84 Merc 200HP - Won't Accelerate Past 3400RPM

wcsd106

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First off, I'm still looking for a service manual for my motor. I think I have found it here: Link

Until I can get the manual, I'm still trying to troubleshoot engine problems.

Before, I was having prop shaft issues. That has been replaced and the service tech replaced the fuel pump diaphragm at the same time since one of the cylinders was flooding out when he tried to fire it up to test the engine.

I was finally able to get back onto the lake today and was met with disappointment.

Idling seemed fine and the engine fired right up. After idling out of the no wake zone, I went to throttle up the motor. It seemed like it was bogging down and just didn't want to push the boat up out of the water and onto plane.

The tach showed a max RPM of around 3400 at WOT. Well below the 5K+ that I should be seeing.

The prop in use was recently rehubbed and was the prop that has been on this engine for years including which time it was in good operating condition.

After I got home, I started looking over the engine to see if I could find anything obvious sticking out.

The one thing I noticed was that the fuel input fitting running to the top carb from the fuel pump was loose and would turn by hand. I removed the fuel line running from carb to fuel pump and tightened the fitting then replaced the fuel line. Before it was tightened, I hit the primer bulb and fuel was leaking around the threads.

All of the spark plugs look decent.. not shiny or brand new, but not destroyed and burnt up. They are cheap enough that if necessary I may replace those as part of a standard tune up as I get this thing up and running.

I am still at a loss as to why the engine sees around 3400RPM at WOT. I have limited experience with marine engines, but my first guess would be carbs or ignition.

Is there a good place to start checking that I could do before I get my manual?

Also: Is the manual I linked above correct for my motor? 1984 Mercury Black Max 200HP V6?

--->

I have been searching through the forums and reading some notes over at CDI electronics. This appears to be an ignition related problem. Any suggestions on getting started with this?
 

BassnKY

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Re: 84 Merc 200HP - Won't Accelerate Past 3400RPM

It looks to be the correct model. To be sure of the year, I would use the link in the thread at the top of this section. I do know that with Mercury, you have to look up item by S/N.

As for the lack of power, you might have found the problem. If it was sucking air it might not get the fuel it needs. Have you tried it since tightening the fitting?
 

wcsd106

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Re: 84 Merc 200HP - Won't Accelerate Past 3400RPM

Thanks for the reply.

I haven't tested it since tightening the fitting, though I don't believe that it is the sole problem here.

The fuel pump was replaced last week during a prop shaft repair, but the first time I took the boat out this season I was unable to get the boat over 3400 RPM either. Not sure whether or not the fitting was loose at that time or not.

I have a set of flushing muffs, but I've always been told that you don't want to rev an engine very high unless you're actually in the water putting a load on the prop. Might fire it up tomorrow afternoon just to see how it runs on city water though.
 

BassnKY

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Re: 84 Merc 200HP - Won't Accelerate Past 3400RPM

Correct!!! Do not rev up a motor, even in gear, without some resistance on the prop. It's kind of like revving a car in neutral. It could over rev and fly apart (sometime literally) I saw a car over rev at a stock car race when the driver had a heart attack. Parts were flying through the hood. It is a site I will never forget!!! :eek:
As far as the fitting goes, that could cause the problem. When the pump was demanding a lot of fuel it could have been getting air instead of fuel as air is easier to pull in through the leak than fuel through the long fuel line. I would be the same as if the pump was bad and couldn't draw enough fuel.

I would test it out before going further. Sometimes is is something simple.
 

BullyARed

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Re: 84 Merc 200HP - Won't Accelerate Past 3400RPM

Have you replaced your fuel filter? This is perhaps the simplest thing but often overlooked! I did! I replaced mine and it works. At first I thought it was the fuel pump but before going to do drastic work, I inspected the fuel filter and it was the problem (see my thread on 2000 Mercury 200HP hesitates on acceleartion.) Good luck.
 

wcsd106

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Re: 84 Merc 200HP - Won't Accelerate Past 3400RPM

Fuel filter has been replaced. If I have time this week I'll give it an on the water test. Hoping that's all it was.
 

BassnKY

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Re: 84 Merc 200HP - Won't Accelerate Past 3400RPM

GOOD LUCK!!!

Let is know how it goes.
 

BullyARed

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Re: 84 Merc 200HP - Won't Accelerate Past 3400RPM

BTW, check the fuel primer also. If it is soft, replace it.
 

wcsd106

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Re: 84 Merc 200HP - Won't Accelerate Past 3400RPM

Primer bulb and fuel lines from tank to filter to engine have been replaced also.

A little history on this engine:

This was my Grandpa's bass boat. I spent pretty much all of my youth fishing with him in this boat. After he passed a few years ago, I got this boat. He had been in poor health and was unable to use the boat for many years, so it had sat dry for somewhere in the neighborhood of 8 years or so before I started getting it ready for the water.

As part of my prep for the water, I checked and replaced the fuel lines, water separating fuel filter, primer bulb, and water pump. The fuel pump diaphragm was replaced last week by the local marine mechanic when he was testing the prop shaft repairs.
 

BullyARed

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Re: 84 Merc 200HP - Won't Accelerate Past 3400RPM

You may need to clean all the carburators. The high speed jet could be clogged up. Good luck. Try to test with the new fuel filter first.
 

