# 1974 Johnson 9.9 hp should it plain 14 ft Jon boat?



## Scott06z71 (Jun 10, 2013)

I just boat my first Jon boat. 1972 Ouachita 14 ft flat bottom 36 inch wide. It has a1974 Johnson 9.9 hp motor. I weight 280 lbs, I tried putting gas tank in front of me and 2 10 lb anchors at front of boat along with big tackle box. The boat just plows. It sounds like the motor is bogging down when full throttle. I replaced gas line from tank to motor and it runs a little better. I noticed the plastic gas tank has a crack about quarter inch long on the top and gas is leaking. I'm getting a new tank this week. Could that crack in tank be causing a fuel pressure problem making the motor bog? Should this motor be able to plane this boat with my weight?


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## stevesecotec02 (Jun 10, 2013)

That motor should plane that boat fine. A 9.9 on a 1436 should go about 15-18mph if has the right prop and its not too heavy. Your engine could need a good tune up. Whenever I buy a used outboard I always go ahead and and clean carb and install new waterpump, lowe unit oil ,coils, plugs, thermostat, fuel filter and fuel pump just for peace of mind. I just did this on a 93 25hp mariner and it only cost me $180. Also be sure to check prop for nicks or gouges.


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## Scott06z71 (Jun 10, 2013)

The guy that I bought it from said he replaced plugs and cleaned carb and water pump. I replaced thermostat and checked impeller on water pump it was a new one. I haven't pulled the plugs yet. Your suggestion of a tune up sounds like a good idea. This is my first motor smaller than an 18 hp so I wasn't sure if it was big enough. I just watched a couple you tube videos with this motor and mine does not get going like theirs did.


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## MBH (Jun 10, 2013)

What I learnt was....

Never believe the previous owner.


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## Charger25 (Jun 15, 2013)

[url=https://www.tinboats.net/forum/viewtopic.php?p=318255#p318255 said:


> MBH » 10 Jun 2013, 22:49[/url]"]What I learnt was....
> 
> Never believe the previous owner.




Agreed, Check the compression. my 7.5 will plane out the 14 footer, not a speed demon mind ya , but she will plane out. A while back I bought a '74 15hp for it. The guy who had it stated that it "ran great " Well it did , in a barrel. :---) Started on the third pull, And yes it was from a cold start. It was a few weeks before I could run it, but when I put it on the boat , it would NOT plane out.It was like a barge . Saw where the head gasket was leaking some so I ordered a new gasket. When I pulled the head , I reached in and could wiggle the piston around in the cylinder :shock: Never knew what the compression was but it couldn't been much. When I got my current '78 15 hp I offered the '74 as partial trade. I was up front with the guy about the condition of it and told him all about it. 
He said he could use it as a parts motor and knocked off some of the cost of the '78. He was an older Gentlemen, punched me in the arm and said " always check the compression you dummy" :LOL2: He then gave a gauge to check the compression on the 15 I was buying from him.


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## krawler (Jun 15, 2013)

The biggest failures on that motor are:
1.The points for the ignition. 
2. Cracked coils
3. Gummed or plugged carb.
4. Damaged prop

Run it in a barrel or on muffs, pull one spark plug wire at a time to make sure that it is running on both cylinders. That motor will run pretty good on one cylinder, just won't have any power.

Do a compression test. Should have more than 100 psi on both cylinders, More like 120 psi each.


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## Scott06z71 (Jun 16, 2013)

Thanks for the advice. I will have time this week to play around with it. As for compression check. I have never done this. I will get a compression gauge this week. Do I just remove spark plug then screw in hose and try and start the motor? I would appreciate any advice on this. Also I will pull a plug wire off while its running to check coil. I put a new gas hose and bulb from tank to motor and the motor will now idle good. I just got a new gas tank today, I found that the old had a slit in it. I hope to get it running good this week. I will post an updat later this week.


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## wingsnhammers (Jun 17, 2013)

I'm not a professional mechanic, but we always pull the plugs and thread the gauge into a plug hole and spin the motor several times. On the gauges we use, it holds the reading. As you spin the motor, you can see the needle spin up quickly. Normally, 3 good pulls on the starter rope was all that we needed to confirm compression. After you do that once, remove the gauge and thread it into the other plug hole. Then another 3 good pulls and see what ya got. You can probably find a few videos on youtube on how to do a compression check.


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