johnson 91 70 2 stroke

E

easy does it

Member
would't a 2 stroke be noisy and a hassle putting the oil in the gas. How long do 2 stroke engines last in comparison? Would a cruiser be underpowered with this engine?
 
The 3 cylinder looper motor from OMC! Those had and probably still have a lot of fans. They were built for decades. I had the 70 hp Evinrude version but basically the same engine on a 16 ft fiberform and it screamed. Performed like the 100hp evinrude I had on there prior.

Compared to modern four strokes its loud and smoky. It will load up while trolling and burn a ton of gas in comparison. Also you'll be buying expensive oil to mix in. I would recommend disconnecting the oil tank and measuring it yourself, if this model has the automatic oil mixer pump with tank. Those things did not last as long as the motors do and in a lot of cases were the death of these.

On the plus side, these are pretty bulletproof, and by 1991 they had all the bugs worked out. 70 hp should be plenty to get a 22 up on a plane if its propped right, unless you're at high elevation.

I'd still rather have a 4 stroke, but they weren't bad motors. There was many two stroke outboards of that era that were a lot worse.
 
I don't know what the poster is getting at, but if it is buying a used boat with an old 2 stroke, then that is one thing. You run it until you can't.

However, if the poster is wondering about buying a used 2 stroke, it is a waste of money because, as we've seen, the creeping bureaucracy and air and water pollution folks WILL, and I mean WILL get around soon to outlawing any of the older 2 strokes. The exception will be the Evinrude E-TEC class of two strokes that conform with the highest standards now due to computer controls on the engines and advances in combustion design.
 
Some of them should be banned, by the oil slick and smoke bombs they leave behind. There's no legislation even being discussed to ban them. Certain water bodies can, lake Tahoe for example has a ban on carbed two strokes. Outside of California though I don't think anyone's very concerned about it.

They'll just go the way of the dinosaurs as they age. People get tired of changing fouled plugs and mixing gas.
 
easy does it has expressed interest in boating at Lake Powell, and he lives in St George fairly close to both Lake Mead and Lake Powell. Lake Powell is about 3700 feet, and if one looses 3% of horsepower for each 1000 feet, this means that the 70 hp engine at sea level vs Lake power would loose about 11% or 7.7 hp. Thus the engine if new and in good condition would be putting out about 62.3 hp, The engine on that boat looks nice and clean, but has almost 1000 hours. A lot depends on how the engine has been maintained and run. If most of those hours are at lower speeds, and the engine was never abused, the boat will run slower, and you will have to lower the pitch of the prop to get the boat to plane, especially with cruising gear, on Powell.

If properly adjusted and in good condition, there will not be a lot of smoke when running, but more than the modern 4 strokes. It is well worth the money to have a good survey of the engine. Including sea trial with weight aboard, to give it a good load. Compression on all cylinders, leak down test and perhaps even bore scope the cylinders.

The initial C Dory was powered with a 70 hp Johnson---as this boat is. My 1993 had a 90 hp 2 stroke, and It was adequate. It is not going to be a speed demon. However if in excellent shape it may be adequate. Today, one thinks of a 972 hour motor to be "worn out". May not be the case. Many who run their motors at lower speeds can get several thousand hours.
 
My guess is that it would have run forever but:

It only had a rectifier to generate electricity which was barely enough juice to keep a smallish starting battery charged. You had to be careful even running an anchor light.

It used virtually the same fuel at slow speed (6 knots) as running at 10 to 15 (75% power?).

It would not idle worth a damn and stalled all the time usually at the most inconvenient times.

Mixing the gas was a pain and messy (it did not have oil injection).

The only good thing was that it could be started by hand - not easily - but it could (see rectifier above) and I had to do it a number of times.

The most bizarre thing was that I was thinking of replacing it (we had bought it new in 96) but couldn't figure what on earth I was going to do with it when someone stole it off the back of the boat!! The only thing I could think of is that someone in a 3rd world country really wanted a motor that can be repaired with a baseball bat.

John
 
My experience with Johnson and Evinrude 2 strokes is they last forever if the oil and gas mixture is correct. They do smoke a bit, but not as much as you'd think. A big plus to them is there isn't much to them and much to go wrong. But they are old, inefficient, underpowered (many were rated at the powerhead and not the prop), and loud.
 
They do smoke a bit, but not as much as you'd think. A big plus to them is there isn't much to them and much to go wrong. But they are old, inefficient, underpowered (many were rated at the powerhead and not the prop), and loud.
Click to expand...

This is why they are affectionately called "Keiths" (a reference to Keith Richards of The Rolling Stones) on the Arima Owners site. They smoke a lot, are old, loud, don't look so good, but last forever... :D

Chris
 
The smoke coming from a 2-stroke exhaust is from the 2-cycle oil. Use a quality oil and mix it into the gas at the correct ratio.

If possible, use an empty gas can, put the correct amount of oil into the can, then add the proper amount of gasoline. Fill the boat gas tank from the gas can.

Evinrude dealers sell a measuring cup to help get the ratio right.
 
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