1988 Force 1251H8C overheating

[21BaylinerCC]

I have a 1988 125hp force outboard that keeps over heating when I throttle up to around 3000 RPM.
I've checked compression... Cylinders 1-4. 140psi, 138 psi, 138psi, 138 psi, respectively.
I've checked the external temperature of the water jacket/cylinder head (127 degrees F), Thermoswitch (102 degress F), Exhaust plate (101 degrees F), and thermostat cover (105 degrees F), after the overheat buzzer sounds.
I replaced the thermostat and the thermoswitch. I flushed water up the intake tube and down through the thermostat housing - water flowed steadily. I also replaced the impeller - the previous impeller looked fine, but wanted to rule it out.
I also cleaned the carburetors and set the floats according to the US Marine shop manual.
I've done a link and sync, checked and set timing to the correct specifications based on the manual.

I notice cylinders 1 and 3 look to be wet fouled, which leads me to believe it could be the trigger (its the only commonality between cylinders 1 and 3, as they are triggered by the same colored wires from the trigger).
I am also contemplating removing and cleaning the fuel re-circulation system.

Anybody have any ideas?

 

[jerryjerry05]

Trigger and recirc system have nothing to do with overheating.

If the temps are what you say they are it shouldn't be overheating.
The thermo should be a 130d and all the temps are under that.

The new thermo switch, used? or new?
If the buzzers going off and it's not hot? then I'd say maybe the switch is the wrong one or it's defective??

What condition is the pump housing and the wear plate under the impeller?
The housing can be in bad shape and still work.

How you measuring the temps?

I bought a heat gun on eBay about 16$
One of the better purchases I made.

Run the motor and take the temps as you run.
Paying particular attention to the area around the sending unit.

When you removed the thermo, how much crud was on it?

 

[21BaylinerCC]

Thermoswitch is brand new.
The reason I replaced the parts in the first place, is overheating. So I had the same overheating problem with the old parts. The old thermostat looked decent, not remotely near the condition of the one in the pic you sent.
The pump housing looks good - not much wear on the plate. I did replace the housing and plate a couple years ago, and i replace the impeller every 1-2 years, depending on if i make it out a lot during the fishing season.

I measured the temps with a temp gun (like you mention).

The reason i suspect the trigger, is because of wet fouling - my thinking is the trigger is defective, causing the cylinders not to fire properly. If the trigger is defective, then theoretically the trigger module would not release the CD capacitor voltage to the coil at the correct time (or ever), causing erratic firing, without being able to burn the fuel/oil mixture properly. I must admit, the engine does not seem to be misfiring, however (unless its possible it could be misfiring at the slightest without me being able to tell). Does this sound correct?

I've read some threads that with today's ethanol blended fuel, adjustment the timing past the manual specs can compensate for the use of ethanol fuel. Not sure i feel great about doing that, as that would start messing with the synchronization of the engine...

 

[The Force power]

Thermoswitch is brand new.
The reason I replaced the parts in the first place, is overheating. So I had the same overheating problem with the old parts. The old thermostat looked decent, not remotely near the condition of the one in the pic you sent.
The pump housing looks good - not much wear on the plate. I did replace the housing and plate a couple years ago, and i replace the impeller every 1-2 years, depending on if i make it out a lot during the fishing season.

I measured the temps with a temp gun (like you mention).

The reason i suspect the trigger, is because of wet fouling - my thinking is the trigger is defective, causing the cylinders not to fire properly. If the trigger is defective, then theoretically the trigger module would not release the CD capacitor voltage to the coil at the correct time (or ever), causing erratic firing, without being able to burn the fuel/oil mixture properly. I must admit, the engine does not seem to be misfiring, however (unless its possible it could be misfiring at the slightest without me being able to tell). Does this sound correct?

I've read some threads that with today's ethanol blended fuel, adjustment the timing past the manual specs can compensate for the use of ethanol fuel. Not sure i feel great about doing that, as that would start messing with the synchronization of the engine...

Here's a link that will guide you through the trouble shooting, look for your particular motor.
http://www.cdielectronics.com/wp-content/uploads/2013/02/CDI Troubleshooting Guide - 2012.pdf

IF.. your timing is set correct...don't mess with it!

Like jerryjerry already said; Trigger and recirc system have nothing to do with overheating !

Bench-test the the thermo-switch to see at what temp. its closes, also check the wire past the terminal-block for shorting to ground

 

[jerryjerry05]

Running premium? What type battery, deep cycle or regular?

 

[The Force power]

I have a 1988 125hp force outboard

I notice cylinders 1 and 3 look to be wet fouled, which leads me to believe it could be the trigger (its the only commonality between cylinders 1 and 3, as they are triggered by the same colored wires from the trigger).
Anybody have any ideas?

Yours would have the Presolite ignition system and the #1 / #3 do not share or have the same trigger colored wires.
(see the attached schematic)

 

[The Force power]

this one maybe more helpful;

 

[21BaylinerCC]

Jerry Jerry - Running regular with fuel stabilizer and synthetic TCW3 oil. Unfortunately, we have no ethanol free fuel where i am. I have deep cycle batteries, actually maintenance free (before i knew better with these "voltage un-regulated" engines). I removed the rectifier and installed a universal voltage regulator/rectifier, based on info i read on another post here about voltage spikes and force engines.

May the force be with you - Thanks for the schematics! I have both a clymer manual and the original factory Force manual (includes my C model), both which show the last schematic you posted. It shows cylinder 1 and 3 as having both orange and green wires... Regardless of the same color, they are not actually connected within the epoxy of the trigger, correct?

