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Author Topic:   Older Mercury 90Hp

A Li Volsi posted 06-06-2002 08:14 AM ET (US)
Anyone know anything about older 90hp Mercs-like 1986?
John W posted 06-06-2002 08:54 AM ET (US)
My father has a 1983 Merc 115. I believe the 1986 90hp was still a 6 cylinder inline engine like my father's. If so, I can tell you these motors were very strong & likely generated more than their stated horsepower. They last a long time if well cared for, my uncle had a 1970's model 6 cyl. inline 90hp for 14 years in saltwater without ever flushing the motor, never had a problem & sold it in perfect running order. My father's 115 has been trouble free as well.
They're also as loud as an airplane & use alot of fuel. What specifically do you want to know?
Clark Roberts posted 06-06-2002 09:55 AM ET (US)
The 1986 year model was last of the in-line six 90hp Mercs. They would take lots of abuse and still run on and on. I have had several of these and found them to be mostly trouble free though loud and thirsty as mentioned above! They were rated at a max rpm of 5000 while their 115/135/140 counterparts were rated at 5500 rpm max! Year model 1987 90hp (70/75/80hp) were 3 cyl and rated at 5250rpm max... later in 1989 (I think) the rpm was raised on the 90 to 5500rpm but still remains 5250rpm on all but the 90... even the 4 cyl version (100/115/125) are rated at 5250rpm... blah, blah, blah,, don't know when to shut up do I? Happy Whalin'... Clark./ SCN
Bigshot posted 06-06-2002 02:41 PM ET (US)
Uh....I had had a 115 that was rated at 5500. The 90 was rated at 5200 and the 140 at 5700. But that was 1979. They are loud, thirsty, tempermental, and TALL. They are also a great engine if cared for. I still see 1960's models going strong but my 115 was a mess....always started, just might not run well, etc.
lhg posted 06-06-2002 03:19 PM ET (US)
As most know, I have a 1985 pair of these on my 18 Outrage, but in the 115 Hp version. I bought them new, and they are still running stong, with few needed repairs. They are about to get 1000 sea miles put on them cruising the British Columbia Inland Passage. On the 18 Outrage, they give me 3 miles to the gallon at 25-30 mph cruise. The best models are 1984 and later, when Mercury came out with it's excellent (and still used today) EDP painting/anti-corrosion process and integral power trim. The paint on mine is still in perfect condition, and never dulled, oxidized or peeled, with no corrosion in spite of considerable salt water usage.
In my opinion, these in-line sixes were the strongest outboards you could buy until the larger V-6's were introduced in 1976. To this day, I don't think the later Mercury 2-stroke in-line 4 115Hp engine is as fast.
If you can find a good one used, I would go for it. A friend had one on a Montauk and it was very fast.
Bigshot posted 06-06-2002 03:52 PM ET (US)
See......I was honest and did not bash the black anchors.....I mean great engines that they are:)
A Li Volsi posted 06-06-2002 07:42 PM ET (US)
I just can't seem to get it running right. Last year it would start easily and idle well and I could idle out the no wake zone easily. But when I gave it gas-it bogged down like no spark or gas. I've replace all the fuel lines form the tank to the three carbs, cleaned the tank, and replace the tank cap, water separator, and checked the fuel pump diaphram. It didn't help. Eventually a mechanic repalced the two electronic black boxes telling me it was due to fautly spark. Still never ran great- only about 3000rpm. Over the winter I rebuilt the three carbs and it starts-but won't idle and sounds like a couple of spark plug lines are out of order (which their not). Some one has told me now that I should look at the stator-something about spark again. Anyone have any similar experiences-I would appreciate the help before I throw good moneyafter bad.
Thanks-Tony
lhg posted 06-06-2002 08:10 PM ET (US)
Assuming compression is good, and powerhead/crank/pistons/rings are not shot, take it to a GOOD Mercury Dealer and have them go over it.
Boggin down and stalling out on acceleration usually means carbs are adjusted too lean.
Steve Leone posted 06-06-2002 10:26 PM ET (US)
replace the stator dude. also retard the timing 2 degrees and block the small crossover hoses on the carbs with 12 guage lead shot. mercury, the cadillac of outboards, thats why they are #1, steve out.
Steve Leone posted 06-06-2002 10:28 PM ET (US)
ps do a compression test FIRST like the man says. steve out
Steve Leone posted 06-06-2002 10:30 PM ET (US)
ps do a compression test FIRST like the man says. steve out
Steve Leone posted 06-06-2002 10:31 PM ET (US)
drugs don`t bother me, bother me, bother me......just kidding folks.
A Li Volsi posted 06-07-2002 02:21 PM ET (US)
Thanks for the replies.
Compression is good as well as the rest of the engine-it seems to have few hours on it and has been treated well, although I don't think any "real" mechanic has ever worked on it. I think a trip to a good mechanic is in order to straighten everybodys tinkering out. Just to add fuel to the fire-after rebuilding the carbs, the idle mixture screws have no affect on the way the engine runs. (and yes I was careful rebuilding them-have done several hundred auto carbs!)
lhg posted 06-07-2002 03:05 PM ET (US)
Trust me, the low speed idle mixture screws DEFINITELY have an effect on how the engine runs, idles, and starts!
Bigshot posted 06-07-2002 03:26 PM ET (US)
Larry, I think he means it is so screwed up that moving the needles does nothing, therefore something is majorly wrong.
A Li Volsi posted 06-21-2002 02:34 PM ET (US)
Thanks for all the responses.
Eventually it turned out to be the fuel pump diaphram. The engine still retained its original gray diaphram, which I learned was replaced with a new material ( the older material was known to decompose and plugged upper the carbs).

