6 HP Johnson

[Tresguey]

This is my first outboard I have owned so I have a few questions. The motor is on a Sears 12 or 13 ft aluminum boat. By what I can tell the motor is a 1978. Took it to the lake in the early morning last weekend to make sure everything worked well enough before my wife got in. Started up easy. One or two pulls. Idles great. But when I give it full throttle it just seems I should be getting more out of it. I'm 225lbs and it doesn't seem to get me on plane. Is this all she has and should I just start looking for another motor? I had a buddy a while ago had about the same setup if I remember correctly and with both of us it it we went way faster and he is bigger than me. I know we got up on plane with close to 500lbs in it.

The gas tank it came with was to large to place in the back area where I wanted it (think it's a 6 gallon). So I drove to Bass Pro and bought a 3 gallon. Fits great but after the install I constantly have to pump the bulb to keep her running. I played with the vent tube and that didn't do a thing.

Any help will be much appreciated. I kind like the boat but fishing in a Sanger Super Jet with a blown big block is a bit difficult. Plus the guys with their real nice bass boats yell at me when I move from one spot to fish to another. And the trolling sucks...lol

 

[boobie]

Re: 6 HP Johnson

What's the boat rated for horse power wise ?? Got a model# of the motor ?? If you have to keep pumping the primer bulb you could have a bad fuel pump.

 

[Tresguey]

Re: 6 HP Johnson

The boat is a Sears 13 ft aluminum semi - V. From what I see the max HP is 15. The Johnson 6 HP I have shows it is a 6R78B. From what I read it is a 1978. But I also have read that the Johnson did not have a kill switch on them until 79. Either way I have seen a video of an older 6 HP Johnson pushing a larger fiberglass boat on plane. Just seems like I am not getting all she has to give.

 

[boobie]

Re: 6 HP Johnson

The only way you might be happy is to put a 15 HP on it. You've got less than half the rated HP for the boat.

 

[a70eliminator]

Re: 6 HP Johnson

This is my first outboard I have owned so I have a few questions. The motor is on a Sears 12 or 13 ft aluminum boat. By what I can tell the motor is a 1978. Took it to the lake in the early morning last weekend to make sure everything worked well enough before my wife got in. Started up easy. One or two pulls. Idles great. But when I give it full throttle it just seems I should be getting more out of it. I'm 225lbs and it doesn't seem to get me on plane. Is this all she has and should I just start looking for another motor? I had a buddy a while ago had about the same setup if I remember correctly and with both of us it it we went way faster and he is bigger than me. I know we got up on plane with close to 500lbs in it.

The gas tank it came with was to large to place in the back area where I wanted it (think it's a 6 gallon). So I drove to Bass Pro and bought a 3 gallon. Fits great but after the install I constantly have to pump the bulb to keep her running. I played with the vent tube and that didn't do a thing.

Any help will be much appreciated. I kind like the boat but fishing in a Sanger Super Jet with a blown big block is a bit difficult. Plus the guys with their real nice bass boats yell at me when I move from one spot to fish to another. And the trolling sucks...lol

Any help will be much appreciated. I kind like the boat but fishing in a Sanger Super Jet with a blown big block is a bit difficult. Plus the guys with their real nice bass boats yell at me when I move from one spot to fish to another. And the trolling sucks...lol
How Ironic is that, around here if your BASS boat doesn't have at least 300 horses of fuel injected Merc you ain't in the game. Make sure your 6hp is running both cyls.

 

[Tresguey]

Re: 6 HP Johnson

I will check to see if it is firing on both. I would rather not drop a different motor on it of it don't need to. I just feel that it it not all there. I did read on another website to check the lower case bear oil. Had milkshake in it and read that can bog it down a bit.. Only thing is, only a couple ounces came out.

 

[boobie]

Re: 6 HP Johnson

The rule of thumb is 80% of the boats rated HP to expect any performance. That would mean you need at least a 12 HP motor.

 

[nwcove]

Re: 6 HP Johnson

i agree, seems like you are asking to much of the motor to expect it to plane with 500lbs of weight plus the weight of the hull. find a little 150lb person and see how it performs with just him/her in it?

 

[racerone]

Re: 6 HP Johnson

If there were only a couple of ounces of oil you will need to investigate.--------Check the condition of the gears.-Check condition of bushing above the pinion gear.----Check condition of driveshaft bearing surface just above the pinion gear.

 

[JohnnyRudeClassics]

Re: 6 HP Johnson

Some data points for you.

I did a first run / season opening shake down run for my 1968 Evinrude 6 HP Fisherman
( essentially the same motor as the Johnson) I picked up last year and never got a chance
to run it.

On a slightly wider 12 or 13 rental. With force 3 - 4 winds it would make just over 9 mph (by GPS) running
down wind and struggled to make 7.5 against the wind. I had to be on the middle seat for the turbulence
to clean up on the stern and get on plane. All in all I'd say the motor made the low end of it's specified
operating range ( 4,000 to 5,000 RPM ), but seemed to be lugging it and much happier running along at
a fast displacement speed, i.e. 4 or 5 mph.

I have to admit, I was expecting a little more from the motor, like 10 or 12 mph.
I do not have a tach. So, next time out, I will bring a camera and after returning
home I can then use the frequency analyzer function of the freely available
Sound Card Scope to pick out the fundamental frequency of the motor in
operation and calculate the RPMs.



( Soundcard Scope )
( I physically looped the headphone audio output back into
the microphone input with a 1/8" stereo patch cord I had laying around )

RPMs = Hz / ( # of Cylinders that fire per revolution ) * 60
for our little 2-stoke OMC's
# of Cylinders that fire per revolution = 2
i.e.
RPMs = Hz / 2 * 60 = Hz * 30

It is not a real accurate technique,
the frequency analyzer has steps of about 0.9 Hz
which works out to about 27 RPM
i.e. a given calculated value is ~+/- 13 RPM
which is plenty accurate to know whether or
not you are lugging the motor much below 4,000 RPMs
or over speeding it much above 5000 RPMs.

Thus, the 6 HP Johnson from the video
in the screen cap above was running
at about

RPMs ~= 171.95 *30 = 5158.50 +/- ~13.65 RPM

I'd say that thing is rather screaming.

there is probably something out there for iPhones
and Android phones that can do the same frequency
analysis in the field using the phone's microphone

if /when I have the time, i'll look around and post
back to this thread with what I find, of course
anyone so inclined, please find such software
and post your findings here.

good luck!