92 Mercury 50 HP will not accellerate

[Iceman66]

Bought myself this engine some weeks ago, and the problem is that the engine suddenly would not accellerate beyond appr.3000 rpm.
It idles smooth,but runs a little bit weak maybe?

Previous owner had it to workshop, they changed fuel-pump,power-pack and rebuildt the carbs,no difference.
He would not spend more money on it, so I bought it,thinking that this problem could be solved, but now I am really
starting to wonder.

I have now done all the DVA-testing like the CDI-troubleshooting says ,using the CDI DVA-adapter,and it seems that
all values are inside spesifications.

Here are the values (cranking): STATOR DVA: low speed 245V(connected) 274V(disconnected)
high speed 52V(connected) 46V(disconnected)


Stator resistance: lowspeed-521 ohm highspeed-27,6 ohm


Trigger DVA : 8,5V connected and 12V disconnected on all 3 cyl. Resistance on all are about 1175 ohm

Powerpack DVA to the coils are about 240V at idle.

Have done carb and ignition sync, set the timing correctly,compression is 112psi-115psi-119psi (1 2 3)

I am lost here,anyone with some good advice here,will be much,much appreciated.
Have tried with the 2 yellow stator wires disconnected,no difference.

 

[Laddies]

Re: 92 Mercury 50 HP will not accellerate

Don't worry about the OHM reading, you need to get a reading on the high speed winding at speed to see if t is failing.

 

[sib240]

Re: 92 Mercury 50 HP will not accellerate

i had a 90s 20hp mariner that had the same problem i tryed many things in the end i changed the plugs and it flew so try the plugs if not already done so.

 

[Iceman66]

Re: 92 Mercury 50 HP will not accellerate

i had a 90s 20hp mariner that had the same problem i tryed many things in the end i changed the plugs and it flew so try the plugs if not already done so.

Have tried with new BU8H and BP8H-N-10 , still the same.

 

[CharlieB]

Re: 92 Mercury 50 HP will not accellerate

.......................
Here are the values (cranking): STATOR DVA: low speed 245V(connected) 274V(disconnected)
high speed 52V(connected) 46V(disconnected)

....................

Like Laddies says, need to test the high side of the stator running.

The high speed windings voltage output starts low and increases with RPM, by 2500 it should be near 240 , if not then you may have found your problem.

Just remember, there is NO RETURN on electrical parts, test, re-test, then test it again, PROVE the fault before spending your hard earned cash.

 

[Iceman66]

Re: 92 Mercury 50 HP will not accellerate

I will try out at sea this weekend if weather is good.

I really,really hope the dva-reading shows something wrong.

 

[Faztbullet]

Re: 92 Mercury 50 HP will not accellerate

Stator resistance: lowspeed-521 ohm highspeed-27,6 ohm

Somethings not kosher with this...............
Check resistance from the blue to the blue/white stator wire. OEM will read approximately 3500 ohms Check resistance from red to red/white. It should be approximately 80 on OEM stators

 

[Iceman66]

Re: 92 Mercury 50 HP will not accellerate

Somethings not kosher with this...............
Check resistance from the blue to the blue/white stator wire. OEM will read approximately 3500 ohms Check resistance from red to red/white. It should be approximately 80 on OEM stators

I do not have OEM-stator, but the 174-9710 from CDI, so stator has been replaced once before.
On three cyl. engines are blue/white and red/white connected to ground and ohm-values different.

One thing I`ve not tried, is to disconnect all the wires from rectifier(small type) ,just the two yellows from stator.

Could the be a interference between the rectifier(if defect) and ignition parts although the yellow wires are disconnected, since they have the same engine ground base?

 

[Iceman66]

Re: 92 Mercury 50 HP will not accellerate

Started the engine(in tank) again today, and it was really hard to start.
Engine ran smooth but kind of weak at idle,and in a period of a minute it ran slower and slower and finally died.

Checked the plugs,were wet(unburned fuel)

Could I have a fuel or a combustion problem after all?

 

[CharlieB]

Re: 92 Mercury 50 HP will not accellerate

Flooded, fouled plugs, no spark, you really have no idea until you start testing.

 

[Iceman66]

Re: 92 Mercury 50 HP will not accellerate

Flooded, fouled plugs, no spark, you really have no idea until you start testing.

Ok
Will take the boat out at sea as soon as possible, and do the high speed winding test,will reply when done.

 

[Faztbullet]

Re: 92 Mercury 50 HP will not accellerate

One thing I`ve not tried, is to disconnect all the wires from rectifier(small type) ,just the two yellows from stator.

Could the be a interference between the rectifier(if defect) and ignition parts although the yellow wires are disconnected, since they have the same engine ground base?