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Author	Topic: Older Mercury 90Hp
A Li Volsi	posted 06-06-2002 08:14 AM ET (US) Anyone know anything about older 90hp Mercs-like 1986?
John W	posted 06-06-2002 08:54 AM ET (US) My father has a 1983 Merc 115. I believe the 1986 90hp was still a 6 cylinder inline engine like my father's. If so, I can tell you these motors were very strong & likely generated more than their stated horsepower. They last a long time if well cared for, my uncle had a 1970's model 6 cyl. inline 90hp for 14 years in saltwater without ever flushing the motor, never had a problem & sold it in perfect running order. My father's 115 has been trouble free as well. They're also as loud as an airplane & use alot of fuel. What specifically do you want to know?
Clark Roberts	posted 06-06-2002 09:55 AM ET (US) The 1986 year model was last of the in-line six 90hp Mercs. They would take lots of abuse and still run on and on. I have had several of these and found them to be mostly trouble free though loud and thirsty as mentioned above! They were rated at a max rpm of 5000 while their 115/135/140 counterparts were rated at 5500 rpm max! Year model 1987 90hp (70/75/80hp) were 3 cyl and rated at 5250rpm max... later in 1989 (I think) the rpm was raised on the 90 to 5500rpm but still remains 5250rpm on all but the 90... even the 4 cyl version (100/115/125) are rated at 5250rpm... blah, blah, blah,, don't know when to shut up do I? Happy Whalin'... Clark./ SCN
Bigshot	posted 06-06-2002 02:41 PM ET (US) Uh....I had had a 115 that was rated at 5500. The 90 was rated at 5200 and the 140 at 5700. But that was 1979. They are loud, thirsty, tempermental, and TALL. They are also a great engine if cared for. I still see 1960's models going strong but my 115 was a mess....always started, just might not run well, etc.
lhg	posted 06-06-2002 03:19 PM ET (US) As most know, I have a 1985 pair of these on my 18 Outrage, but in the 115 Hp version. I bought them new, and they are still running stong, with few needed repairs. They are about to get 1000 sea miles put on them cruising the British Columbia Inland Passage. On the 18 Outrage, they give me 3 miles to the gallon at 25-30 mph cruise. The best models are 1984 and later, when Mercury came out with it's excellent (and still used today) EDP painting/anti-corrosion process and integral power trim. The paint on mine is still in perfect condition, and never dulled, oxidized or peeled, with no corrosion in spite of considerable salt water usage. In my opinion, these in-line sixes were the strongest outboards you could buy until the larger V-6's were introduced in 1976. To this day, I don't think the later Mercury 2-stroke in-line 4 115Hp engine is as fast. If you can find a good one used, I would go for it. A friend had one on a Montauk and it was very fast.
Bigshot	posted 06-06-2002 03:52 PM ET (US) See......I was honest and did not bash the black anchors.....I mean great engines that they are:)
A Li Volsi	posted 06-06-2002 07:42 PM ET (US) I just can't seem to get it running right. Last year it would start easily and idle well and I could idle out the no wake zone easily. But when I gave it gas-it bogged down like no spark or gas. I've replace all the fuel lines form the tank to the three carbs, cleaned the tank, and replace the tank cap, water separator, and checked the fuel pump diaphram. It didn't help. Eventually a mechanic repalced the two electronic black boxes telling me it was due to fautly spark. Still never ran great- only about 3000rpm. Over the winter I rebuilt the three carbs and it starts-but won't idle and sounds like a couple of spark plug lines are out of order (which their not). Some one has told me now that I should look at the stator-something about spark again. Anyone have any similar experiences-I would appreciate the help before I throw good moneyafter bad. Thanks-Tony
lhg	posted 06-06-2002 08:10 PM ET (US) Assuming compression is good, and powerhead/crank/pistons/rings are not shot, take it to a GOOD Mercury Dealer and have them go over it. Boggin down and stalling out on acceleration usually means carbs are adjusted too lean.
Steve Leone	posted 06-06-2002 10:26 PM ET (US) replace the stator dude. also retard the timing 2 degrees and block the small crossover hoses on the carbs with 12 guage lead shot. mercury, the cadillac of outboards, thats why they are #1, steve out.
Steve Leone	posted 06-06-2002 10:28 PM ET (US) ps do a compression test FIRST like the man says. steve out
Steve Leone	posted 06-06-2002 10:30 PM ET (US) ps do a compression test FIRST like the man says. steve out
Steve Leone	posted 06-06-2002 10:31 PM ET (US) drugs don`t bother me, bother me, bother me......just kidding folks.
A Li Volsi	posted 06-07-2002 02:21 PM ET (US) Thanks for the replies. Compression is good as well as the rest of the engine-it seems to have few hours on it and has been treated well, although I don't think any "real" mechanic has ever worked on it. I think a trip to a good mechanic is in order to straighten everybodys tinkering out. Just to add fuel to the fire-after rebuilding the carbs, the idle mixture screws have no affect on the way the engine runs. (and yes I was careful rebuilding them-have done several hundred auto carbs!)
lhg	posted 06-07-2002 03:05 PM ET (US) Trust me, the low speed idle mixture screws DEFINITELY have an effect on how the engine runs, idles, and starts!
Bigshot	posted 06-07-2002 03:26 PM ET (US) Larry, I think he means it is so screwed up that moving the needles does nothing, therefore something is majorly wrong.
A Li Volsi	posted 06-21-2002 02:34 PM ET (US) Thanks for all the responses. Eventually it turned out to be the fuel pump diaphram. The engine still retained its original gray diaphram, which I learned was replaced with a new material ( the older material was known to decompose and plugged upper the carbs).