1983 Merc 115hp power problems

[redhurricane]

New poster, been lurking for a long time. I inherited a 15' 1984 Hydrostream Viper with a 1983 (per serial #) Merc 115hp inline 6. Boat was in storage for years, put there with a similar issue that I have searched this site over and over for a while, fixing problems as I came upon them. Basically, the engine will start, idle, and rev to 5500+ rpm with the muffs attached at the driveway. Runs great, if not under load. Every time I've launched the boat, as soon as we attempt to throttle on, the boat will not accelerate and not get above 1000-1200rpm. Giving it more throttle will cause the motor to stall. I can't even get on plane.

I've gone through and tested/replaced the following:

Water pump replaced and lower unit oil changed
Fuel pump diaphram replacement
Fuel filter replaced with high flow screw on unit
Carbuerators got a full cleaning and re-jet on the main for correct altitude (5000') Float levels checked and rechecked.
Prop changed for 5000' altitude (15 pitch from the 21 that was on it at sea level)
Stator and rectifier both replaced with new OEM parts (both failed- old stator trigger wires were completely corroded)
Compression checked on all 6, all within 6psi of each other- However checked this COLD, and all were averaging 90psi, would assume hot check would be higher?
Spark checked on all 6, plugs are all consistent color, but not light tan, slightly oily but not "fouled" looking in my opinion.

What have I missed? Reading here that these motors are picky to fuel quality, it's likely I still have some of the old fuel in the tank mixed with fresh 91 octane premix. Could it be just the balance of bad fuel? Again, runs VERY strong with no load, and will barely break 1000rpm under load.

I have not verified timing, boat came from my father and he had it running years ago until it acted like it is now (happened while at speed, boat lost significant power all at once) so I can't believe the timing has changed since it's never been modified on the flywheel.

Any help you folks can provide would be appreciated, before I drop it off at the stealership and drop trou for something I might have the mechanical ability to diagnose/fix myself. The local dealer/repair shop is a "full retail + 10%" kind of place.

 

[cell]

Re: 1983 Merc 115hp power problems

check out this page...if your not worried about the timing you can follow the carb adjustments.

http://forums.iboats.com/showthread.php?t=168855

 

[allenprimo913]

Re: 1983 Merc 115hp power problems

sorry i butt in, my flywheel only shows 1 mark line where it says

| max thats it, how would i know what to read if i use a timing light?

i have the same problem that when its on earmuffs, runs and starts fine and smooth but when i rev it up, it hesitates. i read the thread on how to adjust
with timing light but i dont have marks on my flywheel to follow where is 32 deg or 27 degrees?

i got a 1966 inline 6 mercury(2 coils, 2 points, 2 condenser, 3 carbs)
still havent tasted water since i rebuilt fuel pump and the rest i went like what you did.

any help is always appreciated.

 

[cell]

Re: 1983 Merc 115hp power problems

Personally I wouldn't worry about timing just yet.You said it ran good before.If a outboard sits for a few,generally you would want to go through the fuel system first.Try the carb adjustments on that page first,and see if you any further.remember you will most likely have to adjust out in the water too,not just in a tank...or on muffs.At least I did.Sure I must a looked goofy out there going back and forth between the throttle and the carbs...but now I have one hell of a hole shot,and its stable all through the rpm range

 

[allenprimo913]

Re: 1983 Merc 115hp power problems

thanks cell,

i know since it was down for so long, i knew i had move a lot of mechanical parts around it, i adjsuted the main linkage, the throttle cables 2 of them that if you touch one you have to adjust the other. the individual carb linkage i know i messed up when i rebuild the 3 carbs, the distributor cluster arms and idle mixture screws and the choke unit which doesnt work now but it should not matter because i have a manual lever for the choke.

i followed the manual for all these adjustment and like i said it will start all the time, one click of the ignition boooommmmmmm!!!!! and idles smoothly it doesnt backfire , just this hesitates when you rev it up, it does not die when i put it to forward or reverse but just no power when i put it to high rpm.

anyway, one source from this site mentioned , it could be the rectifier, is that possible? i am using the old rectanlge type which i dont think still in the market(3 terminas= 2 yellow, 1 red). Can i use the square black rectifier?

summer is getting close and my family wants to go tanning .. im too
shy to launch my boat with my 15 hP kicker.. it goes but not as much as the 110 hp.

help!!!!!!!!!!!!

 

[cell]

Re: 1983 Merc 115hp power problems

As far as I know the rectifier just helps with the charging.The trigger gets power straight from the battery.But I have a 71 inline,and don't know the differences if there are any.There are procedures on here for testing each of em if you search.But the fuel problem(if any) is as far as I can help due to the fact that Im not familiar with an 83's electronics.They could work the same as mine,but I don't want to give you bad advice if the don't.

Just hang tight someone else will chime in with more help.

 

[Chris1956]

Re: 1983 Merc 115hp power problems

Red, Those motors will stumble when you try to accelerate, if the carbs idle mixture is too lean. try richening it up in 1/8 turn increments, starting from top carb down, and trying to accelerate after each adjustment. When you find a setting that is lean enough to idle reasonably well, and rich enough to allow smooth acceleration, your are done.

BTW - if you continue to rev that motor in neutral, it will blow up.

 

[allenprimo913]

Re: 1983 Merc 115hp power problems

thnks,

so to make my problem more clear.

hesitates when rev up or no power when rev up, bogs down when acceleration at high rpm.

this is just carbs or fuel issues nothing to do with the electronic side of it?
am i right?

correct me there

 

[cell]

Re: 1983 Merc 115hp power problems

you will never know until you go through the fuel system,and adjust the carbs.or if you use a test meter and start probing the electronics.You can get good advise here but no one can tell you for sure if its fuel or electrical.Only you can determine that.Just with the carb adjustment...one thing at a time.