150hp Mercury run great out of water dies when put in gear when in water

stophie11

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Jul 10, 2011
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Hey guys I have a 150hp merc that has carbs it starts and runs great out of the water on muffs but in the water it dies as soon as you put it in gear. Guessing it a carb problem...were do I start? Anybody got a PDF of the instructions or a schematic of the carbs, were is the fuel pump? What does the fast idel do it doesn't move the throttle on the carbs? I appreciate your help:confused:
 

daveswaves

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Mar 22, 2002
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Re: 150hp Mercury run great out of water dies when put in gear when in water

Your question is too vague to really help. We need to know what year Merc, inline 6 or V6, history of motor, did you just get it, did your buddy just tune it up in the driveway? you are likely just too lean on the carbs, but specific advice can be given for a specific engine.
 

stophie11

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Re: 150hp Mercury run great out of water dies when put in gear when in water

It's a v6 I bought it from a guy last winter who said the carbs had just been rebuilt and he spent alot of money getting that done. The carbs do show that someone had worked on them and done a nice job they look clean. I don't know the yr but I think somewhere around late 70's early 80's. The motor starts in the water and idels high with the high idel lever, but when lever is down the motor rpms is very low and teters on stalling when you put it in gear the prop will spin at idel speed but when you try to give it any gas it dies. With the cover off in the water in neutral if you manually operate the throttle body the motor bogs out. pls help
 

CharlieB

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Apr 10, 2007
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Re: 150hp Mercury run great out of water dies when put in gear when in water

Check spark on each cyl using an adjustable gap spark tester set to 7/16 inch.

One or two dead cyls will run fine out of the water, idle poorly in the water, and die the moment shifted into gear.

Repost your progress and we can proceed from there.
 

stophie11

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Re: 150hp Mercury run great out of water dies when put in gear when in water

Check spark on each cyl using an adjustable gap spark tester set to 7/16 inch.

One or two dead cyls will run fine out of the water, idle poorly in the water, and die the moment shifted into gear.

Repost your progress and we can proceed from there.


Ok had to buy a gap checker on internet will let you know what exactly am I looking for ?
 

stophie11

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Re: 150hp Mercury run great out of water dies when put in gear when in water

I took the boat to a marine mechanic and he replaced the stator and switch box on rt side on the motor, the motor ran better in the water, but not great had trouble getting out of the hole but once planed up ran better like when the carbs were not leaning backward the motor ran bad once we trimmed the motor foward it ran better the mechanic said it was probably the reeds and told me by the time I sank the money into it to fix it right I would have to much money in it, so being the very fair guy he is he is going to put my old parts back on and let me take my pos back...so I have v6 merc 150 hp that needs a new stator switch box and carb work reeds and such....think I could fix this myself ???? I hear there is a mercury special tool to take the fly wheel off, how hard is it to do the carbs and were is the best place to get the parts?
 

Chris1956

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Mar 25, 2004
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27,036
Re: 150hp Mercury run great out of water dies when put in gear when in water

First of all reed valves rarely go bad. Since your mechanic suggested this, either he is a bad mechanic, or he inspected them. First take a compression test and report results.

if the compression is good, test for spark on all cylinders. let us know which cylinders do not spark, as they point to trigger, stator or switchbox.
 

starkyb

Petty Officer 1st Class
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Apr 21, 2007
Messages
217
Re: 150hp Mercury run great out of water dies when put in gear when in water

I had problems with my outboard and it turns out that there was water in my tank from condensation. I checked just about everything from the plugs, I rebuilt all three carbs and decarbed the motor. After my mechanic worked on it he finally hooked up my motor to his gas tank an it ran perfectly. My solution was to fill the tank all the way put in a bottle of Heet and 4 ounces of Mercury Quicklean. Now my motor runs like new. I'm not saying this is your problem but it is a place to start without having somebody look at it.
 

j_martin

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Sep 22, 2006
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7,474
Re: 150hp Mercury run great out of water dies when put in gear when in water

There's 2 ways to go about getting the engine to run right.
1. Take all the anecdotal advice from friends and "mechanics" which usually says to replace the most expensive parts without testing anything, sometimes repeatedly.

2. Get the Manufacturers srvice manual, start at the beginning with systematic diagnostics and repair the problems as they are found.

When I bought my XR4, it had a problem at WOT. I knew it, and I got $500 off on the price for owning the problem. Altogether there were about a dozen things wrong, from dirty fuel tank to many adjustments and wrong parts installed by a "certified mercury mechanic".

For about $200 in parts and a couple of weeks of learning and doing, I had one more problem.
I then had to buy a steeper prop because the engine was strong enough to over-rev with the prop that was on it. Gained about 10 mph in top speed just fixing it. Original Owner had no idea that he owned such a fine machine. I didn't modify the engine, just put it in proper tune.

Systematic diagnosis is the fastest and least expensive path to complete repair.

That's usually true even if you have to buy tools to get the job done. Bonus is you then own the tools for next time, or to help others.
 
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