Mercury 1993 25 hp 2 strokes compression REsult

hawlisjawt

Cadet
Joined
Nov 2, 2011
Messages
9
Hi,

Made a compression test before motor treatement (sea foam) just to compare after.

Made my test after the motor is warmed.

Tested it at ilde and WOT.

Get the same result 120 and 125 psi to the upper and bottom cylinder. idle and WOT..

I heard that im supposed to get higher result at WOT.

Refer to my manual:

"A reading below 120 psi may indicate a total engine wear problem"

I want to know what ive made wrong or if evreything is normal due to carbon deposit.

Thank you. :confused:
 

Faztbullet

Supreme Mariner
Joined
Mar 2, 2008
Messages
15,589
Re: Mercury 1993 25 hp 2 strokes compression REsult

If you not having any problems dont worry about it, likely the gauge is at fault on same readings. Suggest you try another gauge...
 

hawlisjawt

Cadet
Joined
Nov 2, 2011
Messages
9
Re: Mercury 1993 25 hp 2 strokes compression REsult

My gauge is bran new, but ivew paid it 30 bucks only.

Ill try with another gauge from the job if thread are the same.

Its better now but i have some hesitation at starting when cold.

Yesterday engine start with 8 pull with choe ajustement between pulls, but when it fires he start first time.
 

Texasmark

Supreme Mariner
Joined
Dec 20, 2005
Messages
14,544
Re: Mercury 1993 25 hp 2 strokes compression REsult

I tested my engine recently and it was running 117 and I have the same warning (caution) in my serv. man. This engine runs my boat right at 50 mph at 5600-5800 rpms. Seems that I have adequate compression with my numbers.

HTH,

Mark
 

hawlisjawt

Cadet
Joined
Nov 2, 2011
Messages
9
Re: Mercury 1993 25 hp 2 strokes compression REsult

Thank you for your advice.

My motor is running fine too except minor cold start trouble, ill see if its better after my decarb this weekend.
 

ufm82

Master Chief Petty Officer
Joined
Jul 29, 2003
Messages
827
Re: Mercury 1993 25 hp 2 strokes compression REsult

Two things. 1) How do you check compression at idle and WOT? The plugs have to be out to check compression. Do you mean with the throttle plates open and closed? Compressions checks should only be taken with the butterflies fully open. Other readings are irrelevant. 2) Unless you have severely low compression (which would cause issues everywhere else) is not the sole cause of hard starting cold. It certainly can be but if the engine runs fine at all other times, it's not your problem now. You readings say likewise- no issues there. Hard starting when cold is fuel related- is the bulb priming the carb properly? Is the carb leaking off? Does the choke work? Galley in the carb clogged?
 

JB

Honorary Moderator Emeritus
Joined
Mar 25, 2001
Messages
45,907
Re: Mercury 1993 25 hp 2 strokes compression REsult

Your Service Manuals are wrong unless you are doing the test with their gauges in a shop environment.

Go here: http://forums.iboats.com/showthread.php?t=391323

If all cylinders fit in a 10-15% span and over, say, 100psi, compression is good.

RATZAKRATZA mythology about compression testing and psi causes hundreds of good outboards to be torn down yearly. :(
 

hawlisjawt

Cadet
Joined
Nov 2, 2011
Messages
9
Re: Mercury 1993 25 hp 2 strokes compression REsult

-1 I used JB procedure for my comprtession test.

-2 is the bulb priming the carb properly?

When i pull out primer knob i see a little amount of gaz going out by the little hole a the right of the carb, so i think the fuel bowl is full?

----------
SYMPTOMS OF A DEFECTIVE PRIMER SYSTEM
1. Outboard is hard to start.
a. Diaphragm is cut.
b. Primer check ball is stuck in the closed position.
c. Primer passage is plugged with debris or varnish.
---------

3- Is the carb leaking off?

Had to investigate that.

4- Does the choke work?

While running if a pull out the knob fully, motor is dieing.

5- Galley in the carb clogged?

This saturday ill sea foam my motor.


Thank you for your good words.
 

hawlisjawt

Cadet
Joined
Nov 2, 2011
Messages
9
Re: Mercury 1993 25 hp 2 strokes compression REsult

You got a good point here, because ive made my test at 8 Celcius!!

Your Service Manuals are wrong unless you are doing the test with their gauges in a shop environment.

Go here: http://forums.iboats.com/showthread.php?t=391323

If all cylinders fit in a 10-15% span and over, say, 100psi, compression is good.

RATZAKRATZA mythology about compression testing and psi causes hundreds of good outboards to be torn down yearly. :(
 
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