2005 Mercury 90-HP Two-stroke Saltwater Version

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Author Topic:   2005 Mercury 90-HP Two-stroke Saltwater Version

Henry posted 05-29-2007 01:30 AM ET (US)
Does anyone have any experience with [a 2005 Merucry 90-HP two-stroke saltwater version] motor? [Is this a good motor]? Does it have any recurring problems? What is the best propeller diameter and pitch for this motor when on a 17' Montauk? I would appreciate hearing about other people's experiences with this motor. Thanks.
Clark Roberts posted 05-29-2007 07:00 AM ET (US)
Henry, I have owned about a dozen of these three-cylinder Mercury motors and currently am running a 90-HP and a 75-HP (which are the same engine but one is detuned) and have never had a serious problem. The 90 is a very powerful engine and redline is at 5,500-RPM. On a Montauk it should swing a 20- to 22-inch prop. My current Montauk with a 75 swings a 20-inch Stilleto stainless three-blade at 5,300-RPM and over 40-MPH. The last 90 I had on a Montauk had a 22-inch High Five and was over 45-MPH at about 5,600-RPM (if my memory serves me correctly?). Mount engine so that anti-vent plate is about an inch above the keel and do some testing. Happy Whalin'/// Clark... SCN
PS> idle can a bit rough (fiddle with the carb "idle air" needle valves and you can smooth it somewhat) but at higher speeds it's smooth and quiet.
jimh posted 05-29-2007 08:02 AM ET (US)
This motor has all of the characteristics of a classic two-stroke outboard:
(the bad)
--noisy
--smokey
--idle speed rough
--fuel economy poor except at optimum cruise
--needs manual fuel enrichment at starting and needs warm up
--carburetor fuel system with evaporation problems
--burns oil at around 1:50 with gasoline
(and the good)
--lots of power to weight
--lots of low end torque
--simple design
--inexpensive
--reliable
This particular model has a reputation for having abundant horsepower.
Dick E posted 05-29-2007 08:02 AM ET (US)
I have a 1998 Merc 90 hp 2 stroke that has been an excellent engine
Clark has nailed the setup for you, I replaced a couple relays for the tilt/trim, but that is about it. Idle a little rough, but runs like a scalded dog
arsantella posted 07-28-2008 12:16 PM ET (US)
Last summer we Purchased a 2005 Mercury 90-HP Two stroke saltwater version with 17' Boston whaler, Montauk 1966. The boat is in great condition. The engine had starting problems. We got it professionally tuned up and we got thru the summer.
This summer the engine had starting problems again. Then it just stopped, and we had to be towed. The we tried to restart after we where towed and it started, just long enough to get us towed again. The engine is now totally rebuilt to a $4,200 bill. The mechanic told us that it overheated and then a gasket failed letting water and or oil in and out, they repaired it.
We put the boat in the water started the engine, and it failed again!!!! Back to the mechanic!!! Has anyone have a similar problem? Or can anyone give us advise?

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Author	Topic: 2005 Mercury 90-HP Two-stroke Saltwater Version
Henry	posted 05-29-2007 01:30 AM ET (US) Does anyone have any experience with [a 2005 Merucry 90-HP two-stroke saltwater version] motor? [Is this a good motor]? Does it have any recurring problems? What is the best propeller diameter and pitch for this motor when on a 17' Montauk? I would appreciate hearing about other people's experiences with this motor. Thanks.
Clark Roberts	posted 05-29-2007 07:00 AM ET (US) Henry, I have owned about a dozen of these three-cylinder Mercury motors and currently am running a 90-HP and a 75-HP (which are the same engine but one is detuned) and have never had a serious problem. The 90 is a very powerful engine and redline is at 5,500-RPM. On a Montauk it should swing a 20- to 22-inch prop. My current Montauk with a 75 swings a 20-inch Stilleto stainless three-blade at 5,300-RPM and over 40-MPH. The last 90 I had on a Montauk had a 22-inch High Five and was over 45-MPH at about 5,600-RPM (if my memory serves me correctly?). Mount engine so that anti-vent plate is about an inch above the keel and do some testing. Happy Whalin'/// Clark... SCN PS> idle can a bit rough (fiddle with the carb "idle air" needle valves and you can smooth it somewhat) but at higher speeds it's smooth and quiet.
jimh	posted 05-29-2007 08:02 AM ET (US) This motor has all of the characteristics of a classic two-stroke outboard: (the bad) --noisy --smokey --idle speed rough --fuel economy poor except at optimum cruise --needs manual fuel enrichment at starting and needs warm up --carburetor fuel system with evaporation problems --burns oil at around 1:50 with gasoline (and the good) --lots of power to weight --lots of low end torque --simple design --inexpensive --reliable This particular model has a reputation for having abundant horsepower.
Dick E	posted 05-29-2007 08:02 AM ET (US) I have a 1998 Merc 90 hp 2 stroke that has been an excellent engine Clark has nailed the setup for you, I replaced a couple relays for the tilt/trim, but that is about it. Idle a little rough, but runs like a scalded dog
arsantella	posted 07-28-2008 12:16 PM ET (US) Last summer we Purchased a 2005 Mercury 90-HP Two stroke saltwater version with 17' Boston whaler, Montauk 1966. The boat is in great condition. The engine had starting problems. We got it professionally tuned up and we got thru the summer. This summer the engine had starting problems again. Then it just stopped, and we had to be towed. The we tried to restart after we where towed and it started, just long enough to get us towed again. The engine is now totally rebuilt to a $4,200 bill. The mechanic told us that it overheated and then a gasket failed letting water and or oil in and out, they repaired it. We put the boat in the water started the engine, and it failed again!!!! Back to the mechanic!!! Has anyone have a similar problem? Or can anyone give us advise?