Logo

1986 Mariner 75 hp 4 Cylinder dies at low speed around 1000 rpm HELP

86fisher

New member
HELP: My 86 Mariner 75 hp 4 cylinder has performed without problems for over 16 years. I have not been able to use it as much as years past. The last time I was out, it started like a champ, as usual, it ran great at a wide open throttle and any cruse speed on plane. It runs good at low rpm speeds not on plane, but it dies at around 1000 to 1300 rpm at trolling speed or "no wake"speed. It sarts back up fine but will die every couple of hundred feet. (it just quits) I had it out today with fresh gas, proper Quicksilver oil and Quicksilver fuel treatment. The same problem is happening again. I have Left out the "Oil Blend" device and just mixed oil in the gas like the old days. I though possibly the "Oil Blend" could have been the culprit. The "Oil Blend" has always worked fine also.(I have always winterized the Oil Blend and checked it to insure correct operation per Mercury's instructions) Is it possible I need a carburator rebuild or do I have some other issue? The only real shop work I have ever had done was a new water pump rebuild twice, just to keep a fresh impeller in place.
 
Re: 86 Mariner 75 hp 4 Cylinder dies at low speed around 1000 rpm HELP

I would do a compression and spark check first,it's getting on in years,says he whose engines are over thirty years old and one of them over forty,and sounds like it's done some hours,which is better than little.If the compression is good,within 10 -15psi down the line,and spark,though that sounds as if it is fine. After that a carb rebuild is on the cards and a fuel pump rebuild wouldn't go amiss after 16 years either,what with ethanol in gas.
 
Re: 86 Mariner 75 hp 4 Cylinder dies at low speed around 1000 rpm HELP

Thank you, I am grateful. What should the compression be? I understand the 10-15% down the line. What is the proper way to check spark? I can rebuild Rodchester and Edelbrook 4 barrel carbs on my old Chevy's. I am a fair mechanic with the means and knowledge to change engines, transmissions and rear ends on my trucks. I am a little intimidated by my Outboard. Can you recommend a manual. I have a "Seloc" Volume III, 1965-1986 6-in-line and V6 tune up and repair manual. It doesn't really cover my engine. What would the compression and spark checks tell me? I will try to research the fuel pump and carb repairs. I would prefer to pay my professional to fix it, but times are tough. If I can do it myself, I would save a lot of money. Thank you again for your free advice. (I just want to go trolling), thanks again.
 
Re: 86 Mariner 75 hp 4 Cylinder dies at low speed around 1000 rpm HELP

I should mention that I discovered the two yellow or white wires that run from the stator (alternator wires?) had corroded and the insulation deteriorated. I replaced them best I could to the point about 3" from where they entered the stator. I soldered new wires on and used heat shrink tubing and silicone to cover the splice. ??
 
Re: 86 Mariner 75 hp 4 Cylinder dies at low speed around 1000 rpm HELP

I use Seloc 3&4 cyl '65 -'89.I find it good. I would be looking for 120psi,a 100 or less,it's a rebuild,or at least a honing and re ring.If one of your cyls are down on compression it tells you have a sticking/broken ring or a damaged pot.Spark needs to be able to jump 7/16.Having spark but not strong enough to ignite the gas.
Not as hard as you might think and you will have no problem when you're mechanically minded.But before I would do that,put a can of power tune through her,then check compression again.If you have been doing a lot of tolling you will have a carbon build up,methinks.
Those two yellow wires are your stator/alternator wires. I have soldered new wire 1/2" from the stator,done the same as you and it still charges.
 
Re: 86 Mariner 75 hp 4 Cylinder dies at low speed around 1000 rpm HELP

Thank you, I picked up the spark tester today. I am reading up on that procedure, I am also reading about the compression test, I am looking for a good deal on the proper manual for this engine. I will proceed slowly, My engine has been real good to me over the years, I am optimistic that lack of use has been the cause of it's recent behavior. I am grateful for the free advise and amazed at you guys that are willing to do this. You must really love it to pay it forward. I will report my efforts as I go along. Till then, I can't wait to go fishin' .
 
When all the above advice makes no difference, readjust the throttle linkage to bring the carbs in LATER as the throttle is opened. And add an additional 1/8 of a turn CCW to each idle screw.


Jeff
 
Thank you, could you elaborate on this a little more? I am trying to wrap my brain around all of this. I understand the additional turn on the idle screws. My manual is for 6 cylinders and v-6's but the instructions and diagrams, photo's are all similar to my 4 cylinder. Where/How do I make this linkage adjustment, how much adjustment to"bring the carbs in LATER as the throttle is opened? GEE WHIZ, YOU GUYS ARE GREAT. You all are helping me to gain confidence that I can really do this. Thanks again.
 
