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#4440116 - 06/24/17 08:04 AM Help with an older Mercury Outboard
Trigger Offline


Registered: 04/16/08
Posts: 25
Loc: Northern California
My son just acquired an older ski boat with an outboard Mercury motor on it and I have no idea on anything about the motor. I was hoping someone here could give me some advise. It is a late 70's or 80's ski boat. The engine is a Mercury 140HP. I know it is a two stroke, six cylinder. It is also marked Thunderbolt Ignition. The serial number is 3754838 if that helps anyone.

So I have no idea where to get any parts and don't even know what the oil ratio is. An internet search really did not help. Everything seems to default to a 150HP motor. If anyone can give me advise as to what model this is, where to find parts (Plugs, Impeller, ect.) and what the oil ratio is, I would really appreciate it. Oh yeah, it also has not run in about 5 years, but was told that it ran like a top when parked.

Thanks,
Travis

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#4440120 - 06/24/17 08:10 AM Re: Help with an older Mercury Outboard [Re: Trigger]
Bluestream Offline


Registered: 09/13/03
Posts: 5758
Loc: Waterloo, ON
You can buy parts at a Mercury dealer, or online at many places like:

https://www.marineengine.com/

https://www.marineengine.com/parts/mercury-outboard-parts/140

Mix ratio is 50:1


Edited by Bluestream (06/24/17 08:12 AM)
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#4440123 - 06/24/17 08:14 AM Re: Help with an older Mercury Outboard [Re: Trigger]
dblshock Offline


Registered: 04/24/07
Posts: 2655
Loc: WI.
beautiful engine, would be $25k if available today.
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#4440130 - 06/24/17 08:26 AM Re: Help with an older Mercury Outboard [Re: Trigger]
BigCahuna Offline


Registered: 09/29/09
Posts: 2143
Loc: Deep in the heart of Jersey

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#4440132 - 06/24/17 08:28 AM Re: Help with an older Mercury Outboard [Re: Trigger]
Donald Offline


Registered: 03/21/04
Posts: 20469
Loc: Upstate NY
So possible fuel issues in tank and carb. Drain lower unit gear oil, look for water, use Mercruiser premium gear oil at Walmart.

Change plugs.

Get new impeller kit from Merc dealer.

I would guess it's 50 to 1 ratio.

Thunderbolt is Merc name for it's breaker less high voltage ignition.
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#4440156 - 06/24/17 08:56 AM Re: Help with an older Mercury Outboard [Re: Trigger]
WobblyElvis Offline


Registered: 09/23/14
Posts: 1355
Loc: Toronto Canada
I have a service manual for older mercury outboards. I think it only covers the 6 cylinders up to 110 hp. The manual is seen here.https://www.amazon.com/Mercury-Outboards-Service-Manual-C-90-68647/dp/B00130F6K0

You can have it if you like for just the cost of shipping.

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#4440252 - 06/24/17 10:53 AM Re: Help with an older Mercury Outboard [Re: Trigger]
BrocLuno Offline


Registered: 09/06/15
Posts: 5526
Loc: Kalifornia Kollective
Good motor. Sometimes a bit of cooling issues with top 2 cylinders. Need to go through cooling system and make sure all is good. Prolly change thermostat ...

This is a good forum to discuss Merc issues: http://www.fiberglassics.com/forum/mercury-outpost.html

These motors are sought after by the go-fast crowd. If you want to find out how to hot-rod them, the boards at Scream & Fly will help you sort out rigging, weight distribution, prop'ing, etc. You can ask here: http://www.screamandfly.com/forumdisplay...1bdc60cf5cba404 laugh
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#4440273 - 06/24/17 11:32 AM Re: Help with an older Mercury Outboard [Re: Trigger]
JTK Offline


