13 January 2011


A while back I posted about my inflatable boat addiction over the summer.
During that little jaunt,
there were some issues with the the outboard that was on the keeper,
an 80's 2-stroke 15 hp johnson.

On the way back to the launch ramp,
it started bogging down at high speeds.
It was getting late and we had no lights,
so instead of popping the top off we just putted back.

The next day I did the freshwater hose cleaning trick and the engine acted the same way-
idled fine but didn't accelerate at all.
When I took off the top, the engine ran fine,
I'd close the lid back, and the engine would bog down.

Well, obviously it was an air issue, right?
There are 2 little holes hidden in the rear that allow air into the lid,
so the plan was to make a couple more holes in the cowl.

A month+ later and the lid was still at the shop,
the engine sitting outside in the past rains with just an old raincoat to cover it.


Finally a couple nights ago I decided to have fun with a short project during the sweet spot hours.

The first plan was to strategically place the new holes to not mess up the graphics.
Here you can see the 2 original air holes in the handle area too.

scoop templates

Next is making some templates for some scoops.
I like making 2 versions.
The smaller one is the actual footprint of the scoop, a guide to match during forming.
The larger one is the actual sheet metal size needed before hammering the curves in.

hammered scoops

After about an hour I had some decent scoops made out some thick 16 gauge stainless.
This isn't a yacht so its not a big deal if they're not perfect.
It took more time to fit them to the curve of the cowl than it did to hammer them out.


I used some silicone to seal the joint,
just so water won't drip in there, mainly during storage really.

15 hp johnson 2-stroke outboard

Here you can see the little air cleaner.
It's a really tight design compared to other outboards.
The 15 hp Johnson/Evinrudes are really small and light for their horsepower rating.
The cabrea/suzuki 9.9 hp is way heavier and taller in comparison.
And the Nissan/Tohatsu 9.9 hp had a huge block compared to the Johnson
and weighed a ton.
It did sound more solid, so maybe better for long hauls.
I definitely liked to carry the Johnson back to the van after a day of buzzing around!

Ok where was I.
buttoned up

So back home, I started the engine up without the cap,
and let it warm up a little.
Went to put on the lid, and wow it still ran, 
no change and revved nice and high.
Than out of curiosity,
I taped the inside of the scoop holes.
No change, kinda, revved similar but didn't bog at all.
So took the tape off, and really just a slight difference.

great little motor

I'm thinking that in my rush to believe it was air starvation,
and just cause I like hammering out scoops,
I overlooked the fact that it's just a simple 2-stroke engine.
You know the mechanic's rule-
check if there's gas in the tank before you rebuild the carburetor...

In between the rainstorms this December,
I did clean it up a little bit,
wiggled the spark plug wires and stuff which could have been rubbing the cowl?
Ahh I don't know, at least it works.

Oh well.
Was it a waste of time?


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