1971 Johnson 125 questions

[regulars]

Hey everybody. Dont kill me on this post, be aware I have very little knowledge about outboard motors. So I recently bought a fishing boat that came with a nice Mariner 90hp. Runs great and has power trim. However I was able to pick up a nice running 1971 Johnson 125hp and controls for $100. It does not have power trim. I have searched for what power trim will work on this motor and have failed in my search. I was hoping my Mariner power trim would work but from the looks of it, they are not compatible. So can someone point me in the right direction of what I can use? I have looked at the cmc units, but if I could use a johnson unit Id like to. Also it appears that I might need a mounting plate for the transom for this motor? The Mariner and the Johnson hardware looks completely different. If I were to go with a cmc unit do those mount right to the boat and the motor right to the cmc or is there something else I need?

 

[boobie]

The CMC mounts as you said. Good units.

 

[regulars]

The CMC mounts as you said. Good units.

Yeah I like the sound of them, just never used one. I will probably end up going that route. Ok so next dumb q about this motor. I need a new prop, this one is chewed up. Its a 21 pitch. Any recomendations?

 

[F_R]

I don't think Johnson offered power TRIM in 1971. Possibly power TILT. And when they did come out with power trim (1973??), they were a hang-on unit that wasn't very good. I wouldn't waste my time trying to look for one. I could be wrong on the years'.

 

[jimmbo]

You were right about the year for power trim, it was 1973. Power tilt was first offered back in 1960 or 61.

 

[regulars]

Ok so I ended up picking up a almost new CMC 130 unit for $300, so the tilt issue is resolved. A few other questions. Anybody know what the fuel mix ratio is on these motors? My current motor is oil injected. This one obviously is not

 

[boobie]

50:1 fuel mix.

 

[Faztbullet]

I would stay with the Mariner as it the about same HP at prop as the 125, the 125 is powerhead rated,electric shift with the old pulse pack ignition

 

[regulars]

This Powerhead has been upgraded with Holley carbs and fuel pump and converted to CDI. Not sure how much of a difference all those upgrades will make.

 

[Faztbullet]

No such thing as Holley carbs for outboard....

 

[regulars]

Ill take a look and see what they are marked. I seen the holley info decal on the head for the fuel pump, it is 110gph pump, guy a i got it from said the carbs were upgraded to holleys. I seen the CDI box, not sure of brand but is there

 

[jimmbo]

Holley carbs on an outboard? The only carbs OMC used on these engines were made by OMC I wonder what other BS the seller told you? I would be leery of using an Automotive fuel pump also, will produce far more pressure than the fuel system was designed to operate under.

 

[regulars]

The fuel pump says it is Marine and 110gph. I did not see any Holley markings on the carbs. I would imagine that the guy who he got it from years ago told him that or maybe something was lost in translation. The fuel pump is tagged holley though, so maybe thats where the communication issue is. The seller is a good guy, I know him.
So with this motor why is there such a power drop from powerhead to prop that it would equal the same prop hp as my Mariner 90hp? What is the root cause?

 

[F_R]

I don't believe that power drop stuff either. More BS to get people to buy motors. And your '71 came with CDI ignition, made by Prestolite, but might not have their name on it. It was the old battery powered CDI system. Let's hope that 110 GPH is a tad overkill. Good grief. As long as the pressure is right, it should be OK.

Lessee, the math boggles my mind. That comes out to it can empty a 6 gallon tank in less that 11 minutes, if I'm doing it right. Way too early in the morning for such serious thinking.

 

[Faztbullet]

Its not BS as the 90hp Mariner is the old style 115 non power ported block build and puts out about 90-95 hp at prop.The 125 is a flat back and shorter stroke than regular V-4 and will be in the 88-95 hp at prop... .

 

[interalian]

Hard to believe you'd lose 35hp just turning 90 degrees through a pair of bevel gears. Imagine the heat generated in the gearcase if that's true. Traditionally, when you factor 'driveline losses' between flywheel and wheel HP on a car, the loss is in the 14% range, and that includes all the geartrain through the transmission, universal joints, differential, axles and all the bearings throughout.

 

[jimmbo]

Its not BS as the 90hp Mariner is the old style 115 non power ported block build and puts out about 90-95 hp at prop.The 125 is a flat back and shorter stroke than regular V-4 and will be in the 88-95 hp at prop... .

But the 115, both crank and prop rated models had an RPM range of 5000 - 5500.
The 90, both crank and prop rated models had an RPM range of 4500 - 5000
So I doubt the prop rated 90 was the crank rated 115.
The prop rated 115 was often said to be the crank rated 140. No it wasn't there, were some differences in the porting

The 125 was the first of the 99.6 cubic inch blocks. I suspect the 125 would have been putting out about 105hp at the prop.

 

[F_R]

Waiting for legitimate dyno test results.

 

[Faztbullet]

So I doubt the prop rated 90 was the crank rated 115. The prop rated 115 was often said to be the crank rated 140. No it wasn't there, were some differences in the porting

The 90 Merc is the old style115 non power port block and the prop rated is the old style power ported 140 block with ported pistons. The power ported 115 has a bit more intake and exhaust port timing as it more around 115-120 at prop. Just as the Johnson powerhead rated 140 is 115-120 at prop. Raced and blowed up a ton of I6 motors. I have had several 115 I6 that have embarrassed some 150 V-6 owners... I myself would not waste money on the 125 as no trim and good used parts are getting harder to find in needed to repair.

 

[F_R]

With total respect for your experience, especially in racing, I'm still waiting for dyno tests. We all know there is more to speed than just horsepower. Gearcase shape and design, prop design, height, and a host of other things. Besides, how much difference does 10 or 15 horsepower actually make on the average family barge? One or two MPH can make all the difference in the world in a race, but probably be undetectable in a heavy fiberglass deep V without a GPS.