Mi duckdown

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2,575
Re: 84 Merc 200HP - Won't Accelerate Past 3400RPM

If was Me. I would buy an OEM Merc manual for that year, HP Need serial number. Pricey but worth every penny. 85.00 bucks. And yes clean the carbs. Maybe some seafoam run thru system might help.
Did you do compresion check on the cylinders and spark plug check also.
it comes down to the basics.
not trying to dumb you down.
the oem manual will tell you everything. NOT SELOC/CLYMERS. Junk
 

wcsd106

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Re: 84 Merc 200HP - Won't Accelerate Past 3400RPM

Thanks for the reply. Do you know where I could purchase an OEM Manual for that motor? I have the serial number. Just having trouble finding the manual.
 

BassnKY

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Re: 84 Merc 200HP - Won't Accelerate Past 3400RPM

I am not sure. I have tried to search the net but have had no luck. Mine is a Seloc
 

wcsd106

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Re: 84 Merc 200HP - Won't Accelerate Past 3400RPM

I ordered a seloc last night through Iboats. It came with a one year subscription to the seloc online. I can say that I've been pretty impressed with it.

Everything I've read/found said that unless you're a dealer you're not going to get the OEM Manual. I guess Mercury holds onto them pretty tightly. I hope I've been misinformed.
 

wcsd106

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Re: 84 Merc 200HP - Won't Accelerate Past 3400RPM

I may have possibly found all/part of the problem this evening. I will be posting several pictures shortly once I set up a photobucket account to host them.

I was discussing my problem with a coworker today who used to work at one of the local boat factories. He told me that he had run into a similar problem with a mercury outboard of around the same year / model. He told me to really inspect the wiring harness in and around the switch boxes and coils.

To make a long story short, I inspected wiring this evening and found several wires that the insulation had cracked away from and the wiring was severely corroded. One of the wires even broke when I touched it lightly.

Whether it fixes the problem or not, I know these wires will need to be replaced. Here is a list of the wires that I know are broken at this time:

2 Broken Yellow Wires - Connected to Rectifier
1 Red wire Broken at Both Ends - Runs to Idle Control Module

There is also one Violet wire with a quick disconnect on it that is unhooked in the wiring harness. As I said, pics will be posted very soon.
 

wcsd106

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Re: 84 Merc 200HP - Won't Accelerate Past 3400RPM

015.jpg


Broken Red Wiring to Idle Control Module


008.jpg

Frayed Insulation Around What I believe is a Ground

009.jpg

Other End of Wire Above - Also showing Cracked Insulation


006.jpg

Unidentified Purple Wire
 

wcsd106

Petty Officer 2nd Class
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Re: 84 Merc 200HP - Won't Accelerate Past 3400RPM

005.jpg

Other End of Idle Control Module Wiring - Broken Insulation & Corroded Wire

004.jpg

Rectifier Wiring - Cracked Insulation, Corroded Wiring

003.jpg

Rectifier Wiring - Closeup

007.jpg

Additional View of Unidentified Violet Wire



So I know full well that these wires are going to have to be replaced. I have read that the idle control module is not necessary, but I can't see Mercury spending money on unneeded parts on a motor when the bottom line of business is to maximize profit.
 

CharlieB

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5,617
Re: 84 Merc 200HP - Won't Accelerate Past 3400RPM

Disconnect the idle control module and THROW IT AWAY. They are NOT really necessary and have proven to be the source of MANY running problems when they begin to go bad.

CDIElectronics.com wrote the book on troubleshooting outboard ignitions, and have made it available for FREE download, check out their site.

Running a V6 on the hose even with a dead cyl, may still sounds good, you cannot know for sure til it is in the water again.

Check spark on all cyls using an adjustable gap spark tester set to a 7/16 inch gap, if any fail to provide a hot blue CRACKLE, then follow the steps outlined in CDI's guide to isolate the problem.
 

wcsd106

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Messages
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Re: 84 Merc 200HP - Won't Accelerate Past 3400RPM

Disconnect the idle control module and THROW IT AWAY. They are NOT really necessary and have proven to be the source of MANY running problems when they begin to go bad.

CDIElectronics.com wrote the book on troubleshooting outboard ignitions, and have made it available for FREE download, check out their site.

Running a V6 on the hose even with a dead cyl, may still sounds good, you cannot know for sure til it is in the water again.

Check spark on all cyls using an adjustable gap spark tester set to a 7/16 inch gap, if any fail to provide a hot blue CRACKLE, then follow the steps outlined in CDI's guide to isolate the problem.

Thanks for the advice.. Here is a quote from the CDI PDF File on Merc v6 engines from my model year.

WILL NOT ACCELERATE BEYOND 3000-4000 RPM:
1. Disconnect the Yellow wires from the stator to the rectifier and retest. If the engine now has good spark, replace the
rectifier.
2. Disconnect the idle stabilizer (advance module) and reset the timing between 23-25 degrees Wide Open Throttle. If the
problem clears, discard the idle stabilizer as it is not needed.

I'm thinking that I may be onto my problem.
 

CharlieB

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Re: 84 Merc 200HP - Won't Accelerate Past 3400RPM

That is correct.

Eventually you will want to replace that stator, but for now, you can remove it, clean all the cracked brittle insulation off, and re-coat the exposed wires with liquid tape. It is available in colors. Multiple coats will successfully re-insulate each wire and you can continue to run that stator until an inner winding goes bad.

I've used this method successfully on obsolete ignition coils to restore very old motors.
 
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