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06-01-2011, 15:38
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#1
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Registered User
Join Date: Dec 2010
Location: San Diego, California
Boat: Pearson Triton 28 (1960)
Posts: 180
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Thoughts on the Mercury Four-Stroke 9.9hp Outboard ?
Gudday!
(Hope this is the appropriate forum).
Have the opportunity to purchase a mercury 4 stroke 9.9 hp outboard for $1,500 with only 43 miles on it. Comes with lifting gear, jerry cans and a few other things. Does anyone have any experience with this motor they'd like to share?
Thanks in advance.
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07-01-2011, 21:12
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#2
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Registered User
Join Date: Oct 2007
Location: San Antonio, TX/Bocas del Toro, Panama
Boat: 1990 Macintosh 47, "Merlin"
Posts: 2,869
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We've had ours for about 2 years. Paid $1370 for it, brand new, from Academy. It was a floor model, but new.
This is a great engine. Seriously, starts nearly flawlessly (OK, sometimes I'm so confident that it will start that I take a leisurely tug on it and it doesn't start).
I guess the only thing I don't like is that over the years I've gotten used to shifting on the side of the engine, rather than on the shaft.
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07-01-2011, 21:26
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#3
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Registered User
Join Date: Sep 2010
Location: florida
Posts: 153
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I just purchased a 3.5hp I hope the 9.9 is better. On a 7 ft Livingston catamaran fiberglass dinghy(80lbs) it will barely plane with myself on board.add a second person and forget anything above 1/3rd throttle. but what really cooked my goose was 2 trips ashore (150) yds and the onboard tank was empty
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07-01-2011, 21:29
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#4
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Registered User
Join Date: Oct 2007
Location: San Antonio, TX/Bocas del Toro, Panama
Boat: 1990 Macintosh 47, "Merlin"
Posts: 2,869
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Quote:
Originally Posted by chadlaroche
I just purchased a 3.5hp I hope the 9.9 is better. On a 7 ft Livingston catamaran fiberglass dinghy(80lbs) it will barely plane with myself on board.add a second person and forget anything above 1/3rd throttle. but what really cooked my goose was 2 trips ashore (150) yds and the onboard tank was empty 
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Being honest - our problem with our 9.9 is that the gas in the tank gets old. I swear it doesn't use fuel...
I wouldn't expect an 80 lb dinghy to plane with a 3.5...
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07-01-2011, 21:40
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#5
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Registered User
Join Date: Sep 2010
Location: florida
Posts: 153
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Quote:
Originally Posted by bstreep
Being honest - our problem with our 9.9 is that the gas in the tank gets old. I swear it doesn't use fuel...
I wouldn't expect an 80 lb dinghy to plane with a 3.5...
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fair enough I had a walker bay 8' with a 4hp 2 stroke that would scoot. I expected the cat to move as well. Everyone says they dont use fuel...time to upgrade to a 9.9
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08-01-2011, 00:00
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#6
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Registered User
Join Date: Aug 2010
Location: NSW Australia
Boat: Traditional 30
Posts: 1,980
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Quote:
Originally Posted by chadlaroche
I just purchased a 3.5hp I hope the 9.9 is better. On a 7 ft Livingston catamaran fiberglass dinghy(80lbs) it will barely plane with myself on board.add a second person and forget anything above 1/3rd throttle. but what really cooked my goose was 2 trips ashore (150) yds and the onboard tank was empty 
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I dont think many people would expect a 3.5 to really plane. Particularly not on a catamaran style hull. maybe on a surfboard with an 8year old driver lol.
All that size motor is really designed for is to putt putt you to and from shore. I have a mariner 3.5 for my 8ft tender. We get around 30-40 mins motoring out of it depending on the loads.
Cheers
Oz
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08-01-2011, 10:05
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#7
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Registered User
Join Date: Dec 2010
Location: San Diego, California
Boat: Pearson Triton 28 (1960)
Posts: 180
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Thanks for all the feedback, I love this forum!
