Merc 150 bogs at 5000rpm

[Rob33]

2001 150 Mercury saltwater Engine runs great at idle to 3500 rpm. when I push it to 4500 to 5000 rpm it bogs down on me. Cleaned fuel lines, carb, new filter, running out of ides. I found a cable running from the back of the engine that didn't connet to anything, picture included. Running out of ideas. Please help. Outboard blues.

 

[j_martin]

Re: Merc 150 bogs at 5000rpm

Carb or EFI?

The plug in the wire indicates it's unused. Could be Tachometer (There's a spare on a dual regulator system) or temp gauge sender.

Bogging at WOT almost always turns out to be a fuel delivery issue. If you persist in running it like that, it will eventually turn into a melted piston issue.

Here's a litany of what it took to fix my inherited problem.

Fuel tank had chit in it, clogged pickup screen.
Fuel filter kept clogging, replaced with Racor 60 GPH system
Fuel pump -- wrinkled valves
Fuel pump -- pulse hose had been replaced with soft (tygon) line.
Fuel hose -- Atwood aftermarket, not big enough.
Fuel hose barb -- aftermarket plastic, not able to deliver enough fuel.
carb adjustment -- couple of floats were a little low.

hope it helps
John

 

[hkeiner]

Re: Merc 150 bogs at 5000rpm

The above excellent list of potential causes will likely solve your problem. You can also consider hooking up a vacuum gauge to your fuel line to either confirm or exclude a range of possible fuel related causes, which might save you some time and expense by narrowing down the possible culprits. The below Mercury Service Advisory provides some instructions on how to do this.

http://www.marinepartsman.com/Mercury-Marine-service-bulletins/Mercury-Mariner/2001/EN_17.PDF

 

[Rob33]

Re: Merc 150 bogs at 5000rpm

Thanks guys. It's a carb. I will try all of that.

What part of the fuel line do you hook the vacuum gauge up to, and how much pressure do you want, 3psi? If it is lower, that proves that there is a air leak?

On the clogged pick up screen, how did you clean it. Do you remove the fuel intake to clean?

On the carb adjustments, how do you know if they are to low and how do you adjust them?

Really, I haven't messed with the fuel pump yet, but sounds like its about time.

Thanks again ,
Rob

 

[j_martin]

Re: Merc 150 bogs at 5000rpm

Thanks guys. It's a carb. I will try all of that.

What part of the fuel line do you hook the vacuum gauge up to, and how much pressure do you want, 3psi? If it is lower, that proves that there is a air leak?

On the clogged pick up screen, how did you clean it. Do you remove the fuel intake to clean?

On the carb adjustments, how do you know if they are to low and how do you adjust them?

Really, I haven't messed with the fuel pump yet, but sounds like its about time.

Thanks again ,
Rob

On the fuel tank, I parked the boat on a side hill and siphoned out all I could get. Then threw in a couple of cans of isoheat and siphoned those out. Just for grins and giggles, I put the whole 3 gallons through a scientific filter, which promply plugged up with a white snot that is difficult to see in the fuel.
You about have to pull the pickup fitting out of the tank to clean it. usually not a big deal, unless it's installed so it won't lift clear, in which case you'd have to pull the tank.

On the vacuum gauge. Look up the link. It's there in detail.

I did it the other way, and hooked up a fuel pressure gauge at the carbs. The carbs each have a threaded hole on both sides to the fuel rail. At least one of them has a plug in it. That's where to hook up a pressure gauge.

Carb Adjustment --- it's in the book.
Fuel pump. ------ it's in the book.

Oh, did I tell you to get an oem maintenance manual. (the book)

hope it helps
John

 

[hkeiner]

Re: Merc 150 bogs at 5000rpm

What part of the fuel line do you hook the vacuum gauge up to, and how much pressure do you want, 3psi? If it is lower, that proves that there is a air leak?

It looks like the link I provided above is no longer active. The website's message is that the site was taken down at Mercury's request. Too bad as it contained a lot of good information. It may come back but in the interim, I attached some key pages from the Advisory below. These may be helpful to you. If you PM me with your email address, I can email to you the complete Advisory in PDF file form.

Please note that while the Advisory suggests the use of a digital gauge (which is pretty expensive), a regular vacuum gauge works just fine and you can get one at any auto parts store for cheap.

 

[j_martin]

Re: Merc 150 bogs at 5000rpm

The clear hose piece detecting small leaks in the suction side of the fuel system is the most helpful part of that advisory.

JMHO

John

 

[Rob33]

Re: Merc 150 bogs at 5000rpm

Yeah, I have the book and have been studying it. You guys are great, thanks for the good info. I will attemp to remove the fuel intake tonight and clean it, and this weekend i'll get the vacuum and start the test.

 

[hkeiner]

Re: Merc 150 bogs at 5000rpm

The attached jpg shows the fuel pressure specs for your motor. The pressure gauge test, as pointed out by j_martin, is also a very good way to test for overall fuel system delivery failure. Some advantages of Mercury's vacuum gauge approach is that you can more readily determine whether such a failure is due to a fuel pump failure, a restriction in the fuel line upstream of the fuel pump, or an air leak in the fuel line upstream of the fuel pump. Just a bit more information but either test is well worth doing before needlessly fixing/replacing a bunch a parts that don't need fixing/replacing.

If the above tests don't show an apparent fuel delivery problem, you might next consider testing for a failed spark on one or more cylinders during engine bog. Just a thought...

 

[DRIFTER_016]

Re: Merc 150 bogs at 5000rpm

Carb or EFI?

The plug in the wire indicates it's unused. Could be Tachometer (There's a spare on a dual regulator system) or temp gauge sender.

Bogging at WOT almost always turns out to be a fuel delivery issue. If you persist in running it like that, it will eventually turn into a melted piston issue.

Here's a litany of what it took to fix my inherited problem.

Fuel tank had chit in it, clogged pickup screen.
Fuel filter kept clogging, replaced with Racor 60 GPH system
Fuel pump -- wrinkled valves
Fuel pump -- pulse hose had been replaced with soft (tygon) line.
Fuel hose -- Atwood aftermarket, not big enough.
Fuel hose barb -- aftermarket plastic, not able to deliver enough fuel.
carb adjustment -- couple of floats were a little low.

hope it helps
John

I had a similar issue and it was the fuel hose/primer bulb assembly. The primer bulb was collapsing under high demand.

 

[j_martin]

Re: Merc 150 bogs at 5000rpm

I had a similar issue and it was the fuel hose/primer bulb assembly. The primer bulb was collapsing under high demand.

Yep, that was one of them. I shot the bug with a pressure gauge in my lap, and every one of the listed items helped some. I guess Mr. Murphy was supervising the fuel system.

Oh, and on the list where I have "fuel hose barb" it was the actual bayonet fitting on the motor. An aftermarket plastic one had been put there by the certified merc mechanic. It was the last thing I fixed, and the improvement was significant. I don't even recommend a bayonet connector on anything over 135 horse in a carb motor. They just need so much fuel that you need to make the path as simple and free as you can.

John