1977 johnson 85hp

[dave2517]

I have been reading through some of the old threads on getting a little more umph put of these engines...I know I am 6 cubes lower than the 115 and 140....so a big increase probably won't happen....however for what I have in it....I can afford to play a little....I have ordered a set of carbs from a 135.....I am looking for the intake filler blocks...I will find them and will install them...as well as a set of boysen power reeds....can someone give me a ballpark where to start on the high speed jets....I read they might overfuel a bit at WOT, I read the low speeds are fine....I have this on a 1986 bayliner capri, the boat is primarily used for fishing...I do pull a tuber and skier occasionally...I can get about 35 mph at 4600 rpm I am using a SS 17 pitch prop....

 

[Chinewalker]

Sorry, but it's not going to do what you want it to do with the big carbs. Simply to much air volume for he smaller cube motor.

4600 revs tells me you're a little over propped, That motor is happiest in the 5500 ballpark. You might find you pull better with a 15P prop.

 

[dave2517]

Just looking to get rpms up to the 5k range mane more

 

[dave2517]

User Emdsapmgr I read part of this on one of your posts...if you can elaborate please that would be great

 

[interalian]

I'm with Chinewalker - you're overpropped. Before trying to tune your motor for more power (and the possible risk of running too lean and grenading the motor), get your revs where they should be - 5500RPM with light load/WOT. You'll get a better holeshot for pulling tubes and skiiers and you may well get a higher top speed than you do now.

Don't get me wrong, I'm all for trying to get more go out of what ya got, but I think the OMC guys knew what they were doing and jetted/carbed these motors to make as much power as was possible for reliable operation by the everyman.

 

[dave2517]

while I do realize "there is no replacement for displacement" I am NOT a 2 stroke guru by any means however I have taken a 302 Ford changed the camshaft,intake and carb....never touching bottom end or heads and gaining 100 to 150 hp....now I am not looking for ridulous gains out 93cid...and I know I don't have can or intake options with a 2 stroke....but as far as "intake valves....do reeds not act as intake valves and by using the boysen reeds improve airflow....and the intake fillers from my reading increase velocity into the cylinder....hence intake manifold and cams....the 130 carbs have bigger throats to intake more air and fuel....correct me if I am wrong....I am not discounting anyone's opinion but I would rather have the opinion from one that has tinkered with one of these engine....(i don't think)( I heard)(a buddy said) don't compute

 

[F_R]

You should already know that when you embark on a project like this, you are in uncharted territory. Maybe you can make it better, maybe worse. You never know till you try.

 

[interalian]

The intake stuffers reduce crank case volume which increases crank case compression which boosts scavenging. To be analagous to 4-stroke, larger intake ports would roughly equate to more lift/duration on a cam.

Just noodling whilst eating my chicken soup...

 

[F_R]

There is always more to a subject than meets the eye. Related to scavenging is the pulse tuning that was part of the design.

 

[Chinewalker]

Forcing more fuel and air in does no good if there's no improvement to the exit portion of the equation - exhaust side. What goes in must come out. Boyeson reeds may help a bit across idle and mid-range. You will likely find more to be gained in optimizing set-up and propeller selection.