2003 Johnson 175 - Misfire and low compression SEE PIC

Matty3614

Cadet
Joined
May 22, 2011
Messages
16
I have noticed a slight misfire. I did a compression test, and had 110 psi on 5 cylinders, and 90 psi on the lowest port side cylinder. I ordered a powerhead gasket kit. When I opened the cylinder cover I noticed that cooling water had left a crust on the spark plug threads and on the cylinder cover (on the low comp. cylinder). I plan to do the cylinder o-rings and apply new RTV to the water passages. I also have the carb manifolds off for rebuilding. I can see carbon on the pistons and I'd like some advice on removing it.

Can I clean it without removing the pistons?
Is the dry rotted o-ring on that cylinder causing water infiltration to the cylinder which causes the misfire?

SEE PIC.......
 

Attachments

  • 2011-11-27_11-22-23_86.jpg
    2011-11-27_11-22-23_86.jpg
    143 KB · Views: 0

toddschubert

Chief Petty Officer
Joined
Sep 3, 2011
Messages
504
Re: 2003 Johnson 175 - Misfire and low compression SEE PIC

Cylinders look fine from what is vis. in pic. "oring"? what oring are you talking about...where is it? Pistons have rings but not rubber orings that would dry rot. Don't pull pistons unless you are familiar enough and have all proper tools.
Water crust probably due to leaking gasket which you will have to replace.
 

Matty3614

Cadet
Joined
May 22, 2011
Messages
16
Re: 2003 Johnson 175 - Misfire and low compression SEE PIC

The o rings are between the engine block and the block cover. They keep compression in the cylinder and cooling water out. The piston heads look like they have carbon build up on them. Maybe a decarb once reassembled.
 

toddschubert

Chief Petty Officer
Joined
Sep 3, 2011
Messages
504
Re: 2003 Johnson 175 - Misfire and low compression SEE PIC

Got ya. Mine have always just had gaskets between head cover and heads and then head and block. Just replace all gaskets and orings and you should be fine as far as the heads go. Misfire could be any number of other things. Did you try running at idle and pulling one spark plug wire at a time to see if there is NO difference on any ONE of them?
 

Faztbullet

Supreme Mariner
Joined
Mar 2, 2008
Messages
15,589
Re: 2003 Johnson 175 - Misfire and low compression SEE PIC

Usually if a o-ring is leaking on a 60? it will leave a trace on the aluminum surface which I don't see. If bottom cylinder had water intrusion you would see it at the 6 o'clock position as it the only closest place water can enter and piston shows no signs of steam cleaning. If its getting enough water to cause a miss it will be cleaned.

2011-11-27_11-22-23_86.jpg
 

Matty3614

Cadet
Joined
May 22, 2011
Messages
16
Re: 2003 Johnson 175 - Misfire and low compression SEE PIC

Im not sure why the one cylinder would have low compression. Ill do the gaskets and service the Carbs and related power head gaskets. Maybe the carb on the low cylinder is clogged up?
 
Top