; Dirty Carb?

Are you using a fuel/water separating filter? If no, then

You could have enough water accumulation in the tank that it is sloshing and picking up a small bit of water while running at speed, the motor 'bucks' when the drops are sucked thru the carbs.

If everything checks out tilt the craft on the trailer such the fuel pick up is on the low side. Let it sit a couple hours to settle, pull a fuel sample and look at it.

Re: 2005 200 hp Merc; Dirty Carb?

Latest info: after semi-cleaning the carbs (removed them, took them partially apart and sprayed with carb cleaner - no float or jet removal) and replacing all plugs, I took the boat for a brief run yesterday. Started great, idled for a few minutes with no problems, had GREAT speed out of "the hole", cruised perfectly at 5000 rpm / 45 mph for several minutes. I then slowed down to idle through a shallow water area for a few minutes. When I took off again, there was not as much power out of "the hole" and it would only cruise around 4200 rpm / 38 - 40 mph. I ran it a few minutes at that speed and, while it did not "jump" like it was before, there was still some loss of power. Before the semi-carb cleaning / new plugs, after the warm up phase, it would only cruise at 4000 rpm, so I've gained a little power. Does this sound like a more extensive carb cleaning may be needed or some other issue? I do have a water seperator filter and that was replaced when I cleaned the carbs.

Re: 2005 200 hp Merc; Dirty Carb?

Faztbullet: I'm not familiar with a lot of the lingo: what is a CDM module and a trigger? How would I test those? When the motor is "jumping", it does feel more electrical than fuel related because it is such a noticeable, quick "jump." Could a coil be going bad and working intermittently or a spark plug wire need replacing? Since the motor almost always works perfectly when cold and the problem occurs as the motor warms up, I suspected maybe fuel flow issue that is masked when the primer bulb has been used to increase the fuel temporarily. I desperately want to fix this problem before it leads to bigger issues!

Re: 2005 200 hp Merc; Dirty Carb?

CDM"s are (CAPACITOR DISCHARGE MODULES) or the little black box with coil wire as customers call them. The trigger is under the flywheel and tell the CDM when to fire. You need a timing light and a good ohm meter to troubleshoot the problem. First make the problem happen and then test to see if it has lost spark (with timing light) and on which cylinders. Then you can test the affected CDM's and trigger to see if they have problem.