83 140HP - Pontoon - Help!!

[larryskydives]

Here is what I have - 1985 Suntracker Pontoon and 1983 Johnson 140 HP V4.<br /><br />How far should the motor be in the water? It is a 20" motor.<br /><br />It had been sitting up for several years and I am using it now. When increasing the throttle medium to fast - at 3000 rpms the prop seems like it is slipping the water and rpms increase until I back off the throttle.<br /><br />If I increase the throttle slowly I can get to 4000 rpms before it starts.<br /><br />I am wondering if the motor is not far enough into the water. <br /><br />What is a good spec for the motor height?<br /><br />Thanks for your help.<br /><br />Larry

 

[Silvertip]

Re: 83 140HP - Pontoon - Help!!

I doubt its a motor depth problem with a 20-inch shaft. More than likely the hub of the prop is slipping. Use a scratch awl or a marker and place a mark on the hub and another in line with it on the blade area. Run the motor until the problem shows up. Check the two marks. If they no longer line up the prop needs to be replaced or re-bushed. The rubber cushion that separates the hub from the prop has broken its bond.

 

[DJ]

Re: 83 140HP - Pontoon - Help!!

Larry,<br /><br />You are cavitating. Not at all unusual for pontoons.<br /><br />However, in ideal conditions, the cavitation plate (plate above prop) should be level with the water at cruising speeds.<br /><br />You'll have to experiment. If you can, drop the engine down one bolt hole down and try.<br /><br />Also, many pontoons are overpropped (too much pitch). Your engine should be a ble to turn 5500 rpm at wide open throttle-NOT CAVITATING.<br /><br />I do not know the size of your toon, but most toon engines turn a prop in the 11" to 14" prop pitch range and are heavily cupped.