Logo
FULL SITE MENU

'86 Merc 60hp 3 Cyl. Idle Question

F

FishinLite

Regular Contributor
I am fairly new to outboards but not unfamiliar with small engines. So here I go. I have my Merc mounted on a engine stand with all the control connected. I am restoring my boat and I worked on the motor over the winter. Ultrasonically cleaned the carbs, replaces the fuel lines, replaces the plug wires (they were originals), replaced the wires between the CDI and coils (they were down to 3 or 4 strands), new water pump, and added some parts that a previous owner had left out, cleaned, cleaned and cleaned.

I installed the muffs, and set the low speed mixture screw to 1 1/2 turns out, connected the mini-tach to Cyl#1 plug wire, and fired it up.

I adjusted the mixture screws 1/8 of a turn at a time monitoring the mini-tach. I adjusted them for maximum rpm. With both carbs set for max rpm, I opened them about 1/4 turn. The RPM dropped about 10-15 rpm.

"Fast Jeff" writes about setting this engine configuration with an infrared temp gun. To make sure that I have the carbs set correctly get out my infrared temp gun.
Cyl #1 - 97.4 degF.
Cyl #2 - 94.3 degF.
Cyl #3 - 93.6 degF.

Now the question is ... Is the upper carb set to lean? or to rich? Is there a better way to do this?

Any input would be appreciated, thanks
 
Those need to be adjusted on a warm engine on the lake not on muffs. You cannot get a correct temp reading on muffs maximum temp will occur after a WOT run. There will be a temp difference between cylinders it is normal you really cant adjust carbs from the temp.
 
Last edited:
Flying, ideally the motor would be on the lake or in a tank, but to get a good initial setting you have to start from somewhere. At Idle, when you start your motor it isn't in gear, the only load on the motor is the water pump (there is very little difference between the muffs and lake). I wasn't looking for max cylinder temperature. Being an retired engineer I may be over thinking this, but i was looking for a perfect idle setting.

When you start looking a carb flow curve they look some think like this:
Carb_Flow_1.jpg
Carb_Flow_2.jpg

When you go to start you outboard or are trolling for fish, you are at the very bottom of the curve. The only thing that you have to control the quality of operation is the mixture needles. The only way I can think of to check the balance of the two carbs feeding three cylinders is temperature.

So my original question still stands.

Now the question is ... Is the upper carb set to lean? or to rich? Is there a better way to do this?
 
You are overthinking this you need a FACTORY MANUAL. Big difference between running on muffs and the lake on muffs you have no exhaust back pressure which it needs. On muffs you will have a higher idle because of the lack of back pressure and the carbs run lean because of that. On outboard motors the idle is set when the motor is running,warm and in gear this where you will get your idle optimized . The motor needs to have a link and sync done which will be covered in the manual. The only thing muffs are good for is to tell you it runs. There is a reason most shops have test props and tanks. After you get the manual and everything is good it's time to go to the lake. When I do it I set the low speed screws to 1.5 turns out so it will start then I am off to the lake. Also give your serial #.
 
Last edited:
Correct. You need the LU in a bucket, or on the boat, to provide enough back pressure.

Your temperatures are so close (if the LU was in a bucket or etc,.) that you'd be in good shape. And don't forget the extra 1/4 turn OUT (CCW) when you're done.

Ain't this fun!

Jeff
 
Thanks all for the input.
The serial no. is 0A110380.
I am still working on my boat restoration, so it will be a month before the motor is remounted and in the water.
Pictures to follow when it in the water.
Thanks again.
 
Back
Top