long time to plane

[breydav]

I have a 16 ft sea dart with a 1975 70hp Johnson,the engine runs great in a barrel,it has 130 lbs compression in all three cylinders,it take at least 2 city blocks long for the boat to plane ,and for the engine to come to full rpm,once it gets to full rpm it runs great,and pushes the boat around 25 to 30 mph,the prop is a 13 x 19 ,someone told me the prop should be a 17,,the engine runs great at idle and at full rpm ,the problem is between the two and getting to full rpm.

 

[v12mac]

Re: long time to plane

Since the pros will want to know what is your WOT (wide open) RPM?<br /><br />Mac

 

[red10]

Re: long time to plane

breydav, i have a 15 foot tri-hull that has the same motor and i'm running a 15 pitch prop turning 5800 rpm's so i think that 19 pitch is a little steep for your setup.

 

[DJ]

Re: long time to plane

That engine needs to be able to turn at least 5500 RPM at wide open throttle. Anything less and you are lugging it. Not good. That engine will not stand lugging.<br /><br />I would be willing to bet that a 15" prop is more in order.

 

[breydav]

Re: long time to plane

thanks for all your help,I installed the front cover plate on the carburetors(it was missing when I bought the boat)and then I cleaned the plugs did a compression test (130 all 3)checked to make sure each coil was firing ,then I went down and bought two used props a 13x15 and a 13x17,the 13x15 woke it up and the boat ran great,I have not tried the 17 yet ,I am going to buy a tach so I can tell what rpm I am turning,the boat ran a solid 32 mph,it is 17 foot long and 7ft wide inside center console SEA DART.thanks again

 

[breydav]

Re: long time to plane

thanks for all your help,I installed the front cover plate on the carburetors(it was missing when I bought the boat)and then I cleaned the plugs did a compression test (130 all 3)checked to make sure each coil was firing ,then I went down and bought two used props a 13x15 and a 13x17,the 13x15 woke it up and the boat ran great,I have not tried the 17 yet ,I am going to buy a tach so I can tell what rpm I am turning,the boat ran a solid 32 mph,it is 17 foot long and 7ft wide inside center console SEA DART.thanks again