Merc 115 Carb Floats?

[metalvolks]

Hey,

I rebuilt my carbs on my '82 115 a month ago. It ran and idled perfectly for 4 or 5 outings only to go back to doing what it did before I rebuilt the carbs (surging, giving it gas and it takes a few seconds to respond, bogging down and dying when giving it gas, hard hard starting, and missing idle). Sometimes it acts like its too rich and sometimes it acts like its too lean.

First, my question is: do you have to measure the float to needle valve distance and adjust (like you do on car carbs)?

2nd question: I have replaced all fuel lines, cleaned out main fuel tank, new gas and it still acts up. I even added an inline fuel filter before the pump. Do you think there is still something clogging one of my idle or main jets? or making the needle valve stick open? poorly adjusted floats?

This problem seems to happen all of a sudden and then sometimes just goes away only to come back hours later all of a sudden.

Thanks for any advice...

Paul

 

[hkeiner]

Re: Merc 115 Carb Floats?

Response to 1st question: A shop manual for your motor would describe how to set the float levels for your particular carbs. Since you already rebuilt the carbs and the motor did run OK for a while, I would think that the floats are correctly set, otherwise it would have run poorly right away rather than intermittently.

Response to 2nd question: There are many possibilities as to what may be causing your intermittant problem. It could be fuel or it could be ignition related. Rather than guessing at a specific cause, I suggest first determining if the fuel supply is the problem. Connect a portable fuel tank directly to the motor and see if the problem persists. If the problem goes away, then you need to figure out what specific component in the fuel supply system is causing the problem but at least the range of possibilities is more limited. Another way to troubleshoot fuel supply is to connect a vacuum gauge to the fuel line (with a T connection) just before the fuel pump and confirm that the vacuum in the line does not exceed the spec. Then connect a pressure gauge to the fuel supply after the fuel pump (iusing a T connection) and confirm that the pressure does not fall below spec. If you confirm that the fuel supply is not the problem and you are confident that your carbs are OK and that you have link and synced properly, you might then check for proper spark. I like to use a SmarTach meter to check the secondary voltage in the spark plug wires when the motor is running and the intermittant poor running symptoms occur.​

I hope the above is helpful. Of course others in the forum may have more and better advice than this.​

 

[metalvolks]

Re: Merc 115 Carb Floats?

Thanks for the thorough response. I will do some of these checks tonight.

I did try the auxillary (portable tank) method last weekend. I switched it over and it ran like a dream! So... I thought... must be gunk in the main gas tank. I took it out last weekend, cleaned it out and started it up... didn't help at all. I then plugged in my auxillary/portable tank - it didn't make a difference.

Why would one day change the situation?

I'll let you know what I find tonight. Do you get pressure gauges at Napa or similar? What are the specs for that motor? Also, (since i'm a car guy not an outboard guy) the fuel pump is located on the block, correct? If so, what is the little box in the bottom of the engine cowl that the gas line quick connects/disconnects to?

Paul

 

[hkeiner]

Re: Merc 115 Carb Floats?

It seems that your fuel tank supply is OK if the portable tank test did not indicate a fuel supply problem. You probably don't need to do a fuel line vacuum test now. In case you want to do it anyway, below is a link to the Mercury Service Bulletin that describes the process. You can get a suitable vacuum gauge at almost any automotive parts store.

http://www.marinepartsman.com/Mercury-Marine-service-bulletins/Mercury-Mariner/2001/EN_17.PDF

If it were my motor with the symptoms you describe, I would do the following preliminary tests to help narrow down the problem between ignition and fuel. This is a big step towards solving the specific problem.

a) check link and sync settings (as per shop manual)
b) monitor pressure in fuel line between fuel pump and carbs when motor is stumbling (use pressure gauge and T connection)
c) monitor secondary voltage in spark plug wire when motor is stumbling (use SmartTach meter)

If both steps b) and c) show no abnormal results, you have eliminated a lot of possibilities and you can then direct your attention to other possible causes.

I hope the above is helpful. Of course others in the forum may have more and better advice than this.​

 

[sinbad jr]

Re: Merc 115 Carb Floats?

its your switch boxes all these mercs seem to have the same problem it dosent go over 22 to 2500 rpms right? dont mess with the carbs!!!!!!!!!!!

 

[Derric]

Re: Merc 115 Carb Floats?

Try running a clear fuel line from fuel pump to Carb notice if there are any air bubbles. There shouldnt be any bubbles when motor is running. If no bubbles than it isnt fuel related. Good Luck!