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pontoon with 70 hp johnson

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cds11

Contributing Member
recently got a pontoon without motor and put a 2000 Johnson 7 hp on it. didnt know I was supposed to install the motor with the cavitation plate even with the transom and installed I as low as it could go which is 6 inches below the transom . what kind of negative effects will this have on the operation of the boat? I plan on raising it up soon but was just wandering because it uses a lot of fuel and struggles with more than 4 people on board. thx, chris
 
cds11 said:
recently got a pontoon without motor and put a 2000 Johnson 70 hp on it. didnt know I was supposed to install the motor with the cavitation plate even with the transom and installed I as low as it could go which is 6 inches below the transom . what kind of negative effects will this have on the operation of the boat? I plan on raising it up soon but was just wandering because it uses a lot of fuel and struggles with more than 4 people on board. thx, chris
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Pontoon boats are notorious for drag and causing engines to lug. But, you should first confirm spark, compression, and fuel flow are all good just to make sure you aren't down a cylinder.

The cavitation plate should run on top of the water when you're on plane. Does it? If not, you need to raise the engine one set of holes on the transom and try again.

Once you get the engine height correct you next need to address the prop and WOT RPM. You need to prop the engine with your typical expected load. What prop is on the engine now? 13 1/4 X 17 is a really common prop for the 3-cylinder 2-stroke engines.

With the motor height correct and a normal load (people + stuff) you should be able to achieve 5,500 RPM at WOT. If you're WOT RPM with 4+ people on board is below that you'll need to go to a smaller pitch prop. Typically each 1" change in pitch produces a 200RPM difference. So, let's say you have a 17P and you're only getting 5,000RPM @ WOT. If you drop to a 15P you'll now get 5,400 RPM.

Depending on the size of your pontoon you might have to run a 15P or even a 13P prop. You won't necessarily go any faster, but the engine will be under less stress and run easier.

KJ
 
year 2000 johnson / evinrude 70hp 2 stroke needs to hit 6,000 rpm at wide open throttle, not 5,500 like the older bridgeports and 49 cu in motors.
like said above the ant-cavitation plate needs to be running on top of the water at planing speed.
if you look over the back of the boat at 20 mph speed you should see the cav plate on top of the water or even 2 inches above it
if it is below the water at that speed it will be a real dog on fuel and will just run like crap.
 
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