04 merc 25 HP 2 stroke. Dead on one cylinder

[deadmerc52]

I just got a 25 HP merc that was supposed to run fine. 2 stroke, single carb with good compression and what looks like good spark at the new plugs. Lower cylinder is dead at idle and it comes and goes at higher RPM. Plug is dry and cool and it does not blow back through the carb. Also, there is a lot of gray foamy goo at the prop exhaust. . Any help on what to check would be appreciated. Thanks

 

[Sunfish12]

Re: 04 merc 25 HP 2 stroke. Dead on one cylinder

How do you know lower cylinder is the issue?

 

[Wingedwheel]

Re: 04 merc 25 HP 2 stroke. Dead on one cylinder

Gray foamy goo sounds like water mixed with un-burnt fuel mix. Is your plug in the cylinder thats not firing really clean? does it look like it might be wet?

 

[Maxz695]

Re: 04 merc 25 HP 2 stroke. Dead on one cylinder

Hopefully it,s not water if it is your gonna have to get a full head set and replace the exhaust gasket the base gasket where the water jacket enters the engine. but by pulling the powerhead you might as well do all the gaskets. You say you have fire on both plugs so my guess is a bad gasket or a rotted exhaust port plate. not exactly like your but you get the driftView attachment 92026View attachment 92027View attachment 92028View attachment 92029View attachment 92030

 

[deadmerc52]

Re: 04 merc 25 HP 2 stroke. Dead on one cylinder

How do you know lower cylinder is the issue?

I pulled the bottom plug wire off and it made no difference. If I pull the top plug wire, it will die. it is a new plug an appears dry.

 

[deadmerc52]

Re: 04 merc 25 HP 2 stroke. Dead on one cylinder

Hopefully it,s not water if it is your gonna have to get a full head set and replace the exhaust gasket the base gasket where the water jacket enters the engine. but by pulling the powerhead you might as well do all the gaskets. You say you have fire on both plugs so my guess is a bad gasket or a rotted exhaust port plate. not exactly like your but you get the driftView attachment 92026View attachment 92027View attachment 92028View attachment 92029View attachment 92030

Any way to isolate this before removing the power head

 

[Wingedwheel]

Re: 04 merc 25 HP 2 stroke. Dead on one cylinder

Have you checked your coils?

 

[deadmerc52]

Re: 04 merc 25 HP 2 stroke. Dead on one cylinder

Have you checked your coils?

Yes, both coils read about the same. About 3-4 ohms on the primary and around 890 on the seconday. compression is about 115 on both. When I pull the wire at idle and put it back on, it will fire momentarily. Thanks

 

[Maxz695]

Re: 04 merc 25 HP 2 stroke. Dead on one cylinder

1 cylinder is not firing more than likely due to water in the one cylinder. Few questions Do you use this in salt water alot? Do you flush the engine regularly? Find out if your compression should be 120. With a new plug does it run ok for a minute or so?

 

[deadmerc52]

Re: 04 merc 25 HP 2 stroke. Dead on one cylinder

Hi, just got the motor last week. ran it on muffs then and did not notice this problem. It was used in fresh water, will not run on lower cylinder at all with new plugs. Ran with new plugs for about ten minutes at high idle, top plug showed normal signs of combustion, lower plug was clean and dry. Thanks

 

[Maxz695]

Re: 04 merc 25 HP 2 stroke. Dead on one cylinder

well at least the plug is dry. thats a plus take to plug out and test the spark at a 7/16th inch gap for bright blue spark arch. If it is not bright blue witha pop sound than you have weak spark to that cylinder. test the stator and the switchbox. tests are in your manual.

 

[Faztbullet]

Re: 04 merc 25 HP 2 stroke. Dead on one cylinder

Flip the primary wire to the coils(1 to 2 -2 to 1) and see if problem follows the wire or coil.

 

[deadmerc52]

Re: 04 merc 25 HP 2 stroke. Dead on one cylinder

I tried everything mentioned in this thread except for gaskets ,nothing has helped and I ran out of time to work on this. I took the black anchor to the dealer, we will see what he comes up with. thanks for every ones help. I will post what he finds.