Question about a new motor install

[mattsanders]

I just put a 1977 70 hp on my 15 foot Kingfisher. The old motor was a 1971 50 hp. My 50 would push my boat at 27.2 MPH WOT. The 70 is only pushing it to 34mph WOT. Should it be faster? This is a light boat, and the Skeeter we took it off of was heavy and was running in the 36mph range. Setup seems perfect, same 17 prop.

 

[5150abf]

Re: Question about a new motor install

You need a tach to set up the new engine, outboards run to an RPM not a speed, you need to find out what RPM it is doing now to know what prop you need.

7 mph for 20 more horse doesn't seem to far off really, there may be more there btu you need to know where you are with your current prop.

 

[emdsapmgr]

Re: Question about a new motor install

Prop size will make a big difference in performance/speed. That should be propped to run 5500-5700 rpm top end. Make sure you don't have the engine mounted too low on the transom excess causing drag.