Mercury motor bogs down under load

[jonesn4fun]

Motor: 1996 150hp Mercury Offshore

What the boat is doing:
Cranks up no problem. Idles no problem. Put it in gear and idle out of the marina no problem. Coming out of Marina, when I get out of no wake zone and give it some throttle, it gets up on plane no problem and runs great. It will continue to run fine until I drop down to an idle or stop and turn the boat off to say fish. Once I do that, when I put it in gear try to accelerate it bogs out. Sometimes it stalls out. If it stalls out, it will start right up with no problem, and will idle no problem. I can put it in neutral and rev the engine up and it revs to high RPMs no problem. I can put it in gear and give it throttle to about 1,500 RPMs and it goes fine, but as soon as I try to raise the RPMs above around 1,500, it bogs out. I used to be able to work the throttle by getting on it and backing off, multiple times in quick succession to get it up past that point. Once it gets past that that point it will run great until I bring it back down below 1,500 RPMs. I had the carburetors rebuilt thinking that may help, but it actually seems to be worse as I can?t seem to work the throttle back and forth to get it past his situation now. Also, once the problem starts, I can turn the boat off for 15 mins and when I start back up, it still has the issue. When it does run, it seems to max out at 4,500 RPMs.
What I?ve had done.
1)Tuned up / replaced spark plugs
2)Verified good compression in all cylinders
3)Replaced Fuel water separator
4)Replace inline fuel filter in motor
5)Rebuilt the carbs (3)
6)Rebuild fuel pump

Any ideas would be greatly appreciated.


Thanks.

Dave

 

[racerone]

Open low speed mixture needles 1/4 turn.

 

[dpmsgeek]

racerone, Do you mean from where they are now or from seated?

 

[racerone]

????------From where they are now of course.

 

[jonesn4fun]

I'll pass that on to the mechanic. Thanks.

 

[jonesn4fun]

I do have a follow-up statement/question on this.

I arrive at my boat and start it up when it's cold. It starts right up. I usually let the motor run for at least 5 mins before I pull away from the dock. At that point, I drive the boat for a couple of minutes (maybe 5) out of the marina at a low RPM through a no wake zone. After clearing the no wake zone, I then give it throttle and at that point it's able to get into a higher RPM and into a WOT. It's after running it at WOT for a period of time that the problem occurs. And once it occurs, I've had the motor turned off for at least 15 mins fishing, and when I start it back up, it still has the problem. So I've never experienced the problem when I first start out for the day, it's only after running it for a while.

So I guess my question is....is there a motor temperature condition that would cause an issue if the low speed mixture needle wasn't adjusted correctly?

Thanks.

Dave

 

[SoCalBoatGuy]

This kinda sounds like DJ Alaroona's boat. He ended replacing the floats in the carbs. http://forums.iboats.com/forum/engi...41-very-​frustrated-need-help-with-this-motor

 

[DavidMoore]

I do have a follow-up statement/question on this.

I arrive at my boat and start it up when it's cold. It starts right up. I usually let the motor run for at least 5 mins before I pull away from the dock. At that point, I drive the boat for a couple of minutes (maybe 5) out of the marina at a low RPM through a no wake zone. After clearing the no wake zone, I then give it throttle and at that point it's able to get into a higher RPM and into a WOT. It's after running it at WOT for a period of time that the problem occurs. And once it occurs, I've had the motor turned off for at least 15 mins fishing, and when I start it back up, it still has the problem. So I've never experienced the problem when I first start out for the day, it's only after running it for a while.

So I guess my question is....is there a motor temperature condition that would cause an issue if the low speed mixture needle wasn't adjusted correctly?

Thanks.

Dave

Possibly, but on an outboard more likely to be electrical than fuel related. (just my opinion)

Another way of looking at it is; the more fuel you suck out of the tank, the worse the problem gets. When the problem occurs is the primer bulb getting soft? Have you checked the tank is venting properly, the strainer in the fuel pickup (if fitted) is clean, and no pin prick holes in the pick-up tube.

 

[Chris1956]

If the boat runs fine at high speed for a time and then bogs down while still running at high speed, it is likely a heat related ignition issue.

If she runs fine at high speed until you shut her down, and then she bogs upon restart, it could be fuel or ignition issues.

​Your first post indicated the former. Is that still the case?

 

[jonesn4fun]

The boat runs fine at beginning of day before I run it at high RPM. In other words, I run it under 1,500 RPM coming out of marina then accelerate and it gets right up to high speed without problem. It runs great at high speed and never bogs out. After running for a while at high speed, if I bring it down to a stop or low RPM, then try to accelerate it bogs out while trying to go over 1,500RPM. I can run it under load at up to 1,500RPM no problem. If I'm able to get it past 1,500 RPM, it will run fine again. Also, I can put it in neutral and rev it up no problem. The problem seems to happen under load.

 

[Chris1956]

Well, adjust the carbs to richen the mixture as was suggested. If that doesn't fix it, you may have a heat-related ign issue. It probably makes sense to take a spark test when she is warm and bogging.

 

[JDusza]

Deginetly runnng lean and is starving for fuel at throttle up. Also, throw in an additive like SeaFoam or Techron. Cheap and can't hurt.
J

 

[LEE MICHNAL]

Thanks David for the info