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Stator/rectifier question 92 Mercury 50 hp 3 cyl.

A

arild_johannessen

Contributing Member
Hi
Just bought my self a 92 Mercury 50 hp (3 cyl) that not will pass approx. 2500 rpm.
Previous owner had it to a workshop,they took a compression test(all cyl. well),changed fuelpump,cdi-unit,
rebuildt the carbs,then the owner stopped them cause it started to be expencive.

Have set the ignition timing correct,so the engine runs really great at idle speed now.Fore some reason I dont now ,the workshop had put the timing way out.


I suspect stator faullt,understand that the stator on this engine has one low speed and one high speed winding,
is this correct?
Have measured the stator all way,every value is fine except between the two yellow wires that was connected to the
small type rectifier,value here(0.5 ohm) was 3 times more than the specifications chart says.
The stator has been replaced before I guess,partnumber is 174-9710 K
So I wonder,if using this 16 amp stator, I meen a voltage regulator/rectifier should be wired in somewhere,right?

This engine has just a small rectifier and output here is way to much(16-17 V) at idle speed.

Have not run the engine with load(out at sea) yet.


Could the wrong ignition settings cause this?
Do I need a new stator and/or a voltage/rectifier?

What should I do,anyone here that can help?

(Forgive me if the english is bad,am a Norwegian)
 
Timing is usually set for " maximum advance " at full throttle.-----Timing generally does not need to be changed for the life of the motor.--------How did you set the timing ?------Serious engine damage can result from wrong timing.
 
Your english is excellent.
I meen a voltage regulator/rectifier should be wired in somewhere,right? This engine has just a small rectifier and output here is way to much(16-17 V) at idle speed.
Click to expand...
One in the same. The regulator portion of the unit has quit functioning. Need to replace it. You are not using a maintenance free sealed battery are you?
 
To Racerone

Set the timing like this: 4 degrees ATDC at idle speed and 22 degrees BTDC at wide open throttle.
It was 10 out of settings on both.If it was the last owner or the workshop who did this I don`t now.

But can this be the cause to the rpm issue?
 
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guyjg said:
Your english is excellent. One in the same. The regulator portion of the unit has quit functioning. Need to replace it. You are not using a maintenance free sealed battery are you?
Click to expand...

Can i use the same type rectifier, doesn`t this small type just change the AC-volt into DC-Volt or does it regulate the Volt too?

On Ebay the seller has a important note about the 174-9710K stator that says: DO NOT USE WITH A RECTIFIER ONLY.
* ALL 16 AMP OR HIGHER STATORS REQUIRE AVOLTAGE REGULATOR.


Can this have something to do with the rpm issue,since I have just a rectifier,or is it something that is just bad fore my battery?

​
 
The rectifier has to do with charging the battery.--The small rectifiers just change AC to DC.-----------The ignition system is self powered and has nothing to do with 12 volts from the battery.---------The timing may have been the lack of power issue.----Time for a test run.
 
The only affect a nonregulated rectifier will have is a slightly higher spark voltage and a tendency to boil/overcharge the battery...will need to add distilled water more often. Install a rectifier/regulator from Mercury. Call Mercury (920) 929-5110 w/your boat serial number and ask them which rectifier/regulator to use.
 
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kimcrwbr1 said:
Another thing to look at is throttle opening and sync between ignition advance and throttle opening. Confirm the engine is in sync and the throttle butterfly is fully open at WOT. Also you didnt mention you checked for a proper spark gap. Get a spark gap tester and confirm it jumps a gap of at least 9/16 inch I believe for your ignition. Confirm you have the proper spark gap nice brite blue crisp snap?
Click to expand...

Have already done the carb and ignition sync, and checked the spark strenght,look good.
 
Did today: disconnected rectifier and tested it,its GONE

So,now that I need a new one,maybe i should go fore the combined regulator/rectifier?

What about the value between the two yellow wires:0,5 OHM ,Manual says slighty lower,
do you think the stator is ok or?
 
guyjg said:
Did you test the stator w/a digital volt/ohmmeter or analogue meter?
Click to expand...

Tested it with a digital one.

I guess I will disconnect the two yellow stator wires from the rectifier put the boat at sea,
and see if I still have the rpm problem,if working good ,well then I now that the rectifier has to be changed.

If rpm still is bad maybe a new stator has to be ordered too?
 
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Found this interesting information according to the 174-9710K stator by CDI-Electronics: High speed miss or weak hole shot:
1. Connect DVA meter to the blue and blue/white wires and do a running test. The voltage should show a smooth climb and stabilize,
gradually falling off at higher RPM's (above 3000). If you see a sudden drop in voltage right before the miss becomes apparent, the
stator is likely at fault. Repeat the test for the red and red/white wires. There should be a smooth climb in voltage with no drop at all
up to wide-open throttle.
2. Connect DVA meter to the red and red/white wires. The voltage should show a smooth climb throughout the RPM range, a sudden
drop or decline in voltage indicates a problem usually found in the stator, although a rectifier can cause the same symptom.
3. Disconnect rectifier/regulator and retest. If the problem disappears, replace the rectifier/regulator and retest.
4. For a high speed electrical miss, rotate the stator one mounting hole and retest. If the miss is still present, the stator may be bad.

