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1992 40hp merc 4cylinder

Discussion Forum at MarineEngine.com » Mercury Mariner Outboard » Archive through July 09, 2009 » 1992 40hp merc 4cylinder « Previous Next »

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RICHARD FITCH
New member
Username: godsin

Post Number: 3
Registered: 04-2009
Posted on Wednesday, July 08, 2009 - 11:25 pm:   Edit Post Delete Post View Post/Check IP

If you run motor with ear muffs on it revs up just fine ....put it in the water and you can only get quater to half throttle and it dies out but once in a while it takes off runs fine next time dies out right away?????
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Benjamin Jones
Advanced Member
Username: benjamin_jones

Post Number: 275
Registered: 04-2008


Posted on Thursday, July 09, 2009 - 11:03 am:   Edit Post Delete Post View Post/Check IP

Compression good?
When was last service?
Condition of fuel?


Too many variables here, we need more specifics as to history of motor.

Ta!
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RICHARD FITCH
Member
Username: godsin

Post Number: 4
Registered: 04-2009
Posted on Thursday, July 09, 2009 - 11:48 am:   Edit Post Delete Post View Post/Check IP

Compression was good all 4 cylinders were 105 to 110
Took it in week ago have another apointment.... he said all he did was screw the carburator screws all the way in and back out and it ran fine for about 20mins on my first trip out.
I check spark turning it over it sparks good on each cylinder ...
Would the triggers work fine with muffs on and not work when you put a load on it? There is a rattle or knocking noise now at top of the motor and to me it sounds like its either behind top carburator or close to flywheel???
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Graham Lamb
Senior Member
Username: galamb

Post Number: 5592
Registered: 05-2007


Posted on Thursday, July 09, 2009 - 12:20 pm:   Edit Post Delete Post View Post/Check IP

If trigger works fine on muffs it will work fine on the water - either works or doesn't.

The rattle/knocking noise could be many things. If the motor is still sluggish under load that knocking could be a bad crank bearing. If that was the case you would be losing crankcase pressure through the bad seal which could explain the lack of power under load.

But that really is speculation on my part. Most times loss of power under load is due to a clogged carb(s).....

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