84 Merc 115 Stalling on Throttle Up Under Load

Opus

Seaman Apprentice
Joined
Apr 24, 2008
Messages
31
Mronin' All...

Sunday morning and raining like a pig, so since I can't go out and tinker around the boat for a while, I thought I would post and annoy instead.

1984 Merc Inline 6 2 stroke. 3rd trip out this year. The season began like this - Took the boat to a local boat mechanic just for an engine check. Said the plugs were fine, motor started up great, he greased some points and changed the impeller Said nothing out o the telltale.

Took the boat out the following week and it ran great (Hard starting, but I learned here that all Merc 115's are a pain, so I learned the proper sequence and it starts easy now). Third trip out the wind was too rough - got the boat off the trailer and found I had no reverse. After being in the way of many others who were giving up and coming in to the ramp and with no reverse, my buddy and I decided to quit.

Took it home and put on the muffs - prop spun in reverse. Had ny buddy throttle back a bit while I held a 2x4 against the prop and sure enough, not turning under load.

Called the mechanic after learning here that when dropping the lower unit, if the shift shaft is not aligned correctly, gears could be messed up. Since he had recently changed the impeller, I thought...aaaahaaaa. Took it up to him and we backed it in to his big outside tank so he could check it under load. Sadly he did find the gear was stripped - I was with him and he showed it to me and replaced with one he had on the shelf - saved me a great deal of money.

Put the boat back in the tank and it shot roster tails when he throttled it up. I don't know the RPMs he got up to but the engine sounded great. But he did decide then that since he had the boat in the tank, he pulled the cowl and did some carb adjustments - said just to tweak the engine.

Next trip out was yesterday - could not get the boat to plane - sounds good, runs smooth but as I attempted to accelerate, it would begin to stall just before planing out. When I did go too far and stall, it would start back up with just a bump of the key.

I did have my buddy drive while I squeezed the bulb - found it squishy and a few pumps would bring it back to firm but it did not have any impact on the stalling. However, should the bulb be firm all the time????

A little back history - boat was bought at the end of last season - had a sluggish problem on the water and the replacement of the bulb seemed to solve that. Also drained the gas and replaced with new. Did not check the tank for sloudge, etc. And when I took it to the mechanic this season before going out, I used Seafoam in the tank at the mixture recommended on the can.

Anyway, being someone who grew up around a family owned garage, I instinctively feel it is starved for fuel and I am suspect of the adjustment the good boat mechanic made. I also read many posts here where it is said that most times when a motor drops out under load it is electrical.

Should I wait until tomorrow and call the mechanic to see if he wants to take fault in carb adjustments or should I start playing with the fuel filters, tank pickup and carb cleaners?

The way the old girl sounds, it sounds fuel starved.
 

Opus

Seaman Apprentice
Joined
Apr 24, 2008
Messages
31
Re: 84 Merc 115 Stalling on Throttle Up Under Load

Just to add a little further - got a break in the rain so I went out and pulled the cowl. Looks to me to be a fuel leak around the top carb. There is a fuel line running to the bottom of the carb from what looks to me to be a solenoid of some type - forgive me - I am a car guy so outboards are a tad new to me.

The most fuel (greenish oil residue) was found was around the area where this line went into the fitting at the bottom of the carb...as well as some areas around there. One spot actually had a drop of oil sitting - ready to drip off at the next bump of the boat, I suppose. The other carbs are clean...except the top of the one directly below, where some of this fuel dripped down on it.

I did not pull the fuel line as of yet - interesting that it has no hose clamp on it though. There are several fuel lines that do, however, actually have wire ties being used as hose clamps - is this OEM???? There is a larger size diameter fuel line that does not have a hose clamp but you can see the indentations of where it once did...

Anyway, that line I feel is leaking...it is round, going into the round nipple of the carb fitting...the body of the fitting is square so you can see some of the round tube...it seems saturated...never saw that before...if I squeeze the line, it seeps a little oil...the line is supple and has no visible leak.

Could this be my bogging out problem? Does the pressure on fuel lines increase as the RPMs go up???
 

rightcoastrob

Petty Officer 2nd Class
Joined
Jun 18, 2008
Messages
101
Re: 84 Merc 115 Stalling on Throttle Up Under Load

i got a pair of 115,s on my boat and i have to drown them in gas when its real cold out and they take a few mins to warm up.If your leaking gas at the carb from a line then its also sucking air creating a lean situation.I replaced all my lines and clamped them to the carb nipples.replace those 5 dollar primer bulbs.Mine would idle fine till i hit the gas and poof it would shut down.took my fuel pump aprt at the ramp dropped parts into the water cuz i just had rebuilt it and figured it was something i did.well it ended up being the primer bulb a 5 dollar part cost me bout 40 bucks.Im sure its probably something simple like that.And its the cheapest route to go if you dont have the know how to test the electrical.I wouldnt run out and start buying electronic parts.I know my motors are dependable ill troll all day with one and drop the hammer down and itll pull the same rpms as the port side motor.
 

Opus

Seaman Apprentice
Joined
Apr 24, 2008
Messages
31
Re: 84 Merc 115 Stalling on Throttle Up Under Load

Thanks RCR...It normally is something simple...Should the bulb be firm all the time - engine hot and underway??? Mine was not firm when I went to the back of the boat on the lake to see if pumping it more would make a difference in the bogging...But I also changed it out at the end of last season right after I got the boat and put it away for the winter...for pretty much the same reason. But even then, it would bog out a little and then pick up and go.
 

Opus

Seaman Apprentice
Joined
Apr 24, 2008
Messages
31
Re: 84 Merc 115 Stalling on Throttle Up Under Load

Friendly bttt
 

Chris1956

Supreme Mariner
Joined
Mar 25, 2004
Messages
28,102
Re: 84 Merc 115 Stalling on Throttle Up Under Load

Opus, Firstly, that motor should have a fuel enrichener instead of a choke plate. When you hit the choke button, raw fuel runs from the top carb to the intake of the other two.

Secondly, the idle mixture needs to be very rich to allow the motor to accelerate. The motor has no accelerator pumps.


It sounds like the mechanic leaned out the mixture too much. To richen it up, put the boat in the water and start and warm her up. Put it into forward. Start with the top carb, since it runs the leanest due to gravity, and open the mixture screw 1/8 turn ccw. Now try to accelerate. if no good, open the mid carb 1/8 turn and try to accelerate. if still no good open the bottom carb 1/8 turn and try again. Repeat with top followed by mid followed by bottom carbs. You want the mixture lean enough to idle reasonably well, but as rich as possible to accelerate well.
 

Opus

Seaman Apprentice
Joined
Apr 24, 2008
Messages
31
Re: 84 Merc 115 Stalling on Throttle Up Under Load

Chris,

You are spot on. I had called the mechanic this morning to tell him what was going on - he advised me pretty much what you did...he said they really are gas hogs...he told me to turn the mixture screw on each carb 1/2 turn CCW...I did so. I also changed a number of suspect fuel lines and put hose clamps where I could - only on metal nipples...none on plastic.

Put the muffs on in the driveway to make sure would start and to look for leaks - started better then it ever has.

Few hours later, down to the lake (minus fishing gear-strange feeling) and bingo - running better then then I have known it too before...No bog, no delay, up on plane and flying across the water in no time.

Thanks very much...I hope this thread and your advice helps others.
 
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