Johnson 25 hp fouling bottom plug...

Subtle

Seaman Apprentice
Joined
Oct 5, 2013
Messages
38
If the lower seal is busted you wont get crankcase compression and therefore fuel would never make it to your lower plug and make it wet.

Do this,
1) run the outboard and then remove the wet plugs. Light the wetness, if it does not go poof then it is wet with fuel and water. This happens a lot and is caused by a exhaust gasket leak in most instances.

2)Next do a spark test by jumping a 7/16 gap. If it does not do that on both cylinders then report back and we can go from there.

Once you report back on 1 and 2 then it will be clear what is wrong. DO NOT GET SIDETRACKED AGAIN otherwise you will spend big bucks which if you are like me means less to spend on the ladies


Where is the exhaust gasket? Thats not the powerhead to midsection gasket is it?
 

Subtle

Seaman Apprentice
Joined
Oct 5, 2013
Messages
38
Spark will jump 7/16. Cleaned both plugs with carb cleaner, sprayed with air to dry. Bottom plug is no longer coming out wet, but its still not firing... Top plug wire off with bottom on and the engine wont fire, top wire on with bottom one off and it will start up on that one cylinder... neither plug when held to flame did anything.
 

Bosunsmate

Admiral
Joined
Apr 7, 2012
Messages
6,129
Where is the exhaust gasket? Thats not the powerhead to midsection gasket is it?
No thats commonly called the adaptor plate or powerhead gasket
EXHAUST PLATE is on the port side near the rear, the big long rectangle
 

Bosunsmate

Admiral
Joined
Apr 7, 2012
Messages
6,129
Spark will jump 7/16. Cleaned both plugs with carb cleaner, sprayed with air to dry. Bottom plug is no longer coming out wet, but its still not firing... Top plug wire off with bottom on and the engine wont fire, top wire on with bottom one off and it will start up on that one cylinder... neither plug when held to flame did anything.

Keep plug boots off and grounded and then with the water running on the hose or however you are doing it, in a barrel whatever, turn the engine over for a about 5 secs with the starter, then stop and give it thirty seconds to cool down the starter then do that again then remove a spark plug, it should be wet with fuel, light it and it should go poof in combustion straight away, do that again with the next plug.

If it doesnt go poof then you have fuel problems most likely it would be water in your fuel, either from your tank or somewhere in your motor
 
Last edited:

racerone

Supreme Mariner
Joined
Dec 28, 2013
Messages
36,047
I think this motor needs to be torn down for a new piston / s and rings.---Possibly o / s parts.--Perhaps a visit to the seller.----Once again proves that motors sold privately are being sold for a reason.
 

Subtle

Seaman Apprentice
Joined
Oct 5, 2013
Messages
38
Keep plug boots off and grounded and then with the water running on the hose or however you are doing it, in a barrel whatever, turn the engine over for a about 5 secs with the starter, then stop and give it thirty seconds to cool down the starter then do that again then remove a spark plug, it should be wet with fuel, light it and it should go poof in combustion straight away, do that again with the next plug.

If it doesnt go poof then you have fuel problems most likely it would be water in your fuel, either from your tank or somewhere in your motor

mines pull start. :(
 

Subtle

Seaman Apprentice
Joined
Oct 5, 2013
Messages
38
Is this why it will not run on that cylinder or is there another reason! I don't want to rebuilt it if i can get buy using it until I can afford a brand new one...
 

Bosunsmate

Admiral
Joined
Apr 7, 2012
Messages
6,129
Did you press those rings in to see if the are bendy ie still intact?
My 60hp has scored cylinder walls from an overheat but still goes like a cut snake
 

Bosunsmate

Admiral
Joined
Apr 7, 2012
Messages
6,129
You have 110 compression on that cylinder, so that scoring aint your problem for why its not firing. Mine has only 102
 

Subtle

Seaman Apprentice
Joined
Oct 5, 2013
Messages
38
The only things I haven't checked is the head gasket the timing. And the carb. Scoring comes from not enough lube correct. Timing couldn't cause scoring. Does this mean that my carb isn't working correctly. And with my intake and exhaust gaskets working like they should of can a head gasket cause my bottom cylinder not to fire? I just don't understand. The way the fuel enters the engine it has no choice but to get to both cylinders. And with my spark working. What else is there?
 

racerone

Supreme Mariner
Joined
Dec 28, 2013
Messages
36,047
The scoring I see is on the " cool side " of the motor.---My bet is that the exhaust side is worse.------Did you not see the scoring in the cylinder when head was off ?----This motor needs to be rebuilt !!!!!
 

Subtle

Seaman Apprentice
Joined
Oct 5, 2013
Messages
38
i pulled the other side to it was actually not as bad as the intake side... dont know why but it wasnt...
 
Top