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1986 Mercury dying at full throttle? 50hp

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OldMerc19

New member
I just bought a 1986 2 stroke long shaft outboard 50 hp and have been working on it for a while now. It has 4 spark plugs and 2 carbs. I have put a new starter motor on it, new spark plugs and replaced one carb. The motor doesn't run well and it sounds off. It starts right up but it seems like its only running at half power. It wont even put my 15 foot trihull (1966 sportscraft) on plane and when i push the throttle all the way down it dies. I have put in a new fuel line and ran a can of seafoam through it. When I put a pair of muffs on and run it out of the water, the engine throttles up and it sounds much better. I can push it to full throttle and it doesn't die.

I have tinkered with the jet screws on the carbs and checked to see if theres any air blowing out of the carbs which there isn't. Water comes out good from the cooling line and the lower unit has new oil. The solenoid is also new. This problem only seems to happen when i put the boat into the lake. It sounds much better when the prop doesn't have any resistance. All four of the plugs have good spark.

Background: This is my first boat that I got for a quarantine project. I repainted the whole boat top and bottom and put new fiberglass in the bilge and put a new floor. Im trying to get this motor working before I start college but I dont know what else to try.
 
Well ---They all sound good on the trailer.----Even in gear it is still neutral as the prop does no work in air !!----Do a compression test first.----Best to install a new impeller too.
 
mine was doing the same... its about the same as yours... 1985 i think 4 cylinder 2 walbro carbs 50 hp..

turned out the trigger coil was shot.. a couple of the wires were totally devoid of insulation and barely any wire left.. I also had to do some careful repairs soldering a new lead from the stator.. amazing that it was even running in that state and had not caught fire.. other than the soldering work the repair was not to0 difficult. much easier than i thought.. had to purchase a flywheel puller tool specific to the motor.. and a flywheel holder..

it appears that the assemblers got overzealous with some very tight zip ties to hold the wires in place causing a sharp kink.... over the years the insulation wore out, then moisture got in.. the trigger coil is relatively inexpensive.. bought a cdi brand... the stator on the other hand..

once fixed the motor fired right up...

the other problem thats reared its head on this motor is fuel delivery.. getting the fuel from the tank to the motor.. need to make sure all the connections are tight and the motor is not sucking air when it should be sucking fuel...

you will become an expert on the merc 50... and the starter has to come off to remove the carbs... and be sure to crawl into the boat and disconnect the battery before doing any work!

lastly pay close attention to the routing of the fuel lines , electrical wires etc.. its a tight fit in there

today i am trying to figure out if i can swap out the fuel connector at the engine for a more modern one...

good luck..
 
rocknroj said:
mine was doing the same... its about the same as yours... 1985 i think 4 cylinder 2 walbro carbs 50 hp..

turned out the trigger coil was shot.. a couple of the wires were totally devoid of insulation and barely any wire left.. I also had to do some careful repairs soldering a new lead from the stator.. amazing that it was even running in that state and had not caught fire.. other than the soldering work the repair was not to0 difficult. much easier than i thought.. had to purchase a flywheel puller tool specific to the motor.. and a flywheel holder..

it appears that the assemblers got overzealous with some very tight zip ties to hold the wires in place causing a sharp kink.... over the years the insulation wore out, then moisture got in.. the trigger coil is relatively inexpensive.. bought a cdi brand... the stator on the other hand..

once fixed the motor fired right up...

the other problem thats reared its head on this motor is fuel delivery.. getting the fuel from the tank to the motor.. need to make sure all the connections are tight and the motor is not sucking air when it should be sucking fuel...

you will become an expert on the merc 50... and the starter has to come off to remove the carbs... and be sure to crawl into the boat and disconnect the battery before doing any work!

lastly pay close attention to the routing of the fuel lines , electrical wires etc.. its a tight fit in there

today i am trying to figure out if i can swap out the fuel connector at the engine for a more modern one...

good luck..
Click to expand...

I second that! You will become a Merc Classic 50 Mechanic working on tgese! Lol. I am one on the journey myself!
 
Hey guys! 1985 mercury 50 here that’s having similar issues. I rebuilt the carbs last winter hoping this would solve my problem, but I’m still struggling to throttle up under load. The plug in cylinder #2 looks very dry and no fouling whatsoever compared to 1, 3 & 4. Any thoughts?

I replaced the switchbox years ago with a CDI one and it’s been running great...until last year. I thought the carbs just needed a cleaning, but they were spotless. I replaced my external fuel lines, but I’m wondering if the internal fuel lines need replacing to...probably should have done that when I had the carbs off. I have yet to test compression this season, but last year they were all around 120...I was happy to see that on this old girl.

thanks!
 
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