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planebrutal

1998 Mercury 225

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Motor seems to be idling way to high when putting in to gear it chunks hard any ideas how to adjust

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What RPM is it at in neutral?

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I'm not a mercury person but yes, that is way too high. As for how to adjust it, I would recommend getting a the factory service manual if you are going to be doing much work on it yourself. There are several ways you can idle it down, and most are wrong and the factory manuals are fairly cheap, usually about $35. One of those Clymor or what ever they are called will work but they cost almost as much as the factory manual and no where near as good.

The first thing you need to do is a check all the linkage marks and make sure everything is where it suppose to be, someone before you may have already tried and gotten things out of whack.

A couple of things you can check, if running a Hotfoot, make sure it's letting it fully return. Normally the easiest way to eliminate a possible miss adjusted cable is just to disconnect it from the motor and then use you hand and push/pull the linkage to it's idle stop. If it idles normal doing that, you need to adjust the end that connects onto the motor.

As for trying to turn anything on the motor without the book, I wouldn't do that. Every motor I get, I do a link and sinc on them because about 95% them someone has already been turning on things they weren't suppose to.

One word of advice, DO NOT try adjusting the idle anywhere but in the water with the motor at it's normal depth. You MUST have that back pressure on it. If you try and doing it out of the water it will idle way too high.

Also, a lot of mercs run an idle control module that could be giving problem, but again, get the manual first.

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Best way to rebuild an outboard is to mess with the throttle linkage not knowing what you are doing.  This from someone who found out the hard way fooling with a 115 tower of power many years ago.  Get a manual or take it to someone who knows what they are doing.

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What should the idel speed be my boat is 18 for 9 in and it slow as I can go is about 5.6 mph witch make it tough to load

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Again, the manual will have the recommend rpm, but in gear,  I would probably be somewhere around 700 rpm.

 

If it's as high as you are saying, either someone has been turning things and didn't know what they were doing or it's being held by the throttle cable for some reason.  Start off by taking the throttle cable loose from the motor, that's usually a very easy process on a Merc, and hold the linkage against the stop. 

 

Is carbs or EFi?  I know a lot of the carbs run that idle control module and they do go bad.

 

You can check things and do a link and sinc on the muffs, you just can't make your idle speed adjustment until it's in the water, and then you will do it in gear.

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Probably around 750 rpm in gear.  That will be in the manual, and I can't stress enough, other than checking the cable, don't screw with it if you don't know exactly what you are doing.

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You can do this out of the water, you just have to take into consideration that the rpm are going to drop with the added back pressure so you will have to set it higher out of the water than when it's in. I don't remember if those have an idle set screw like the carbureted motors do. If it does it'll be pretty evident as it's a screw that adjusts how far the throttle can go back on the side of the engine. Engine RPM should be close to 1000 in neutral. The clunk you here is normal though, although in your case probably a little more severe. If you can't figure it out yourself, or you doubt your knowledge be safe and take it to a dealer.  

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As I have stated many times, I'm not a merc guy, but I would think 1,000 in neutral to be rather high on a good motor. I usually expect more than about a 50 rpm drop when in gear. It my be 2000 for all I know about merc, so not trying to start anything, just stating my thoughts.

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225 sounds big for a 18'9 boat our old bee was 18'6 and only rated for a 150. Anyway our yamaha idles at 900 and then drops to about 600 when in gear try trimming your motor up when at idle. If ours is trimmed down it chunks real bad and will cut off if if left for a while.

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As I have stated many times, I'm not a merc guy, but I would think 1,000 in neutral to be rather high on a good motor. I usually expect more than about a 50 rpm drop when in gear. It my be 2000 for all I know about merc, so not trying to start anything, just stating my thoughts.

 

Most outboards, regardless of brand, are right in that range. You drop far more that 50 rpms when put into gear. It's usually a few hundred at least depending on how low your motor is in the water. Those of us that have hydraulic jack plates will have more back pressure than those who don't.  

 

225 sounds big for a 18'9 boat our old bee was 18'6 and only rated for a 150. Anyway our yamaha idles at 900 and then drops to about 600 when in gear try trimming your motor up when at idle. If ours is trimmed down it chunks real bad and will cut off if if left for a while.

That's a good indication that you should bump your idle up just slightly.

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