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08-01-2011, 10:17
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#8
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Registered User
Join Date: Apr 2008
Location: Brooklin, Maine U.S.A
Boat: Allures 44
Posts: 734
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For what it's worth, I believe that all the small Mercuries (9.9 included) are now the same engines as the Tohatsus.
Colin
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10-01-2011, 14:34
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#9
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Moderator Emeritus

Join Date: Sep 2007
Location: Eastern Tennessee
Boat: Research vessel for a university, retired now.
Posts: 10,405
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How old is the engine? Have you tested it? How do you know how many hours "miles" it has?
I would definitely put it on a small boat and test it with a load. Seeing that it runs with mouse ears attached may not be good enough.
__________________
David
Life begins where land ends.
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10-01-2011, 19:45
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#10
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Registered User
Join Date: Dec 2010
Location: San Diego, California
Boat: Pearson Triton 28 (1960)
Posts: 180
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Thanks, David, I think I'm going to pass on this outboard for now, but thanks for the feedback. On a much more exciting note, it looks like I'll be taking ownership of my new boat on the 13th!
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11-01-2011, 03:03
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#11
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Registered User
Join Date: Aug 2010
Location: NSW Australia
Boat: Traditional 30
Posts: 1,980
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Quote:
Originally Posted by cfarrar
For what it's worth, I believe that all the small Mercuries (9.9 included) are now the same engines as the Tohatsus.
Colin
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Agreed. I compared a Tohatsu and Merc 5 yesterday and aside from the stickers and fuel switch they were identical.
Cheers
Oz
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11-01-2011, 06:36
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#12
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Registered User
Join Date: Jan 2009
Location: Catskill Mountains when not cruising
Boat: 31' homebuilt Michalak-designed Cormorant "Sea Fever"
Posts: 2,115
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We had a Mercury 9.9 20" shaft for a few years, and it ran flawlessly.
Recently sold it and bought a new Nissan 9.8 (same as Mercury and Tohatsu) with a 25" shaft and an alternator. It also runs flawlessly. The 9.8 weighs about 25 lbs less than the 9.9, which I believe is really the 15HP motor with different carburetion. For our boat, that weight savings out on the transom was significant to the trim of the boat. And the deeper prop is wonderful when bashing into a head sea.
Both motors at less than half throttle will push our (5000 lb. -- relatively lightweight) 31' boat at 5 knots, and 15 statute miles per gallon. If we're in a hurry and want to do 6 or 7 knots, the mileage goes down to maybe 10 mpg.
Good machines all around -- treat them right and they'll treat you right. Sea Foam in the gas, regular oil changes, fresh water flush the cooling system whenever possible, fog the cylinders before winter layup, etc.
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11-01-2011, 07:34
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#13
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Registered User
Join Date: Dec 2010
Location: San Diego, California
Boat: Pearson Triton 28 (1960)
Posts: 180
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Awesome feedback, much thanks!
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11-01-2011, 08:43
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#14
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Registered User
Join Date: Mar 2006
Location: San Francisco, CA
Boat: Nordship 40ds
Posts: 3,865
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I have a Mercury 6hp and it has ran flawlessly. The only time it didn't start was when I lent it to a friend and he didn't run the engine dry before storing it. When I came back to the boat a month later I couldn't get it to start. I flushed new fuel thru it and then it started no problem.
__________________
Fair Winds,
Charlie
Between us there was, as I have already said somewhere, the bond of the sea. Besides holding our hearts together through long periods of separation, it had the effect of making us tolerant of each other's yarns -- and even convictions. Heart of Darkness
Joseph Conrad
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11-01-2011, 09:41
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#15
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Moderator Emeritus

Join Date: Sep 2007
Location: Eastern Tennessee
Boat: Research vessel for a university, retired now.
Posts: 10,405
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Charlie,
Gasoline formulated for use in California is notorious for fouling carburetors. California gasoline cannot be left in carburetors for long periods.
With the boats at work that have carburetors, when done with the boat we require that the user of the boat shut off the fuel supply and run the engine until it burns all of the fuel out of the carburetors. The only outboards that do not have this problem are the ones with fuel injection.
__________________
David
Life begins where land ends.
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