1980 - Merc 115 inlines 6 - Stalling under load

[hempfarmer]

Hi everyone,

I just picked up a new ski boat with a Merc 115 inline 6. Generally runs great except when I am trying to pull a skier. I have to have RPM's at 1200 before I can punch it when towing a skier. If I punch it at 1000 it will stall each time.

Anyone familiar with this problem and what I might want to adjust?

Thank you.

Randy

 

[Chris1956]

Re: 1980 - Merc 115 inlines 6 - Stalling under load

If the carbs are clean. it is likely the idle mixture is a bit lean. Open the carbs 1/8 turn, one at a time starting from the top carb, and test it after each adjustment.

 

[hempfarmer]

Re: 1980 - Merc 115 inlines 6 - Stalling under load

Carbs were rebuilt and boat serviced by an experienced mechanic this winter. He could only test it in the tub so maybe it was hard to adjust the carbs properly. I will give that adjustment a try, may just save me a 3 hour drive to the mechanic.

Thank you!

 

[hempfarmer]

Re: 1980 - Merc 115 inlines 6 - Stalling under load

Curious, anyone know if there is a way to simulate "load" when running the engine in a big tub?

 

[hempfarmer]

Re: 1980 - Merc 115 inlines 6 - Stalling under load

If the carbs are clean. it is likely the idle mixture is a bit lean. Open the carbs 1/8 turn, one at a time starting from the top carb, and test it after each adjustment.

Oh yeah, which way do I turn the screw?
Thanks!

 

[verado7]

Re: 1980 - Merc 115 inlines 6 - Stalling under load

turn the screw left to richen .- the idle mix is important for hole shot right up to mid range then the main jets take over - you need to adjust mixture with boat in gear in the water - a tub wont cut it - except to get it running . i would start over one carb at atime turn the screws left slowly til rpms go up and then just as they fall (make avisual note ) then turn right -rpm's go up then just as they fall turn back approximately half way to the visual refrence yuo took when turning left.

 

[Chris1956]

Re: 1980 - Merc 115 inlines 6 - Stalling under load

Verado has described the Service manual way to adjust the carbs. I never had luck with that method. Since you are real close with the current carb settings, I would stick with the procedure I described. Richening the mixture means turn the idle mixture screw CCW. 1/8 at a time to avoid messing it up completely.

BTW- Carb Main jets take over at 1200-1500RPM or so. Idle jets have no effect at that RPM or higher RPMs.

 

[hempfarmer]

Re: 1980 - Merc 115 inlines 6 - Stalling under load

Thanks for all the information, very helpful everyone!

One other question, is there a best practive for making these adjustments while in the water? Unless I am misunderstanding I should have the boat in the water and put it in gear when adjusting the carbs?

 

[Chris1956]

Re: 1980 - Merc 115 inlines 6 - Stalling under load

That is the best way. Leave the wrap cowl off and do the adjustment. It is easiest if you have a driver.

 

[sschefer]

Re: 1980 - Merc 115 inlines 6 - Stalling under load

That bog comming off idle can be carb adjustment and most everybody jumps to that. I often find it's too much timing before the carbs open and a simple link/synch procedure cures it.