74 merc 115 hp can't find problem to fix

[tinyjcboater]

i just got a 74 or 75 115hp merc that will not plane and boggs down nearly every time it is put in gear. it almost stalls when this happens. I have checked compression in all cylinders, and all are at 135 except for #1 which is at 120 psi. I have cleaned all fuel lines, carbs, and cleaned and replaced the fuel in the tank. i have checked all vacuum lines and they are clear and functional. i have checked the distributor for problems and i have found none. i am in process of finding a timing gun to check the timing. i have also run the boat inlake with load and i have disconnected every spark plug, sequentially, to find any symptoms in each cylinder. the boat remained the same. the boat will sometimes, meaning it has happen 4 or 5 times, after five minutes or more of slowly advancing the throttle, will plane off and run beautiful. the lower unit is clean and has no leaks or water in the fluid. the water intake is perfect and pushes 5 - 15 psi while running. i am lost. i don't know if it a carb problem (too much fuel) i really have no idea. any help would be greatly appreciated.

 

[LubeDude]

Re: 74 merc 115 hp can't find problem to fix

Could just simply be the wrong prop.

 

[phatmanmike]

Re: 74 merc 115 hp can't find problem to fix

rebuild your carbs comletely. also decarb your motor. what vacuum lines did you check, i have same motor and i dont have any stinkin vacuum lines...?

 

[Chris1956]

Re: 74 merc 115 hp can't find problem to fix

Tiny - Are the idle mixture settings on the carbs correct? Usually bogging is caused by the carbs being set too lean. I recommend you open the top carb 1/8 turn (CCW) and try to accelerate. If the motor accelerates smoothly, your done. If not open the mid carb 1/8 turn and try again. Repeat with bottom carb, if necessary.

 

[tinyjcboater]

Re: 74 merc 115 hp can't find problem to fix

the vacuum lines, or at least i thought they were, are the two lines running from the power head to the fuel pump on the underside of fuel pump. also i thought to mention that the motor runs fine without a load just sitting in the driveway. thanks for the help.

 

[Chris1956]

Re: 74 merc 115 hp can't find problem to fix

Tiny, the lines that run from the transfer cover to the fuel pump can be considered as "Vacuum" lines, although they alternate between vacuum and pressure to pump the fuel. I would not think your problem is with the fuel pump. The simple check is to have someone pump the primer bulb gently while trying to accelerate. If that fixes the issue, rebuild the fuel pump.

 

[mellowyellow]

Re: 74 merc 115 hp can't find problem to fix

if the exhaust is restricted it can cause this.<br />try decarb as suggested.

 

[tinyjcboater]

Re: 74 merc 115 hp can't find problem to fix

tried to decarb, used sea foam, is it normal to have discharge from the exhaust? it was light brown and black, almost muddy looking. thanks for all your help. - TJCb

 

[phatmanmike]

Re: 74 merc 115 hp can't find problem to fix

that muddy brown crap used to be in your motor... do it again, and again, untill its clean each time...run 100%synthetic oils and youll keep that brown mud crap down to a min.

 

[tinyjcboater]

Re: 74 merc 115 hp can't find problem to fix

my thanks to phatman, chris, and mellow. i am still in process of decarbing the motor. i am hoping that this clears it up. thanks again. - TJCb

 

[phatmanmike]

Re: 74 merc 115 hp can't find problem to fix

i have a 76 merc 1150 , exact motor as yours, i decarbed and it made a day and night diffrence, i did it twice, once with the liquid in the gas, about 1 gallon of gas and 1 can of decarb... then i did it with the spray in the plug holes and carb throats

 

[mellowyellow]

Re: 74 merc 115 hp can't find problem to fix

try soaking overnight with "deep-creep".<br />just be sure to put down a tarp or something to<br />catch all the sludge when it comes out. even if <br />this doesn't cure problem, it's good for the old<br />girl

 

[tinyjcboater]

Re: 74 merc 115 hp can't find problem to fix

to soak do i just pour the sea foam into each cylinder and put the spark plug back in? (after the motor is warmed) or do i leave it open? it doesn't say how or how long on the bottle and i don't want to mess up the motor. i have been just running the motor and pouring SF into each cylinder, one at a time and running the motor until all the white smoke is gone. let me know the difference. thanks

 

[mellowyellow]

Re: 74 merc 115 hp can't find problem to fix

use the aresol type which they call deep creep.<br />follow directions on can... basically warm her<br />up and spray a can into each carb (3) until motor<br />dies, then spray into cylinders, let sit awhile<br />and then watch out.

 

[tinyjcboater]

Re: 74 merc 115 hp can't find problem to fix

the boat ran great! i had it out on sunday and it took off fine. i think i am going to deep creep it again. all the help was great, which leads me to my next 2 questions. seeing as how you guys know it all and i don't, why would the ignition just not work? i will try to start the motor and it will be fine, then the next time i go to start the motor it will not even click. it's dead. full battery but nothing when i turn the key. is there a short? i have a quicksilver remote control. i know that it is not in gear when i try to start it and i also have to turn the motor hard left or hard right to get it to turn over. should i just get a new wire harness or is there another problem?<br />the other question i had was about a down drifting trim/tilt. i will put the motor all the way up and it will take about 4 minutes to return to the bottom. there are no apparent leaks and the oil reserve is full. any help or direction would be greatly appreciated.

 

[phatmanmike]

Re: 74 merc 115 hp can't find problem to fix

you have a short in you wire harness..... find it and fix it soon, cause they aint cheep new

 

[Chris1956]

Re: 74 merc 115 hp can't find problem to fix

Tiny, On your Power T/T dropping down. I have had two problems (in 20 years) with the T/T system. Both were the result of leakage past the teflon piston seal in the trim cylinders. There is a rebuild kit ($30), but it requires a special tool to reinstall the piston, and therefore I had to have a dealer reassemble the trim cylinder (another $30). I have also bought used trim cylinders from a dealer, who had them on a junk motor, and installed them myself. You can test for the problem by disconnecting one trim cylinder, plugging the lines and pumping the motor up. If it leaks down, try the other cylinder. If both sides leak down, it is likely the problem is in the control valve mounted at the base of the motor and pump.

 

[DDAADDYY]

Re: 74 merc 115 hp can't find problem to fix

Ya know this may sound silly and I'm sure you looked but I didn't when it happened to me in the middle of the lake when panic set in. The starter terminal was loose that was it. It would start then it wouldn't silly, simple but true and easy to overlook when you triumph another problem like it sounds as though you did.

 

[tinyjcboater]

Re: 74 merc 115 hp can't find problem to fix

i think there is a short in the harness. would i just take it apart and replace any bad wire? i have checked some of the easy things but i will double check the terminal. i think it is weird that i have to turn the steering wheel hard left or hard right to get it to turn over.

 

[erniex]

Re: 74 merc 115 hp can't find problem to fix

Just went through the same thing. Turned out the yellow wire that runs from the ign. switch to the solenoid had broken within the harness just forward of the plug that goes to the motor. It would only start when I turned it to the left making the wires contact. Cut back the casing, spliced in a new piece of wire, taped it up and was ready to go. This part of the harness takes a lot of stress flexing as the motor turns and over time can break wires.