Before i removed the original rectifier, my tachometer would jump sporadically. I also noticed my engine was set to idle at around 1700 RPM (like that when i bought it). Before i performed a link and sync, the engine would overheat a few times throughout the season... forward idle or WOT, didn't matter.
After performing the link and sync, i cant get it to 3000 RPM and above for more than about a minute... I've been dealing with this all summer.
I am stubborn, and want to fix it, especially since it has good compression.
Any ideas?

 

[The Force power]

Jerry Jerry - Running regular with fuel stabilizer and synthetic TCW3 oil. Unfortunately, we have no ethanol free fuel where i am. I have deep cycle batteries, actually maintenance free (before i knew better with these "voltage un-regulated" engines). I removed the rectifier and installed a universal voltage regulator/rectifier, based on info i read on another post here about voltage spikes and force engines.

May the force be with you - Thanks for the schematics! I have both a clymer manual and the original factory Force manual (includes my C model), both which show the last schematic you posted. It shows cylinder 1 and 3 as having both orange and green wires... Regardless of the same color, they are not actually connected within the epoxy of the trigger, correct?

Before i removed the original rectifier, my tachometer would jump sporadically. I also noticed my engine was set to idle at around 1700 RPM (like that when i bought it). Before i performed a link and sync, the engine would overheat a few times throughout the season... forward idle or WOT, didn't matter.
After performing the link and sync, i cant get it to 3000 RPM and above for more than about a minute... I've been dealing with this all summer.
I am stubborn, and want to fix it, especially since it has good compression.
Any ideas?

The temps. you were mentioning are not alarming at all. what makes you convinced it's overheating? the buzzer only?
Disconnect the temp.sensor(that's what forms the ground-path for the already energized buzzer-circuit)

Run the unit like you have before and see if the buzzer goes, if it does; the wire AFTER the buzzer is grounding somewhere before its connected to the temp-sensor.

That particular schematic shows similarities in color, but the Trigger wiring for # is going to #2 switch-box that cause #3 to fire.
below is the schematic

 

[The Force power]

found a very interesting post that maybe helpful
type in the search-box; Water Bypass Valve - were does the water go?

I don't know if your block has the water bypass-valve
Apparently........your timing can affect your temperature, who knew??

 

[jerryjerry05]

"I don't know if your block has the water bypass-valve​

Apparently........your timing can affect your temperature, who knew?? "

His model​

1251H8C​

doesn't have the bypass installed.
The early 88's had it and then they stopped using it mid year.
It usually cloogged (real quick in salt water)up and the plug froze in the closed position.
When it was operational? the excess water went out the holes on the back of the mid section.

The deep cycle batteries might be causing a problem with your electrical system.??​

 

[21BaylinerCC]

Correct. No bypass valve. I'll try running it without the temp sensor hooked up - good point about it possibly grounding out.

JerryJerry - do you mean i should try using starter batteries instead of deep cycle batteries, or use conventional, non sealed batteries? I am thinking about removing the voltage regulator/rectifier and placing the rectifier from an '89 125hp force i have on it.

I've noticed that testing a lot of the electrical complements requires the engine to be running, sometimes at 4000 RPM to get an accurate reading (as, say, the charging system increases output as the engine revs up). Is this the only way to test the components? I've read that ohm readings tell you very little with, say, the charging system and trigger.

 

[jerryjerry05]

The deep cycle batteries can hurt the charging system.
They recommend not using them and use only as a last resort.
You should have a starting battery of at least 450 cca.
If you have a lot of electronics(radios,woofers, etc) get a bigger battery.
I had a set up of 2
One was a 1000cca and the other, any thing I could get
The boat came with one 450cca and I never killed it while fishing.

Test the wiring system.
Check to see if the harness has a short in the lead from the alarm system.

Some outboards need to be above 2000 rpm's to activate the charging system.
Once above the 2k they produce power at the lower rpm's.
Try a regular starting battery, sealed or not shouldn't make a lot of difference.

The batteries sold these days seem to have a built in timer that goes off at about
2 1/2 years old, then it dies and you need a replacement.
AHHH the Good Old Days!! When you could get 7-8 years out of a battery.

About the only way the OHM meter seems to do any good is when testing the stator.
And even then a stator that tests good, can be bad

Yes try the new reg after the battery's changed?

 

[The Force power]

With an unregulated charging system; it is not advised to use "maintenance free" batteries either, as the water boils-off and they can not (usually) topped up

Maintenance free = not serviceable :blue:

 

[Redbarron%%]

I have used a regulated rectifier from a Ducati Motorcycle on my Force / Mercury Sport Jet and it works well as far as the battery is concerned,
Since the coils are not regulated with a field signal they output full current all of the time and the voltage is really doen by the load on the circuit (as near as I can tell).
The MOSFET regulators seem to increase the current to increase the drop in the coils. I noticed that the heat in higher when used with the 16 amp red coils.
I have noticed a difference in running with the MOSFET regulator v the stock one, but I have not had a chance to run it with a lot of attention to the heat with my maintenance free battery.
I hope to soon get a chance to document the issues with the MOSFET vs the original regulator.
My concern is not the heating of the MOSFET regulator as it is rated to 60 amps, but rather the charging circuit coils.
I assume either way the coils will have a current that either drops their voltage to the correct amount with the standard battery or drives the system into over voltage condition with less current.