So clearly the first thing to do is run the engine at sea with the two yellow stator-leads disconnected,if problem is gone, buy a new
voltage regulator/rectifier.
If the high speed rpm still is missing,a new stator and a new voltage/rectifier has to be bought.

Agree?
 
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kimcrwbr1 said:
Be sure and isolate the yellow wires good so they dont short to ground during the test
Click to expand...

I will.
May take some time before I can do this test,cause here in Norway it is still very cold(below zero),
so I guess I will wait some weeks .
I will reply in the thread when done.
Many thanks to you and all others fore the good words and knowledge.
 
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Have tested at sea today,with the two yellow stator wires disconnected,same problem.
Did a multimeter-test on the stator,do have full continuity between them,is this correct?
The resistance between them are 0,5 ( The specifications in the service manual says 0,16-0,19)

Any thougts about what to do now?
 
guyjg said:
use the troubleshooting guide http://www.cdielectronics.com/support/
Click to expand...

I will get my self a DVA meter or a DVA adaptor to my multimeter, and some piercing probes and do a DVA-test.

Just to be sure,do I set the meter to 1000Vdc or 1000Vac when doing the drop voltage test on the stator?
I thought the stator produced ac at the red and blue wire.

And should the two yellow wires stay disconnected from the rectifier, the CDI manual says nothing about this.

Sorry for asking so much, but I am a amateur in the beginning of understanding this electronic things, mecanic has been
mine tasks until now. Afraid of doing something wrong, and blowing things away.
 
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Have tested this weekend and all this values are done by cranking :

(Stator:174-9710K)
Stator Resistance: Low speed: 523 high speed: 27.9

Stator DVA-values(peak) are : 216V / 274V------------------------- 54V / 49V
---------------------Low speed: conn / disc ------------high speed: conn / disc

Trigger resistance : 1 2 3
1182------------ 1191--------- 1167



Trigger DVA-values(peak) are: 1 2 3
1.2V 13.5V-------------- 1.2V 13.1V------------ 1.3V 13.8V
conn / disc-------------- conn / disc ------------ conn / disc



Trigger values without the peak-reading: 1 2 3
2.0V 3.9V----------1.9V 2.2V---------- 2.2V 3.9V
conn / disc ------ conn / disc--------- conn / disc

Do I have a Trigger problem here or?

Just fore the rec:Engine runs smooth and idles nice,it just won`t pass appr.2800-3000 rpm.
New fuelpump
New Cdi-pack
Carbs rebuildt


I am not giving up yet,but I have to admit,I am getting some new grey hair trying to solve this problem.

Could this be a reed problem?

Suggestions?
 
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kimcrwbr1 said:
Oh yea running the engine in gear out of the water can also damage the prop if it doesnt have resistance at high speeds another thing to keep in mind.
Click to expand...

The dva testing were done by cranking in a tank, but trying to get full rpm at WOT were of course done at sea.
The boat are just 14 feet,and with my previous suzuki 30 hp it were real fast in plane and did 32 knots.

This Mercury was on a 17 feet boat , and ran well for years,until it suddenly would not give more than ca 3000 rpm,
so I guess its not a prop/boat problem

The engine runs really smoothly at idle.

The earlier owner has changed :Cdi-box,
New fuel pump
Rebuildt the carbs

I have tried the old cdi-box too, runs exactly the same.

Cuold it be a bad trigger that possible blows cdi-boxes,making a short circuit in trigger circuit?
Weak spark at all cyl?
 
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guyjg said:
Ohm the trigger to see if it's in specs.
Click to expand...

It is inside specs, slightly over 920 on all three.(my own multimeter)

The former DVA-test was done with a borrowed multimeter from work,but it was difficult to read it,was a little bit to advanced for me I guess, many different numbers to look into at the same time.

Have order a CDI DVA-adapter and a load resistor from the U.S, so I can do a full test on all the components,but it will proberly take at least a week until I have it here in Norway.


Tried to read the sparkplugs today after running a while at idle, and the bottom one seemed a little wet,not with water but unburned fuel.
Looking into to the cylinder with a light, I can see that some off the carbon-buildtup on just that nr 3 piston top has loosen.

Does this indicates something or?
 
I know you said the spark tested goodd, but did you pull the coils to inspect the bottom sides for damage and clean the grounds? If they are good the it's time to physically look at the stator and trigger to see if there are any cracks or buens or blisters in the inslulation.
 
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