1996 Mercury 15 hp 2 stroke, wet lower plug

[AKDan]

Hi, I have a 1996 15 hp mercury 2 stroke that starts well only with new lower plug.
Compression has been checked. Upper plug is dry and light tan on insulator.

Just changed:
Remote tank, Fuel hose, Fuel filter assembly, and new correct plugs

If I put new Plugs (correct according to manual) It starts 2nd pull.
Rans rough at idle low speed setting. Sounds out of balance at low idle setting even with new plugs. Offers to die unless idle in fast.
There is a ping/mecanical sound in early throttle increase in rpm's. I wear hearing aids so may not hear as you do

Smothes out at speed and runs well at full throttle. Difficult to restart. Lower plug is wet and there is evidence it is firing. black liquid on plug


Previously:
A year ago had hard starting problems and apparent overheating per merc tech. Mechanic did tune up and removed thermostat as In his opinion in our low temperatures said didn't need it. Said carb ok after "power tune" sprayed in motor. Compression Checked out ok. He could not get engine to idle at lower idle speed.

Have bad back restarting is tough.

Thanks for any help you can offer!

 

[flyingscott]

What was done to the carb as powertune is not for the carb.

 

[AKDan]

Thanks for your comment.
I misunderstood the effect of power tune.
Note with new plugs with full choke motor has a 1 pull start.

Have continued trouble shooting and after doing a run at full throttle shut it down. Idea was to check the spark plugs for indicators that might help. Lower plug wet fouling changed when I shut down after full throttle run. Now lower plug has soft carbon all over it . Upper plug shows heat changes on ground electrode like lite scaling dulling going almost down to threads. After run, upper plug is very clean with little change on electrode insulator.
Book said carbon build up may be due to thermostat issues so put in thermostat. (Dealer Mechanic had removed it.) This time ;left motor on boat and ran in lake at full throttle for 25 minutes. water temperature in lake about 45 F. outside air temperature 39 F. Result on new plugs was the same on upper and lower.
Due to the disparity in results from upper to lower plugs I don't know what to look at now. Book says carburetor adjustment for rich condition might be needed for lower plug but upper plug seems either ok or lean..
Thanks for looking
AKDan

 

[flyingscott]

The thermostat is absolutely needed for that motor. Is the plug wet with fuel or water? If fuel look I would look into rebuilding the carb with a complete carb kit, this will include the primer and fuel pump diaphragms. If it is water look at the exhaust gaskets on the side of the motor.

 

[ondarvr]

What was done to the carb as powertune is not for the carb.

I don't think you answered his question.


​The carb would be one of the first things to check (clean), then make sure the bottom plug is firing all the time.

Also, what were the actual numbers on the compression.

 

[AKDan]

Thanks to all for your comments.

Original wet plug may have been because I ran the engine till fuel gone after disconnecting fuel line. Thinking at that time I would put it up for winter and deal with it in the spring. Since then I find there is a late Silver salmon run up a remote creek worth trying out.
My motivation to solve the problem increased a bunch. It will be low 30 degrees so don't want any problems downstream from launch.

Changed the plugs and after that run (still no thermostat) lower plug dry with carbon on it.

Installed thermostat when it came in.

After I installed the thermostat and ran motor at full rpm for 25 minutes the lower plug was dry and coated with carbon. ran a little rough at first and perhaps rpm's varied some for first 15 minutes. Toward the end of time the rpms were more consistent and, I felt, engine ran some smoother.

I don't know how to check for consistent firing to the cylinders while running. A rough test showed similar spark from spark plug to the head.

Thanks again to all

Thinking of trying for Deep Creek miracle on the bottom cylinder.

 

[flyingscott]

There is no miracle in a can to fix any motor.

 

[AKDan]

Thanks again

Trying to find my invoice. Mechanic didn't seem concerned whatever it was. " This motor will run for a long time" was what he said. Of course that would be true as long as I kept feeding it gas and didn't turn it off.
Its hard to restart

Any ideas on who to check spark while running?

AKDan

 

[racerone]

A repeated fouled plug indicates to me that the cylinder is not producing enuff heat to keep the plug clean.----Possible reed valve or lower crank seal issue.----Does spark jump a gap of 3/8" on lower lead ??

 

[AKDan]

I would describe the spark as thready not a pinpoint spark. Don't have any experience with this. Both sparks are similar though.

Last night I did the following:

Spayed a small amount of Powertune into the spark plug holes

It sat for maybe 2 hours.

Reinstalled spark plugs and went to boat launch.

Started motor but took a few pulls.

Let it run rough for 10 minutes till water from tell tale was good and warm. A larger than usual of smoke initially. Would idle at high speed only.

At ten minutes sprayed Deep Creep in carburetor until bogged down. Then ran it for 30 minutes at medium throttle. Ran very smoky and rough. Did not seem to smooth out. so

stopped motor and found both plugs fouled.

Changed both plug and put in another gallon gas with 6 oz of Sea Foam in it and ran for 10 minutes then added another gallon of regular 50-1 mix as smoke was great and rough running.
Smoke had cleared up at full rpm but as I slowed to idle smoke increased to small cloud but somewhat less than normal. Note sea foam increased rpm without a throttle change. Checked idle and would run better but faster in slow idle and pretty fast in fast idle.
It was dark so waited till this morning to look at spark plugs. Lower plug insulator has thin glossy black coating that scrapes of easily. Ground electrode on lower plug has surface changes but is clean. Upper plug totally white insulator with surface changes on ground electrode less than lower plug.

Have video of spark from plugs

Looks like I will go and restart to see if it will start without new plugs.
How much smoke should I expect at idle if it is working correctly?

Thanks again for your input
AKDan

 

[AKDan]

racerone

The spark plugs seemed to be equal and definitely jumped 3/8" inch. With no way to hold them exactly the same distance and or at a stable distance they seemed the same but perhaps the lower one was a little bit less brite. Hard to say.
Thanks again
AKDan

 

[AKDan]

racerone
I've read if reed s are the problem an indicator is that fuel comes out of front of Carburetor. That doesn't seem to be the case as far as a volume of liquid. Might be very slightly damp in the carburetor throat last night. Cold last night as well.
Have been delayed getting back to launch ramp so haven't tried restarting.

AKDan

 

[AKDan]

Hello, flyingscott and racerone

Motor started well. Likely still a little over 2 oz per gallon of Sea Foam in remaining gas/oil mix. At ramp ran fast idle till tell tale solid then 1/2 throttle out to Rainbow trout spot. Was able to troll at low speed for 15 minutes. didn't push it as still a little too fast but no problems running at low idle. Shut it down and used electric trolling motor for about 3 hours. When I left motor started second pull. Seems to be fixed at least relative to operation with Sea Foam in Tank. My season is nearly over so won't get hours on motor till next May. Will likely keep adding Sea Foam 2oz per gallon in all future fuel fill ups.

Thanks for commenting

AKDan