1996 Mecury 40hp 4cylinder carb adjustment

[gt4turbo78]

HI, I have a 1996 Mercury 40hp, 2 stroke 4 cylinder outboard. I recently did a carb rebuild. The motor runs pretty good but I am wondering what the carb setting should be on the adjustment screw? I have the screw out a little more than flush from the carb housing, I can't remember exactly how many turns out it is though. Also, is there any other way to adjust the idle on these carbs?

Thanks,

John

 

[SC1650]

Re: 1996 Mecury 40hp 4cylinder carb adjustment

I assume that your carbs are the same as mine on my 1992 40 HP 4 cylinder. There should be two carbs, each feeding two cylinders. According to my book, which goes to the 1994 model you turn the idle adjustment out 1 and 1/2 turns from a lightly closed position. This is the initial setting. Also according to my manual you should have the engine running with the boat in the water and have the engine up to operating temperature. Have the engine in forward gear when performing these adjustments. You then turn the idle adjustment screw out until the engine starts to load up or start to fire unevenly by creating a rich condition. Turn the screw back in until the idle levels out. Note that position. You now screw the idle screw in until you get a misfire due to the lean condition. Once you get to that point, back the screw out until the engine runs evenly. Note that position also. They state in the book to pick a point midway between these two positions and leave it. If you want to change the idle mixture, they prefer a point just a little toward the rich side as a lean condition will cause hard starting.

It may take you a couple of times adjusting due to the two carb setup but once you have it, the engine should run like a top.

Hope this helps. There is no other idle adjustment on these carbs. Only other adjustment is the screw to stop the engine from over revving and that has to be done with the engine at WOT and in gear. Not something I would want to try.

Steve

 

[gt4turbo78]

Re: 1996 Mecury 40hp 4cylinder carb adjustment

Thank you Steve for that information. I will try doing that this weekend. I'm pretty sure the screw is currently out 2.5-3 turns. I knew i was running a little rich as gas consumption was a bit worse the last time out on the water.

Thanks again,

John

 

[inchesechoes]

Re: 1996 Mecury 40hp 4cylinder carb adjustment

Steve,

Read your reply from back in May 2010. I put a thread out today regarding the purchase of a boat with a 1992 Mercury 4 cylinder as you referenced having one of your own. Can you give me any advice as to me purchasing 92 Merc 4 cylinder. What to look for, good or bad when I check it out.

Thanks

inchesechoes

 

[jeffersondodson561]

Re: 1996 Mecury 40hp 4cylinder carb adjustment

is your sync and link correct, do all of your throttle plates open at the same time?