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1982 Merc 50 hp 2 stroke starts for a few seconds then dies.

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planerie

New member
Ok... I just purchased an older boat with a 1982 Mercury 50HP 4 cyl 2 stroke. When I first got it I had no spark so I replaced the stator. Now I have spark, it cranks for for about 3 seconds then dies. I have to choke and throttle it all the way up for it to actually crank. It cranks revs (smokes a lot) and then dies. It will crank and do the same thing over and over every time I crank it this way. I did have an issue with losing prime but I fixed a few spots that leaked fuel and was sucking in a little air. Even after fixing those leaks it still does the same thing. The person I bought the boat from told me they had just cleaned the carbs but I took them off anyway and checked them. They do look to be cleaned and the diagrams and gaskets all look new. I am at a loss so was hoping if someone can point me in the right direction. I am no mechanic but I can pretty much fix anything if I can just get pointed in the right direction. Thanks in advance for any help you guys can give me.

Thanks,

Preston
 
Some may get tired of hearing this but the first thing to do is get a compression check and check for spark. You can get a loaner compression gauge free from Auto Zone etc...........Then start inspecting and replacing the fuel lines (all) and the wiring on your motor. The year class has a bad reputation for wiring that looses the insulation. Next, do the fuel pump and try to get it running. You may have a great motor that has a lot of life left. If your compression is good, it would be safe to spend some money on it. When it runs well enough to try it in a lake, get a Mercury Service manual and change the water pump and make sure there is no water in your lower end. Use only unleaded regular gasoline and a quality two cycle oil at 50 to 1. Sea foam added to the tanks is a very good thing. Post your results as you go. Never be afraid to ask for help. This forum is and was a Godsend for me.
 
I had a similar issue with my 1969 merc500 50hp where engine would run at idle but die if you gave it any throttle it ended up being the primer bulb one of the one way valves was getting stuck closed and only letting enough fuel for idle through. Before any major work start with the simple stuff...fuel line,the fuel and work your way back to more serious issues from there. Shop wanted to rebuild my whole carb but I just had and new it was fine.
 
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Fuddyduddy said:
Some may get tired of hearing this but the first thing to do is get a compression check and check for spark. You can get a loaner compression gauge free from Auto Zone etc...........Then start inspecting and replacing the fuel lines (all) and the wiring on your motor. The year class has a bad reputation for wiring that looses the insulation. Next, do the fuel pump and try to get it running. You may have a great motor that has a lot of life left. If your compression is good, it would be safe to spend some money on it. When it runs well enough to try it in a lake, get a Mercury Service manual and change the water pump and make sure there is no water in your lower end. Use only unleaded regular gasoline and a quality two cycle oil at 50 to 1. Sea foam added to the tanks is a very good thing. Post your results as you go. Never be afraid to ask for help. This forum is and was a Godsend for me.
Click to expand...

There is no doubt about the wiring. I took the harness off completely this past weekend and all 3 ground wires were pretty much bare with no more coating. I cleaned all the wires up really good, unwrapped them and rewrapped them with fresh new tape. Now the fun part is getting all the wires where they are supposed to go lol. I do have the wiring diagram which I will try my best to follow along with. The carbs look like they were just cleaned when I took them off and apart and the fuel lines all look brand new. Being new at this game what exactly will bad (low or high) compression do and would it cause the issue I am currently having?
 
Compression tells you whether or not your motor is worth spending time and money on. All cylinders should read close to the same, plus or minus, a few pounds. My 77 500 reads around 125Lbs for all 4, cold. Pertaining to your issue, no, but a bad cylinder can contribute to very poor performance and there are probably more than one thing causing your problem. Mine idled and ran pretty smoothly with one carb chocked off my deteriorating fuel line. I cleaned my carbs three times before I found that.
 
I had someone at work mention air flow. Do you think the cowl being clogged could cause it to run this way? I will be going work on it this afternoon and tomorrow but I was just wondering if there was no airflow if it would run a few seconds and die like its doing.
 
Try running on muffs or in a trash barrel with the cowl off and see what it does. It is simply not getting enough of what it needs whether it is fire, air, or fuel. I do appreciate your thought process on all that "could" be wrong. I suffered quite awhile trying to find the answers for mine and when it all became apparent with help from several sources, a few other problems rose up and bit me. Part of having an outboard motor, I believe. If I was not retired, the motor would have been history long ago.
 
You might try closing down the carb low idle jets and then reopening to 1 1/2 turns out each. Then try to see if it keeps running. Also sqeeze the bulb while running to see if that keeps it going.
 
I had a similar situation on my 84. Rebuilt the carbs and fuel pumps. Cranked her over and ran well. Then died shortly. Pumping the bulb was the only way she would run continually. Took the carbs back off and looked at the gasket between them and the block. I just threw them on without paying attention to the small vent hole alignment. Fixed that and it was fine. Not sure if it works in this case, but I thought I’d throw it out there.
 
Ok made some progress this weekend. I was able to get the wiring harness back in and hooked all up Friday. I went ahead and tested the compression and all 4 cyl's are 98 to 100 psi. I then installed the carbs and did what you said as far as closing the low idle jets to closed then opened 1 1/2 turn. I cranked it and it is now running with just a tad throttle and will run for a little longer at idle but then sputters and dies. It will run as long as I leave the throttle up just a hair and seems to run smooth. Now I think I am still losing some prime because after I let it run for around 30 seconds the bulb and fuel hose gets soft. I found someone in my area that said he will check the for fuel (air) leaks in my system and adjust the carbs for $65 so I will probably end up doing that instead of pulling my hair out.
 
I assume you have the 6 gallon tank with the hose and bulb. You might want to see if the arrows on the bulb are pointing in the correct direction(at the motor). Most of my air leaks came from poor fuel line and gaps in the gaskets from carbs to the block. Sounds like you are gaining on it.
 
I’m a new member and I like the help you guys are given. I’m a 9.9hp 4stroke owner��������
 
Too bad for you.

The bulb HAS to get soft when the motor is running. Try pumping it gently when the motor starts to die.

Jeff
 
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