Mercury inline 6 idle problem

I have a 1983 115 hp inline 6 Mercury outboard that was rebuilt last year and I haven't been able to get it to idle smoothly since. Runs great on top end and sometimes it will idle normal but often it wants to die when you bring it back to idle - especially after it has been run awhile and you bring it back down to idle. Kind of annoying when coming up to the dock. I also have to use the "cold start" most all times for starting. Without the extra throttle it just won't keep running enough to shift into gear. <br /><br />I have tried to adjust the air mixture screw on the carburetors which I know affects the idle but to no avail. The pressure in my fuel system is good (the bulb stays up) but I am wondering about my fuel pump. Last week end I pulled off the line coming from the fuel pump and when I pumped the bulb I got good fuel flow but when I turned over the engine the flow was eratic (and light) coming from the pump. I had the fuel pump rebuilt 5 or 6 years ago but I wonder if it might be my idle problem. But it seems to me if the fuel pump was weak I would notice on the top end as well. I can run this engine at 5600 rpm (if my tach is right) which is on the high side for the inline 6 which to me doesn't fit a weak fuel pump problem.<br /><br />But a fuel pump rebuild kit is pretty inexpensive and easy to do. Does it make sense to try that before digging into the carbs? Or could it be something else? Any thoughts? I am longing to come idling smoothly up to the dock once again.

Re: Mercury inline 6 idle problem

Welcome kc. Have you tried setting the idle up any to see if that helps? Maybe it's just not set high enough. I have a '86 inline and I know that mine idles real low.<br />It's bad if you have to use the fast idle lever and put in gear at same time. It is not meant to work that way. Hard on lower unit gears.<br />I would check the idle screw and see if that will solve it for you.<br />Hey some one else will pipe in here shortly.<br />Good luck.<br />Got to love them inlines.

Re: Mercury inline 6 idle problem

for Price I did start right where you said.<br />Rex

Re: Mercury inline 6 idle problem

I don't believe it is the idle adjustment - sometimes she idles fine. Even though I rarely can start it and put it into gear without it dying maybe the idle adjustment should be bumped up some. I am trying to remember what she idles at -- seems like it is around 800 rpm. I know when I watch the tach and she doesn't want to idle it drops off but should she be set to idle higher than 800 rpm? I am not sure of the spec.<br /><br />Thanks for the reply and I love my inline Merc. I have had this motor since '90 and have put a lot of hours on her with very little trouble. Did have a piston drop on me early last year but it wasn't too bad to have her gone through. Just have that elusive idle problem to go!

Re: Mercury inline 6 idle problem

I have almost the same exact problem as kcrafton. I just bought the boat and never owned one before. I don't know what to do? Sometimes it idles fine. Sometimes I've ran it for 15-20 minutes half a dozen time during the day and run into a idle problem. I always let it warm up for a couple minutes and when I get to around mid speed it sometimes will loose power and die. The prevoius owner didn't have to fix anything in 8 years. what should I have done to this motor?

Re: Mercury inline 6 idle problem

There are a number of things that can each contribute to an idle problem

Fuel pump diaphragm hardening from alcohol in the fuel, works fine with the high pressure/vacuum pulses of WOT but restricts movement at low pressure/vacuum it idle, fails to provide low RPM pressure and flow, the upper carb runs out of fuel.

Small air leak into fuel line before the fuel pump, similar effect as above.

Inconsistent fuel/oil mixture varies the idle quality/speed.

Idle timing slightly retarded.

Carb synch even slightly amiss during the last link & synch.