Tuning Johnson from 6 HP to 8 HP?

[biggame@c2i.net]

Hi'<br />I recently buyed an used 1991 6 hp Johnson ((J6RL)and are very pleased with the engine. It has only been used in freshwater and looks like new. On the boat which is an Norwegian Pioner 13'it tops aprx 10 knots but with more people in it- it slows down (doh!). My question to the expert panel is.<br />The 6 hp Johnson has the same engine data as the 8 hp engine and actually is a downtuned engine. Is it possible to release the last two HP's by alternate or slightly modify the engine's carb or in other ways modify the engine?

 

[R.Johnson]

Re: Tuning Johnson from 6 HP to 8 HP?

I can't really say what the difference is between the two engines. I don't think you would see much of a difference, if any on an engine of this size.

 

[Paul Moir]

Re: Tuning Johnson from 6 HP to 8 HP?

I can, and it's pretty well impossible. Among other things, the 8hp incorperates I think one extra reed petal per cylinder. This makes the intake side of the block a little different. Since the intake and cylinder side of the block are machined together for the crankshaft, if you were to switch out one, you would need the other. So you need a whole new block, reeds & plate, intake manifold, I think there's some carb differences as well.

 

[biggame@c2i.net]

Re: Tuning Johnson from 6 HP to 8 HP?

Damn!<br />Both to the surprisingly detailed- quick response and to the answer itselves. I was hoping it was kinda' straight forward, like removing a screw or file down a knob, but this seems to be an total makeover making the effort and price for doing this not worth while. I rather save my buck and go for the 9,9/15 Hp alternative. I'll have to wait to the piggy bank gets a little more money in it. Thanx anyway.<br />Today we where cruising the Oslo fjord at temps up to 32 celcius and had a wonderful time. At the boat ramp there was a family with an old boat and engine looking like new. The guy told me the engine was from 1968, a 40 HP Evinrude, a big bulky thing twice the size of todays engines at the same HP. It had only ran for å few hrs a looked like new. The surprise was the engines demand for 2 stroke oil. According to the manual it should be fed with 4% oil mix. A smoker!!<br /><br />Anyway- happy summer to you all and I hope I can get back to the forum later on

 

[Paul Moir]

Re: Tuning Johnson from 6 HP to 8 HP?

You're not the first one who's wondered about the 6/8hp. <br /><br />A '68 40hp ought to take the normal 50:1 blend (2%). You would be suprised by what that 40hp weighs compared to a new one. Hardly any difference. The cowls are huge though arn't they? And the midsection covers make 'em look bigger.

 

[biggame@c2i.net]

Re: Tuning Johnson from 6 HP to 8 HP?

Oil as lubrication has changed a lot over the years. I remember my dad svor to use the Exxon "Uniflow" on his car. After years of use the valves and head was clogged with thick tar-like stuff. I persued him to change his motor oil to Quaker State (mineral)and after a few months the engine looked like new (inspecting it from the oil fill hole).The QS had cleaned the engine internally and also made the engine more quiet. The consum of gas also declined by .02 by the mile. Is this the case for newer 2 stroke oil, where the idea was to use high quality oil as Castrol, Pennzoil or other high performance oils and maybe cut down from 50:1 to 100:1 maintaining the lubrication needed. Is synthetic oil better than mineral when it comes to lubrication and blue smoke?

 

[Paul Moir]

Re: Tuning Johnson from 6 HP to 8 HP?

It's not due to better oils. Johnson and Evinrude went to 50:1 way back in '64 is all.<br />Actually, it's not a good idea to vary the mix ratio by using a "better" oil. A number of the older engines that demanded heavier ratios do not use oil just for lubrication but for sealing the crankcase. Plus a number of them used "plain" babbitt type bearings rather than roller and ball bearings. Plain bearings (like in a car engine) need lots of oil to operate correctly. <br />So for both those reasons, you need lots of oil no matter how good it is.<br />OMC (Johnson & Evinrude) recommended 100:1 in the 1980s on their engines. They switched back to 50:1 when they found that the problem wasn't with lubrication, but because some engines left in a salt-water environment for a long time would build up rust inside the crankcase and cylinders because there wasn't enough oil left on parts. This caused some engines to fail.<br />So as you can see, recommended mix ratios really do not have a lot to do with lubrication, but other factors instead. I do like running the high quality oils though because I find they're not as smelly and smokey as typical cheap oils. They also seem to leave less deposits, but I've never tested that.

 

[jimmbo]

Re: Tuning Johnson from 6 HP to 8 HP?

Biggameviking, if the owners manual is the correct one for your engine and the 4%(24:1) is correct, then the motor ia pre 64.

 

[MOTION LINE]

Re: Tuning Johnson from 6 HP to 8 HP?

The older version has 2 reeds and the newer for example 1992 has 3.
The custom power reeds I made has also 2.
I changed the carb from a 15 hp. and works fine on my 6 hp.,
now much stronger than my older 7,5.
With the carb and reed change the engine is about as
strong as an stock 9.9. OMC but the job is not for the average Joe tuner.


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