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8889 Merc not topping out

E

esharp7

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"88-89 merc inline 6 115hp 2

"88-89 merc inline 6 115hp 2 stroke. It starts up and idles great. Toss it into gear and its sluggish but eventually creeps up to a respectable speed but doesn't seem to "top" out. This motor is new to me so I've only taken it out twice. The first time it did as explained above but then it "kicked in" briefly and started cruising. It would go back and fourth and then it ran well for aproximately 6-7 mins straight before cutting out again. On the second trip out I couldnt get it to ever "kick in" again. I tried a separate fuel tank with brand new gas and a perfect mixture thinking maybe the gas was bad but it didnt work. Are you thinking fuel or electronic? Also, is there an inline filter on this motor other than the screen? Thoughts?"
 
"Eric, first off the motor is

"Eric, first off the motor is older than you think (someone lied to you) - Merc stopped building the Inline 6, 115 horse in 1979, so it's at least 10 years older than you were told.

Your issue is most likely fuel related - slight clog or varnish in the carbs, or a fuel pump diapram that is considering "retirement"..."
 
"Thanks Graham. Clean carbs an

"Thanks Graham. Clean carbs and replace diaphram. Any other suggestions? You know, I was at work and couldnt remember the year.. hence the 88-89yr. Oh well. I guess a manual is in order as well. Is there a way to rule out the electronic side of things without bringing to the repair shop?"
 
You can use an ohm meter to do

You can use an ohm meter to do some preliminary continuity tests.

The earlier 115's had a distributor (just like a car) with the last couple model years using a switchbox.

First have to determine which ignition you have since the tests are very different...
 
ok Graham- its a 78 M1150. It

ok Graham- its a 78 M1150. It has a distributor type ignition system. I took a look at the carbs and found the middle carb had a float gasket that was actualy squeezed all the way out. Is it possible this is my issue? Is it sucking in air and not fuel? obviously I have to replace these gaskets. Do the float gaskets normally come with the carb kit? Should I just do the whole carb while Im in there? Should I also just go ahead and replace the fuel pump diaphram as well? And any thoughts on the ignition system? I appreciate all your expertise.
 
"Yes, the carb is probably cau

"Yes, the carb is probably causing all your woes. Even if it isn't "all" the problems, you need to address it before you troubleshoot further.

A carb kit will contain all the gaskets and bits (at least the ones they still have in stock) available for a complete carb rebuild. You may find individual parts/gaskets/seals through a Merc dealer - originally all were available separately.

It sounds like somebody "botched" a carb job attempt, so a whole kit may be in order...

I never touched the distributor ignition systems (still had my Dad around to work on those and would have sent it his way when there was still a good few of them out there).

And I personally won't work on them even now. They are fragile, parts are near impossible to find in some cases, and rotors in particular can sell for many hundreds of dollars if you do find one.

There is a couple other guys lurking around the Merc board that can probably give you some decent advice on the ignition system.

Since I'm not a "real tech" and work from my home garage, I have the option of being picky with what I work on and it's just my lack of familiarity with that particular ignition that keeps me away from them."
 
"Thanks Guys. I will be doing

"Thanks Guys. I will be doing the above mentioned repairs and hope to let you all know how it turned out after a sea trial this weekend. Im really hoping this is a fuel system issue and not an electrical issue. I have the manual now and it seems the electrical tests are quite simple but Im sure the cost of replacing these parts can be extensive. (fingers crossed)

Side note. After digging thru the manual, I have found a part called a "mercury switch" but cannot seem to find what it is used for. Im guessing it has something to do with the power tilt and whether the engine will run or even start if its been tilted too high. The switch will has a float of sorts and shifts up and down based on gravity of the motor position. Can anyone verify this for me or am I way off mark and is this part nessecary for starting and operation? Mine is good but the wires in and out of it are in terrible shape and it may not be salvageable.

Ive got to tell you that the information in this forum is top notch and am impressed with all the help everyone is willing to give. Thanks!"
 
"Eric, the switch prevents the

"Eric, the switch prevents the motor from starting while in the up position.Safety precaution.It basicly grounds the spark.Nothing to do with the power tilt. Not familar with your motor but have a look,as you face out the back of the boat,ok ok over the transom,the right side on the bracket for a black round object,with two brown wires,one grounded,one attached to the brown from the distributor on the switch box."
 
ok guys- took it out yesterday

ok guys- took it out yesterday after cleaning and rebuilding the carbs and replacing the fuel pump diaphram and gaskets. Seemed to run better but it still cut in and out. Only hit about 4 thousand rpm. My manual says it should be maxing at around 5500. This motor has the thunderbolt distributor type ignition system. Im thinking now thats it a distributor issue. Maybe the rotor isnt working right? Can anyone point me in the next direction as to what this usually is? Could the stator or switch be the issue?
 
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