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Discussion Starter · #1 ·
Hey guys I need your help, I have a 40 hp (3 cylinder) mercury. My wife and I were fishing the jettys this morning when my motor started acting up. It idled fine but when I went to get up on plane it bogged down bad. The max rpms I could increase it to was about 3000. Once reaching 3000 it would surge real bad, going from 3000 to 3800. I limped back to the ramp at about 2000 rpms. and right before I trailered it I throttled down on it again to see what happened and it jumped up to 5500rpms running fine. I ran about 1/2 mile to maybe clear it up but right before I went to trailer it a second time it did it again(bogged down). Once getting home I flushed my motor on the water hose and it started fine and idled fine for about 10 min. The main questions I do have is if it is the carburator will it idle fine and is it possible to get some trash in the carbs that may clear itself. The motor is a 2003 and has never been set up for longer than 4 days; I run it during duck season and fish out of it alot. I failed to mention I did check the fuel for water and there was none. Please help if possible. Thanks Tommy.
 

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Lets see problem #1 could be..
































Its a mercury:slimer:


Easy to fix but may cost more...sell and buy a yammaha!!!!!!!!!
 

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POC chunker
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I would look to these two things. 1) A bad coil/wire/spark plug killing spark to one cylinder. Check the ground wire terminal on each coil, make sure it has a good non-corroded connection to the block. Inspect plug wires and plugs for good connections.

2) Gunk in the carbeurator float bowls that is getting sucked up and blocking a jet in one of the carbs. Drain the float bowls of the carbs, into a glass jar if possible so you can inspect for debris in the fuel.
 

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Full of Surprises!
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I had the same problem on my 1984 Evinrude...............ended up replacing the Power Pack! Now the motor runs flawless.
 

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Could be a bad coil or some ignition part, but it sounds like its a fuel problem. Next time it starts to die or won't pick up hit your choke switch if you have one, if motor improves than its fuel related. Could be a clogged fuel filter, bad primer bulb, dirty carbs, air leak on the fuel line.
 

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Full of Surprises!
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OH might I mention, I replaced bulb, water separator, new spark plugs, and rebuilt both carbs. Trouble shoot the easiest and cheapest route first, because it can get pretty expensive really fast.
 

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Flush gas from the carbs via the drain in the carb bowls and flush and throw out all old gas. Install water/fuel seperator (Academy) and always put in fuel stablizer. Had the same problem and no more ever again...
 

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Three things that have already been mentioned...GROUND/POWER PACK/COILS. However coils normally wouldn't do what you are saying unless they are really messed up. Check all your ground connections, not just for loose, but also for corroded or broken connections.

Something else to look at....STATOR. Take a timming light and put in on the wires...idle the motor up past 3,000 quickly and see if the timming light goes out. Poor man's way of checking the high speed windings. Remember though, you can bench test a stator and be fine...run it on the house...be fine, put the motor in the water, under a load and it won't run.

Doesn't sound fuel related.

Hope this helps,

Dale
 

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lazzer65 said:
Remember though, you can bench test a stator and be fine...run it on the house...be fine, put the motor in the water, under a load and it won't run.
Been there and done that with a Merc. You are exactly right.
 

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Discussion Starter · #12 ·
mercury

First of all I want to say thanks for the help. To give you all a heads up I took my motor today after changing the fuel filter, and it never bogged down. I reached 5500rpms at about a dozen different times. Maybe this was the problem and not just coincidental. I will keep u posted. Thanks again.
 

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Big daddy slim
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i am having the same problem had the carbs done, and a new stator it's about to drive me nuts sometime it does it sometime it dosn't
 

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Discussion Starter · #14 ·
bullred

Yesterday was the first time my motor acted up in this manner, so hopefully changing the filter worked. I guess your motor is still doing it after changing the stator? It is always something. I have had no problems out of my mercury until last week. I started my motor on the water hose and it died, smelling a lot of gas I just took my cowlin off to see what was wrong if anything, believe it or not my fuel lines were busted in three different places????????????????
 

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Discussion Starter · #15 ·
mercury

just got back from flounder gigging and my boat ran like a champ. It is always a better trip when everything goes your way. Even though My wife and I only gigged two 19" flounder it was worth it due to the motor running correctly.
 
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