197? 9.9HP Mercury Outboard Motor

anchorclanker · Jul 25, 2012

Go online and look up the motor, you may find a manual or can deduce enough information to possibly help. I would also suggest the library, they should have a manual that covers that motor, or can get you one.

Except for Honda, and some oddball rarities from the distant past, most all outboards are 2 stroke until the 90's. Some have oil injection, but that motor likely used mixed fuel. Mix quality outboard motor oil 50:1 with fuel. I put some fuel in the can, gallon or so, add the appropriate amount of oil, shake it some, then top off the total amount of fuel I added oil for. More is better (within reason), less can be damaging. If in doubt go with more oil.

You really need a manual and some reading time.

kpgraci · Jul 25, 2012

PATBUZZARD said:
Greetings;
I recently picked up a 197? 9.9HP Mercury Outboard Motor. I'm pretty sure it's a 2 cycle as there's no place to check the oil\add oil. What do I need to operate this? What kind of oil, and how much do I add to the fuel? I have never had an outboard before, (most of my boating experience is in canoes\kayaks!!) The motor didn't come with any isntructions, please share anything that I should know that is not readily intuitive!

Thanks in advance,
Pat

Pat, I've got a 1973 Merc 7.5 2 stroke, a very similar motor to yours. First of all, these motors are are incredibly durable and reliable - good find.

I doubt if it is oil injected, so I'm pretty sure you need to mix the oil with the gas.

I use a premium 2 stoke outboard motor oil available at any auto parts store - I get Pennzoil but so long as it's a name brand and not some generic oil, and it must be formulated for outboards - do not use the 2 stroke oil you put in yard equipment! The oil itself is actually blue, kind of pretty.

I mix 50:1, that is, 50 parts gas to 1 part oil, there are charts on the Internet you use to figure the number of ounces of oil based on this ratio (50:1) and the size of your gas tank. I have a 2 gallon can so I put in 5oz of oil.

Also, use gas without ethanol added if possible - that's going to take some looking around as most gas stations sell 10% ethanol, but there are stations that advertise "pure gas" or "ethanol free". Ethanol in gas collects water which is bad for the engine.

My engine has 2 cylinders hence 2 spark plugs, before you run the motor for the first time pull out the plugs and with an emory board or small piece of sandpaper (220 git or so) brighten up the metal in the gap so you'll get a good spark. I use a dime to check the gap.

Starting my motor takes some technique, little two stokes can be ornery at times - full choke, full throttle, pull one or two times, reduce throttle, say 10-15% of max, pull with authority and see if you get it to hit. No doubt yours will have some special sequence that only trial and error will reveal.

Have fun!

Some other thoughts:

You can go as low as 100:1 on the oil mix, but on an older engine I like more oil than that. Anything over 50:1, say 30:1 and you run the risk of fouling the plugs.

Also, not knowing your level of engine knowledge I will add a few more tips:

Never run the motor out of the water - for testing off the boat put it in a barrel filled with at least enough water to cover the the prop plus some (half way up the shaft...)

When running, make sure you have stream of water coming out of the engine - motors that sit for a long time can have wasps and spiders build nests that block the cooling water passages :cussing:- if no water is flowing after 15 seconds or so shut it down and fix the problem.

Victory · Jul 25, 2012

The person that sold you the motor should provide you with the basic info.

Only use marine rated 2 stroke oil..... probably 50 to 1, That would be 2.5 ounces per gallon. To be sure look around on the motor for a label or tag that gives the gas oil ratio. OR call a mercury service shop. Keep a clear plastic measuring cup, funnel and a quart of oil in your lazerette. Don't waste money on other devices.

Finally, invest in a repair manual..... it'll be the best $20 you can spend.

RDS2012 · Jul 25, 2012

Sorry for hijacking this thread. Why can't you use weedwacker 2 cycle oil in gas for Outboards? What is the difference? I just bought 2 gallons of AV gas and mixed Still oil in it.

anchorclanker · Jul 25, 2012

Even considering all the advances in lubrication oils, metallurgy, and machining, and after almost two decades of pushing 100:1 oil mixes, most all outboard manufactures have reverted back to 50:1 on two strokes with mixed fuel. Too many engine failures. No matter what a motor may say to the contrary, run a 50:1 mix.

anchorclanker · Jul 25, 2012

RDS2012 said:
Sorry for hijacking this thread. Why can't you use weedwacker 2 cycle oil in gas for Outboards? What is the difference? I just bought 2 gallons of AV gas and mixed Still oil in it.