You may have found your problem...CC below from install sheet.
"Note: 174-9710K1 requires a voltage regulator, DO NOT USE WITH A RECTIFIER ONLY."
www.cdielectronics.com/Portals/0/installsheet/174-9710K1.pdf

 

[Iceman66]

Re: 92 Mercury 50 HP will not accellerate

You may have found your problem...CC below from install sheet.
"Note: 174-9710K1 requires a voltage regulator, DO NOT USE WITH A RECTIFIER ONLY."
www.cdielectronics.com/Portals/0/installsheet/174-9710K1.pdf

Have tried at sea today and dva-output is fine on blue and red stator wires.

I know about the cdi-stator and voltage regulator issue, but I thougt since I disconnected the yellow charge coil wires from the
small type rectifier , I just exluded the charging part of the stator.

Is this wrong or does all these influence on each other?

 

[Iceman66]

Re: 92 Mercury 50 HP will not accellerate

I noticed one thing today,when idling its almost that I can here sparking some place outside the block,but I can not see
any .
Could the be a short under the flywheel ,in the trigger or stator?

Have done dva-output on the trigger (idling),its inside values, but I thought when I read between the three different
wires and engine ground the output was high.Repair manual says 1V+, I had 11V on all,isn`t that to much?

 

[CharlieB]

Re: 92 Mercury 50 HP will not accellerate

Trigger voltage rises from 1.5 to @ 3 at speed, you may not have your meter on the correct range. Trigger voltage simply tells the switchbox to send the stored stator voltage to the coil.

You may have indeed heard arcing.

Any coil or plug wire arcing to ground will seriously reduce power as that cyl would not be firing.

Remove and inspect all ignition coils for any carbon arcing, a small burnt spot that could be a short to ground when voltage gets high enough.

Also check plug wires carefully for same.

You could try running the motor at night to see if any arcing occurs.

 

[Iceman66]

Re: 92 Mercury 50 HP will not accellerate

Trigger voltage rises from 1.5 to @ 3 at speed, you may not have your meter on the correct range. Trigger voltage simply tells the switchbox to send the stored stator voltage to the coil.

You may have indeed heard arcing.

Any coil or plug wire arcing to ground will seriously reduce power as that cyl would not be firing.

Remove and inspect all ignition coils for any carbon arcing, a small burnt spot that could be a short to ground when voltage gets high enough.

Also check plug wires carefully for same.

You could try running the motor at night to see if any arcing occurs.

My meter makes the range automaticly, but I will do the test once more.

I will check the coils and plug wires,
also have another older 45mercury with same type of coils and can try them.

Will reply when done.

 

[Iceman66]

Re: 92 Mercury 50 HP will not accellerate

Think I`ve got it.
Have done all the CDI-troubleshooting test several times,all values looks good.

I am pretty sure that I have a water leak at least in my bottom cylinder,can see water droplets inside with a good light, and top of bottom piston has loosen mostly of its normally carbon buildtup.

When running slightly over idling,it periodical comes an amount with white smoke out the exhaus.

Time for taking the powerhead off and tear it apart I guess.

The big issue: where is the leak,this block does not have any exhaus-coverplate or a headgasket,its all made in one.

Crack in the block, lower crankshaft seal, exhaustplate?

Guess I will see when I tear it apart, but anyone know what the usual place for a water leak is?

 

[CharlieB]

Re: 92 Mercury 50 HP will not accellerate

Most common is a gasket leak on the exhaust plate, or a crack in the inner exhaust plate, either will allow cooling water to spray into an exhaust port.

Very careful removing exhaust plate bolts, they have a nasty habit of seizing and breaking off.

 

[Iceman66]

Re: 92 Mercury 50 HP will not accellerate

Most common is a gasket leak on the exhaust plate, or a crack in the inner exhaust plate, either will allow cooling water to spray into an exhaust port.

Very careful removing exhaust plate bolts, they have a nasty habit of seizing and breaking off.

Will start the disassembly later today.

Do you think I am on track to my problem here?
I really hope so.

 

[Iceman66]

Re: 92 Mercury 50 HP will not accellerate

Found the problem for sure!!
Some amateures has clearly done some work inside the block!!!
The cylinder sleeves has been changed at some time,and two of them are not pressed into the bottom,or the work
has been poorly done so they have work themself upwards in the cylinder, they have even tried to secure the sleeves
by weld a BIG aluminium perl on the block near the sleeve edge.
Thats not all,two off the pistons also were a tiny bit seized at one side, and one of the rings were bad, cylinders could get well by honing I think.

So my question is: Is it possible to try and press the sleeves down to its place in a hydraulic bench,how is this usually done?

What I really think is : Should I even try fix this engine ,maybe better to get a new/used ok powerhead.

Suggestions?