1986 115 HP Inline 6 cyl - low idle issues

[kotts323]

Bought the above motor last year. Had a mechanic go through it - carb kits, new fuel lines, filters, impeller, new control box, cleaned gas tank. Did not get to run the boat until this season. Having issues starting the boat in low idle/neutral position, need to push up the throttle to get the boat started. Bring the throttle back down, it will stall unless I punch it quickly into gear. Once in gear, all is good. Back down into idle, and stall. Also, on a couple of occasions, the ball has lost pressure.
Not very good with motors, so any suggestions for easy tests or fixes I could try would be appreciated before I spend more money at the mechanic. I know that there is an enricher. When I turn the key, and press it in, I can hear it engage and gas is moving to the motor. Been using high octane gas, marine Stabil with every fill up. A couple of guys suggested that maybe the mechanic did not set the carbs correctly after rebuild, and then someone else suggested idle timing due to new control box. Any thoughts appreciated.

 

[calvinator]

I have an inline 6 I spent a lot of time getting to run correct.

Mine would die at idle like yours. At idle/low RPMs, the carburetors are using the carb idle circuit to supply fuel/air to the motor. When there is not enough fuel in the fuel/air mix, the motor will stall. Pretty common problem.

The fuel/air mixture is controlled by a screw on the front of each carb. Search for idle mixture screw, you'll find a bunch of info on how it works and how to set it. Turning the screw clockwise leans the fuel, turning the screw counterclockwise richens the fuel. You'll want to richen the fuel mix at idle speeds -- read up on that.

Another pointer.....the idle mix needs to be set with the boat in the water and in forward gear. You need the water pressure and prop load on the engine to get the idle correct. You can't successfully set the idle mix in your driveway using a water hose connected to the motor (no load on the motor). You need to be tied to a dock, on the trailer, or in a test tank to set the idle properly.


And the enricher.... This is nothing more than a valve that opens and flows gas to the intake to help you start a cold motor. Enricher is not your problem once the motor is running.

Dialing in your motor takes a few hours and is a huge sense of accomplishment! But if you take it back to the mechanic, I would have them set the idle mix in a test tank before they start tearing into anything else. This should take only a couple of labor hours.

Good luck with it !!

 

[schematic]

someone else suggested idle timing due to new control box. Any thoughts appreciated.

new control box would not cause idle to go LOW unless it was mal-adjusted to begin with.....

 

[kotts323]

Thank you guys for the info. Looks like I have a little homework to do before I get to the lake this weekend. Calvinator - thanks for the detailed response, gives me plenty to work with.

 

[cheers731]

Hi Folks,

I have bought a boat recently with the same outboard. The idle rpm is around 1400, is it too high? I am used to see 600 rpm with an I/O engine.

 

[calvinator]

Hi Folks,

I have bought a boat recently with the same outboard. The idle rpm is around 1400, is it too high? I am used to see 600 rpm with an I/O engine.

Yes, 1400 RPM in idle is too high. Needs to be under 800-1000RPM in neutral, and 600-900RPM in gear. Otherwise, you are straining your lower unit gears when shifting --- you'll be hearing a clunk.

Some things to investigate:
a) are your throttle cables adjusted properly.
b) is your idle stop screw set correctly.

Check these two items first. They are related. Your best approach is to remove the throttle cable, then investigate your idle stop screw setting. If you are able to achieve the proper idle with the stop screw, adjusting the throttle cable is simple.

Good luck with it all !

 

[cheers731]

Thank you so much, it's very helpful. This is my first outboard, lots for me to learn.