mercarb adjustment

[joe average]

1991 searay 185 4.3 mercruiser 450 hours 2 barrel mercarb. I just overhauled the carb due to a hesitation on acceleration and inability to run smoothly at wot last season. Was full of crap when I dismantled it. I also installed a fuel filter/water seperator before reinstalling the overhauled carb. Runs GREAT now. What is the proper technique for adjustment of the idle? There is one idle screw and then the (throttle return stop screw?) on the linkage. I initially had the idle screw set at 2 turns out per instructions but the engine was idling too slow and eventually dying. I backed the screw out one-half turn which seemed to have no affect, so I turned the (throttle return stop screw?) in 1 turn which has it now idling smoothly at about 800. Seems to work like this but is it right adjusting it that way?<br />thanks, Joe

 

[Mahoney]

Re: mercarb adjustment

I believe the correct way to do the idle adjustment is to begin with the idle stop screw. Adjust that so you are at your correct idle speed. When the engine warms up(choke off) check idle and idle stop screw to bring it into the correct range. Fast idle adjustment is a different proceedure.<br /><br />Once you are in the correct range adjust the idle mixture screws to get the highest rpm(you might have them right where they need to be, and might not) adjusting them may pick up 50 rpm due to a more optimal mixture.<br /><br />If that is the case, adjust idle mixture screws to highest rpm you can achieve then back the idle throttle screw back down to the correct range.<br /><br />Make sure your timing is on as well.

 

[Manipulator]

Re: mercarb adjustment

By idle screw I assume you are talking about the "mixture" screw. I believe the best way to do this is with a vacuum gauge. I'm going to do that later today. I have a Sea Ray too and just rebuilt the carb. I have a Rochester Quadra jet (4 barrel). Anyway, I would like the exact procedure too. From what I understand you back the idle screws out until there is a drop in vacuum and then screw them in 1-2 turns. My carb has 2 mixture screws (one for each barrel on the primaries). More suggestions I hope are on the way.

 

[trog100]

Re: mercarb adjustment

the highest vacuum reading would simply mean the hightes rpm for a given size throttle opening.. your ears should tell u pretty much the same thing.. <br /><br />first.. adjust the thottle stop screw till your engine idles somewhere vaguely right.. then turn in or out the mixture screw.. if it slows down or the vacuum reading drops go the other way.. find the sweet spot in the middle.. the highest vacuum reading or highest engine rpm is what u are looking for.. the idle mixture is then about right..<br /><br />after this u adjust the throttle stop screw till your engine idle rpm is what it should be..<br /><br />one thing to watch for is that the throttle lever is firmly against the stop screw when the throttle is closed.. sometimes the rest of the linkage holds it slightly off and it doesnt always return to where it should be every time.. push firmly against it.. u should not be able to make the engine slow down any more by doing this..<br /><br />i recon this is another thing that folks think is more complicated than it really is.. <br /><br />trog100

 

[joe average]

Re: mercarb adjustment

I get it! Thanks.<br />Joe

 

[joe average]

Re: mercarb adjustment

I get it! Thanks.<br />Joe