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Old 07-15-2011, 01:38 AM   #1
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Default rough idle

hello, i have a 2006 maxum 1800mx with a 135 hp mercury engine and it is very hard to start and it runs very rough. the rpm gauge says that the rpm is between 250 and 350 which i think is very low i am thinking at least 500 rpm. the engine itself is very clean and once you hit the throttle it goes with no problem and all of the spark plugs are good and working. what i thought is to change the fuel filter because it maybe be clogged. it probably has never been changed. also how often should you change the fuel filter, i am thinking every three oil changes that what i do with my car. what about those fuel cleaners you put in your gas tank to clean the fuel system does it actually work?

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Old 07-15-2011, 02:00 AM   #2
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http://www.maxumownersclub.com/forum...6568&noquote=1 I change the fuel filter every year. There are lots of possibilities besides bad fuel. Change plugs and make sure gap is correct. If carbureted make sure the distributor cap and rotor look good. There is an electronic sensor in some distributors , replace it if in doubt. With ethanol your carb could be gunked up too, if so it can be rebuilt for around $200ish. It's probably either a fuel issue or a spark problem...
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Old 07-15-2011, 04:10 AM   #3
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i runs perfect when you go open throttle and it does start, it takes about 5 seconds to start and i don't know if that is normal or not. i was thinking about adjusting the throttle to open it just until the idle reaches 500rpm.
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Old 07-15-2011, 03:37 PM   #4
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Is this a new issue or has it been going on for a while? How many hours are on the engine?

Assuming your tach is accurate 300 RPM's is too low. Should be closer to 600 or so. Is this a carbed engine or fuel injected?

Your symptom is not being caused by a clogged fuel filter. If the filter was clogged you would be having problems at higher RPM's where the engine require more fuel flow.

As Capt Al mentioned, check the dist cap and rotor, but I doubt that's the issue.

Need to know if it's carbed or injected.....
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Old 07-15-2011, 06:40 PM   #5
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I have used Sea Foam in all my engines for years. I dump a gallon in each tank on the boat once a year.
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Old 07-15-2011, 09:37 PM   #6
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well...baring any other problems....if the plugs and everything else is fine.....then adjust the idle screw to 600-650 rpm....is this a carb'd engine or mpi??...if it's a carb...you can adjust the idle.....if it's mpi..a tech with computer needs to adjust it...


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Old 07-15-2011, 10:43 PM   #7
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yes it is a carb'd engine. so adjusting the idle screw should fix this problem right. but the higher rpm the more the gears wear out when you put it in gear.
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Old 07-18-2011, 01:52 PM   #8
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Technically true, but the engine and drive were designed to idle at a certain speed. Might consider finding the manual for your engine/drive combo and find out what the idle speed is supposed to be. My guess is something closer to 600.
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Old 07-18-2011, 04:11 PM   #9
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I had a similar problem on my 92 Maxum 2100SC (4.3L) (ruff idle, and RPM surging at low RPM's. Rebuilt the Carb and runs great now, (Make sure you adj the float properly) Mechanic at the Boat yard said the Ethanol in the Fuel causes some seals to break down and clog up the idle Ports, jets, float needle... etc. Just my 2 cents! Oh BTW my Idle RPM is set BTWN 650 - 700.
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