Weedwhackers, chainsaws, etc., are air cooled, and run at higher temperatures. Most outboards are liquid cooled, but even the small air cooled ones run at lower temperatures. Also, outboards often troll at idle, or run at lower power settings, where weedwhackers and chainsaws run at wide open throttle. The lower temps and low powered running require better, or at least different oils.

AV gas has lead in it, so expect so lead fouling on the plugs. I would run it in something else and mix up a batch with proper oil.

Winkfish · Jul 25, 2012

Mercs, especially the older ones, are great engines. KP offered up some great tips. I would, however, stay away from greater than 50:1 mix, as the cylinders require oil in the gas to lube them properly. A litle more oil won't hurt, but less oil could really screw you up. I always go by 8 oz oil to 3 gallons gas - 2.5/gallon is right there.

When I bought my fishing boat with a 1985 90 HP Merc, I called Mercury and peppered them with questions, and they were great. If you give them the model/serial# of your motor, they probably have the manual - best $$ you'll spend.

Also, I did try the Lowe's 2-stroke oil in another smaller motor I used to own. I ended up paying a mechanic a few hundred bucks to get it fixed after that. No more cheap 2-stroke oil for me!! There is a rating - I think TW3? - for outboard 2-stroke oil. Get the proper oil!!!

JohnS · Jul 26, 2012

kpgraci said:
Never run the motor out of the water - for testing off the boat put it in a barrel filled with at least enough water to cover the the prop plus some (half way up the shaft...)

When running, make sure you have stream of water coming out of the engine - motors that sit for a long time can have wasps and spiders build nests that block the cooling water passages :cussing:- if no water is flowing after 15 seconds or so shut it down and fix the problem.

Aside from the correct oil/gas ratio, this point is possibly most important. Their should be a steady stream of water squirting out of a small hose sticking maybe a half inch out of the back of the lower engine cowling. (If I remember correctly, its on the side opposite the tiller.) Check for this telltale every time you start the engine. The purpose of the stream is to indicate that you are in fact getting cooling water running through the engine. If you don't have a stream, stop the engine asap.

Sometimes the telltale hose can get clogged, and then maybe only a dribble will come out. That was the most common cause of a weak or non-existant telltale on our engines. We used to keep a piece of thin stiff wire in the boat to shove into the telltale hose to clean it out.

I've also seen the telltale hose come disconnected from the block, and the water flows into inside of cowling and slowly drips out through various holes.

And as kp said, never run the motor without having the lower half in the water. You can quickly burn up the rubber water pump impeller in about a minute, with no water to lubricate it.

bffatcat · Jul 27, 2012

outboard maintenence

A lot of advice on 2 stroke oil here but nobody mentioned gasoline. Gas sold at service stations today all have ethanol 10 or 15% mixed in Outboard motors dont like ethanol. If you live in a state where you can get ethanol free gas go for it. Otherwise avoid using gas with ethanol for more than 30 days. When the gas is 30 days old I dump whats left into my car`s gas tank.
Its a PITA but its better than a big repair bill

jviss · Jul 27, 2012

bffatcat said:
A lot of advice on 2 stroke oil here but nobody mentioned gasoline. Gas sold at service stations today all have ethanol 10 or 15% mixed in Outboard motors dont like ethanol. If you live in a state where you can get ethanol free gas go for it. Otherwise avoid using gas with ethanol for more than 30 days. When the gas is 30 days old I dump whats left into my car`s gas tank.
Its a PITA but its better than a big repair bill

Not a good idea with 2-stroke gas with oil added.

anchorclanker · Jul 27, 2012

bffatcat said:
A lot of advice on 2 stroke oil here but nobody mentioned gasoline. Gas sold at service stations today all have ethanol 10 or 15% mixed in Outboard motors dont like ethanol. If you live in a state where you can get ethanol free gas go for it. Otherwise avoid using gas with ethanol for more than 30 days. When the gas is 30 days old I dump whats left into my car`s gas tank.
Its a PITA but its better than a big repair bill

That stuff is known to plug catalytic converters, you may be headed for a big repair bill anyway. As long as you run the engine regularly, the alcohol isnt that big of a problem. I look at it and smell it. If its clear and smells like gas, I run it.

FourPoints · Jul 27, 2012

Winkfish said:
There is a rating - I think TW3? - for outboard 2-stroke oil. Get the proper oil!!!

TCW-3
TCW-3
TCW-3
TCW-3
TCW-3
TCW-3
TCW-3
TCW-3

The absolute most important thing for outboard engines is that the oil is TCW-3 rated, not much else matters.

In the 90's my dad ran a outboard repair business, funded mostly by people who did not use TCW-3 oil...