Help with an older Mercury Outboard

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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
 
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.
 
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.
 
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
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Coolest looking OB motors ever IMO. Sound great too. I've never owned one, but fuel consumption has got to be horrific.
 
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...
 
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¢
 
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!
 
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
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If you go to a site called Iboats.com go to mercury section you will find out all you need to know.
 
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.gif



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.

 
That is what an out board engine is supposed to look like ! The underneath of that boat looks dry
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. She is very pretty.
 
If there is the old black and surely hardened gas hoses ditch them. New ones on fleabay are $36 . Watch the ethanol gas . Avoid if you can. If not make sure to religiously use Stabil for Ethanol. Iboats has all the parts and info you are looking for. Their forums are quite helpful always. Be aware Sierra brand Merc parts are out there . Much cheaper than the OEM Stuff
That has Boeing pricing. There is a motor ID number search on merc.com or some such title, you'll find it. Be aware all merc parts sell by serial number for easier locating across model years. Most all that stuff you can easily cross over to Iboats and their exploded diagrams are very helpful. So is their return policy when it doesn't work out. Watch those gas tanks if they're steel. They usually rust inside. New plastic ones are far better than restoring old steel like I did, wouldn't do again..
 
Originally Posted By: dwendt44
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¢


All carburated 2-strokes are gas hogs at anything more than 80% throttle. And LOTS folks love to wind them out, so they burn significant gas. Throttle them back to 80% and they settle right down and cruise. But that is boatman talk. Weekend folks want to GO
laugh.gif
 
AWESOME homemade rig!!! The setup is just perfect considering power trim was unheard of back then with the white tower of power.
 
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