Registered: 08/14/03
Posts: 10590
Loc: Buffalo, NY
Coolest looking OB motors ever IMO. Sound great too. I've never owned one, but fuel consumption has got to be horrific.
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#4440276 - 06/24/17 11:40 AM Re: Help with an older Mercury Outboard [Re: Trigger]
SteveSRT8 Offline


Registered: 10/10/08
Posts: 18958
Loc: Sunny Florida
I used to own a 135 six banger on a 17 foot Cobia. GREAT engine. The 115 and the 135 were nearly the same except for carbs. Actually did very well on fuel for the day. Good ski motor with a smaller prop, too. Ran 52 mph in a measured mile on the Indian River. In these older 2 stroke engines the mixing of fuel was critical, if you do it right there is little to no smoke!

We ski'd all day on 12 gallons, fuel was like 39 cents at the marina...
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#4440307 - 06/24/17 12:36 PM Re: Help with an older Mercury Outboard [Re: Trigger]
dwendt44 Offline


Registered: 05/17/06
Posts: 3971
Loc: Central Wisconsin
Quote:
The 115 and the 135 were nearly the same except for carbs. Actually did very well on fuel for the day


The exhaust porting is significantly different between the two.
The in-line six had a rep for being gas hogs. Not sure if that was
true or not.

My 2
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#4440354 - 06/24/17 02:01 PM Re: Help with an older Mercury Outboard [Re: Trigger]
Trigger Offline


Registered: 04/16/08
Posts: 25
Loc: Northern California
Thank you for the great responses. I checked out some of the links you guys sent and they did not seem to recognize my serial number. I'll get to digging around it and try to find another number. Thanks again to all of you!

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#4440489 - 06/24/17 05:34 PM Re: Help with an older Mercury Outboard [Re: Trigger]
BrocLuno Offline


Registered: 09/06/15
Posts: 5526
Loc: Kalifornia Kollective
The Merc guys at Scream & Fly have these things figured out very well. Start a "newby" thread there about your motor and include a picture. They will all jump on it and offer all sorts of advice and sources smile
_________________________
Formerly in marine engineering. In an earlier life I owned my own petroleum tank truck, and hauled for the majors and independent's.

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#4442175 - 06/26/17 06:16 PM Re: Help with an older Mercury Outboard [Re: Trigger]
jeep58 Offline


Registered: 02/06/09
Posts: 42
Loc: ny
If you go to a site called Iboats.com go to mercury section you will find out all you need to know.

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#4443293 - 06/27/17 10:58 PM Re: Help with an older Mercury Outboard [Re: BrocLuno]
edhackett Offline


Registered: 06/09/03
Posts: 1928
Loc: Sequim, WA
Originally Posted By: BrocLuno
Good motor. Sometimes a bit of cooling issues with top 2 cylinders. Need to go through cooling system and make sure all is good. Prolly change thermostat ...

This is a good forum to discuss Merc issues: http://www.fiberglassics.com/forum/mercury-outpost.html

These motors are sought after by the go-fast crowd. If you want to find out how to hot-rod them, the boards at Scream & Fly will help you sort out rigging, weight distribution, prop'ing, etc. You can ask here: http://www.screamandfly.com/forumdisplay...1bdc60cf5cba404 laugh


Yes, wonderful motors. The cooling issue is air getting trapped in cooling jacket at the top. The fix is to install a fitting in one of the bosses in the upper cylinder and plumb that to the tell tale. That keeps the air purged.

Here's a picture of one being used in anger this morning. It's one of Doc Frankenmerc's motors on my brother in law's homebuilt speedster. What a great morning we had, except I got kicked out to take pictures. Speed was a few mph under the top speed of 60 mph to date. It's a 100 hp hiding under an older 80 hp cowling.

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#4443637 - 06/28/17 10:11 AM Re: Help with an older Mercury Outboard [Re: edhackett]
CT8 Offline


Registered: 10/09/14
Posts: 11012
Loc: Idaho
That is what an out board engine is supposed to look like ! The underneath of that boat looks dry grin . She is very pretty.
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