The throttle linkage pulls the spark open THEN opens the carbs. It's a complex deal and had to figure out, but there are adjustments that allow the carbs to open later. DO that and you might loose your bogging condition. You want to delay the carb opening as much as possible.

Jeff
 
Well guys, I did the spark test and compression check. Wanted to report findings prior to possibly putting "Power Tune" thru the engine. The 4 wires all sparked what I would call strong at 7/16" of and inch, bright blue-white and consistent. This seems to be good. The compression check started out good, #1-121 PSI, #2-119 PSI, #3-119 PSI, then #4 PUMPED 119 PSI but would not hold pressure. Tried it a couple of times, checked the compression gauge adapter was screwed in tight, it's tough down there at #4. I am concerned now about what this possibly means. Based on what I have gathered from this wonderful process and reading manuals, I guess I could have one or more of the following, a stuck ring(s), a broken ring(s), a cracked or damaged piston & cylinder wall on #4. Please advise from here, have ordered the proper manual, should be here soon. I have priced the Carbs and Fuel Pump parts and was considering beginning the process of restoring the Carbs and Fuel Pump. Question: It seems like it would be worth a try to run the "Power Tune" thru, if it is stuck rings from carbon it may help, Right? Question: Years ago on an '71 Mercury 115HP 6 Cylinder, I had a discussion with the mechanic that rebuild the engine. He and I spoke at length that it was not uncommon for these older engines to have "Leaky Cases", is this valid and could this be why #4 on this engine is not holding pressure? Question: Is my "dying problem" at low RPM (1000 or lower) be the result of #4 not holding enough pressure to complete a stroke sequence and therefore it dies? Remember it starts and runs great in all ranges even at these lower RPM"S, it just dies at almost the lowest throttle position before Neutral. No warning no sputter or miss, it just dies, then it just starts right back up and off it goes. I Hope you have some optimistic feedback, Thank you in advance for your input! It is, what it is, whatever it is!
 
Re: 86 Mariner 75 hp 4 Cylinder dies at low speed around 1000 rpm HELP

icon1.png
Re: 1986 Mariner 75 hp 4 Cylinder dies at low speed around 1000 rpm HELP


Well guys, I did the spark test and compression check. Wanted to report findings prior to possibly putting "Power Tune" thru the engine. The 4 wires all sparked what I would call strong at 7/16" of and inch, bright blue-white and consistent. This seems to be good. The compression check started out good, #1-121 PSI, #2-119 PSI, #3-119 PSI, then #4 PUMPED 119 PSI but would not hold pressure. Tried it a couple of times, checked the compression gauge adapter was screwed in tight, it's tough down there at #4. I am concerned now about what this possibly means. Based on what I have gathered from this wonderful process and reading manuals, I guess I could have one or more of the following, a stuck ring(s), a broken ring(s), a cracked or damaged piston & cylinder wall on #4. Please advise from here, have ordered the proper manual, should be here soon. I have priced the Carbs and Fuel Pump parts and was considering beginning the process of restoring the Carbs and Fuel Pump. Question: It seems like it would be worth a try to run the "Power Tune" thru, if it is stuck rings from carbon it may help, Right? Question: Years ago on an '71 Mercury 115HP 6 Cylinder, I had a discussion with the mechanic that rebuild the engine. He and I spoke at length that it was not uncommon for these older engines to have "Leaky Cases", is this valid and could this be why #4 on this engine is not holding pressure? Question: Is my "dying problem" at low RPM (1000 or lower) be the result of #4 not holding enough pressure to complete a stroke sequence and therefore it dies? Remember it starts and runs great in all ranges even at these lower RPM"S, it just dies at almost the lowest throttle position before Neutral. No warning no sputter or miss, it just dies, then it just starts right back up and off it goes. I Hope you have some optimistic feedback, Thank you in advance for your input! It is, what it is, whatever it is!
 
No problem "down there" with #4 (and no head gaskets to leak on that motor). Good compression on all four. I still say the carbs need proper cleaning and/ or tuning.

Jeff
 
Those numbers are good enough and as Jeff says a carb rebuild and throw in a fuel pump rebuild as well,could have a pinhole in the pump diaphragm,or just for the fun of it
 
Thanks guys, will do. I will decide if I can do this myself or pay to have it done, manual should be here soon. I have identified the right carb kit and fuel pump kit. I am kinda excited about possibly doing this myself. I will let you know how it turns out. Thank you again for your early morning FREE advise. I am grateful.
 
Back
Top