Johnson 6hp - flat bottom jon boat help

[blakebrown71]

Hey guys,

 

   I'm hoping someone here can help me out.  Last summer I purchased an older 1436 Alumacraft flat bottom jon boat with trolling motor.  My grandpa happened to have a 1971 6hp Johnson Seahorse (3 blade prop) in his garage that had been stored properly, but hadn't been run in 20+ years.  My dad and I put a new water pump in it, checked everything and all seemed to be good, changed lower unit lube and put a new spark plug in it and she fired right up.  It seems to run great as far as I can tell, always starts right up for me on the first pull, but it doesn't seem to have anywhere close to the power and speed I'm seeing from the same or similar motors on youtube.

 

   I understand a flat bottom isn't going to cut through the water as easily, and 6hp isn't hardly anything, especially when it's pushing the boat along with my 200lb self, a half full 6 gallon gas tank, battery, 2 small anchors, and other misc. light gear.  But comparing my video below to the other links below, something doesn't seem to be right and I'm hoping someone can give me some ideas of what it might be.  Some of the attached videos are saying they're running between 10-15 mph with their 6 horse, and my phone tells me I'm usually going 3-4 mph and it sure feels like it too lol.

   I can just tell something's not right when the videos below get up to a fast enough speed to have a long, narrow wake and seem to be on plane.  Whereas my video, the boat/motor just seems to be really chugging through the water with a tall and short wake backed right up to the boat, and it doesn't seem to really be singing like the other videos.

 

   Any help is hugely appreciated!

 

 

My video: 

 

 

 

Compared to:

 

 

 

 

[Way2slow]

How much other stuff's in the boat?  TM battery and Tm will slow you down a lot. How heavy is your boat?

The motor is laboring to much to reach peak power.

What condition is the prop in?

Have you done a compression test?

May be a little rich on the high speed jet.

[fishnkamp]

Lets start with some simpler questions.  Can you measure how much of the outboard is extending below the boat.  What I am wondering is if this was a long or short shaft engine?  Your boat should have a short shaft motor I am sure.

 I would check compression and also make sure you have the correct spark plug or plugs in it.

Next, I might mix a can of Seafoam in your gas, in fact I hope that is new fuel and oil mixed properly.  Add a can or part of a can of Seafoam in the fuel and continue to run the engine on your favorite lake.  Warning it may smoke for a while it is normal, but afterword it may run cleaner and better.

Balancing the weight distribution may help too.

[JustinCT]

Above posts provide good information.  One other thing to consider, the first two videos you posted that aren't yours are different than your setup.  The first video is a v hull which will move along a little faster.  The second video is a job boat but it has virtually nothing else in it.  Weight does play a big part in how fast that motor will move you along.  If you've determined it's running correctly, could be weight related.

[Choporoz]

I run a 1976 Johnson 6 on a jon boat just like yours....I've never clocked it, but it seems about identical to your vid.

[RUSS9999]

I some time fish out of a 1436 jon boat with a old Jonson  9.9 on it. Me at 240lb him at 170lb, TM battery & TM lots of gear and a big cooler full of water for the fish it is 20 to 22mph. GPS.  I would think 6hp would be at least 15mph

[WIGuide]

One thing you have to remember is you are working with a very small amount of power with a 6 horse so weight is extra crucial. If you can get your boat to plane out your speed will increase drastically as it takes less power to push your boat on top of the water than it does to plow through the water. A few things you mentioned in your original post, that you have a tm and battery and from the video you posted it looks like those items plus yourself, your gas tank, and obviously the motor are all located in the back of the boat. The more weight you place towards the rear of the boat, the harder it is to get it to plane out.

Before you mess around with the motor, try moving your tm and battery up front and see if that improves things. Make sure your motor is set to the lowest trim setting possible and remove any weight you can from your rig. If it seems like it's close to getting up but just can't quite do it, try moving your mass forward as much as you can. Going as slow as it is you can somewhat crouch down and get as far forward as your arm will stretch just to try to get it up. It is entirely possible your boat does not have enough hp to plane out, which although that would stink, it could be a reality. Investing in something like a fin that bolts to the cavitation plate could help, or you could have the same result, so try shifting the weight first and see where that gets you. 

[blakebrown71]

I appreciate all the suggestions and questions so far! I'll get some measurements as soon as I can, but I believe the motor is a short shaft.  And to answer all the questions about weight, I completely understand this is a big factor, but like Russ9999 said above, he's got the same size/style boat fully loaded and he can get up to a pretty good speed with a 9.9, something just doesn't seem right with my 6hp absolutely plowing through the water at 4mph.

 

I'm definitely going to move the TM and battery up front and try it this weekend.  Hoping that makes a big difference because basically all of the weight on the boat is currently in the back.

[RUSS9999]

If you have it trimmed all the way down it will plow through the water and be slow.

The more weight you put up front the more you will have to trim the motor up.

[Lonnie Clemens]

If you don't think your 6 h.p. is performing correctly, I would recommend taking it to a qualified outboard motor mechanic.  They will be able to tell by doing a compression test and other things.  You have a nice motor and boat. 

 

Thank you for sharing, 

 

Lonnie

[blakebrown71]

I just wanna say thank you guys so much.  Took the boat out Friday night with the trolling motor and battery up front, and the gas tank between the bench seats instead of all the way in back.  Phone showed 10 mph and my new video looks a lot more like the other ones!  No more chugging along at 3mph!

 

You guys made my summer

 

BEFORE:

 

 

AFTER:

 

[WIGuide]

Awesome! Glad you got a little more speed out of it!